Top 100 Entity Framework Core Interview Questions and Answers

Top 100 Entity Framework Core Interview Questions and Answers

In this article, I will discuss the most frequently asked Top 100 Entity Framework Core Interview Questions and Answers. If you face any questions in the interview that we are not covering here, please feel free to put that question(s) in the comment section, and we will definitely add that question(s) with answers as soon as possible.

When preparing for an interview focused on Entity Framework Core (EF Core), it’s crucial to cover a wide range of topics, from basics to advanced features. Here’s a comprehensive list of Entity Framework (EF) Core Interview Questions and Answers. For easy understanding, I have categorized the interview questions and answers into five sections. They are as follows:

  1. Basic EF Core Interview Questions and Answers
  2. Intermediate EF Core Interview Questions and Answers
  3. Advanced EF Core Interview Questions and Answers
  4. Practical and Best Practices EF Core Interview Questions and Answers
  5. Under the Hood EF Core Interview Questions and Answers

Basic EF Core Interview Questions and Answers

In this section, I will give the List of Basic Entity Framework (EF) Core Interview Questions and Answers.

What is Entity Framework Core?

Entity Framework Core (EF Core) is an open-source, lightweight, extensible, and cross-platform version of Entity Framework, which is Microsoft’s object-relational mapper (ORM) for .NET. It enables .NET developers to work with a database using .NET objects, eliminating the need for most of the data-access code that developers usually need to write.

How does EF Core work?

EF Core works by mapping the classes in your application to database tables and the instances of those classes (objects) to rows in those tables. It tracks changes to objects in your application and applies them to the database when you call the SaveChanges() method. It also automatically generates SQL queries for reading and writing data in the database.

What are the main components of EF Core?

The main components of EF Core include:

  • DbContext: A way to configure and use EF Core, acting as a bridge between your domain or entity classes and the database.
  • DbSet: Represents a collection of entities of a specific type that you can query and save.
  • Model: Represents the mapping between your .NET classes and the database schema.
  • Querying: Allows data to be retrieved from the database using LINQ.
  • Change Tracking: Keeps track of changes made to the entities so that it can update the database accordingly.
  • Migrations: Provides a way to update the database schema to match the data model of your application.

What are Migrations in EF Core, and why are they useful?

Migrations in EF Core are a way to update the database schema to match the current state of the application’s data model. They are useful because they allow developers to apply incremental updates to the database schema without losing data or manually writing SQL scripts. EF Core can automatically generate migrations and can be applied programmatically or via command-line tools.

Can you explain the Code-First approach in EF Core?

The Code-First approach in EF Core allows developers to define their database schema using C# classes. The framework then generates the database and tables based on these classes. This approach is useful for developers who prefer to work within the code rather than dealing with database design tools. It also allows for version control of the database schema through migrations.

What is the difference between Entity Framework and EF Core?

Entity Framework (EF) is the original ORM for .NET, which is designed to work with .NET Framework. EF Core is a complete rewrite of Entity Framework designed to work with .NET Core, making it cross-platform, lightweight, and more performant. EF Core also introduces new features and improvements over EF, such as shadow properties, global query filters, and better support for asynchronous operations.

What are shadow properties in EF Core?

Shadow properties are properties that are not defined in your .NET entity class but are defined in the EF Core model. They are useful for storing data that is not part of the domain model but is needed for database relationships or other EF Core functionalities. Shadow properties can be accessed and modified using the EF Core API but do not appear in the class code.

How does EF Core handle transactions?

EF Core supports transactions, allowing multiple database operations to be executed as one atomic operation. By default, EF Core automatically wraps a series of operations performed during a single call to SaveChanges() in a transaction. Developers can also manually begin, commit, or roll back transactions using the Database.BeginTransaction(), Commit(), and Rollback() methods, respectively.

What is lazy loading, and how is it implemented in EF Core?

Lazy loading is a pattern where the loading of related data is delayed until it is specifically requested. In EF Core, lazy loading can be implemented by installing Microsoft.EntityFrameworkCore.Proxies package and enabling it in the DbContext configuration. This involves creating virtual navigation properties in your entity classes, which EF Core will then override to add lazy loading capabilities.

How can you improve the performance of applications using EF Core?

To improve the performance of applications using EF Core, consider the following strategies:

  • Use eager loading, explicit loading, or lazy loading judiciously to load related data efficiently.
  • Minimize the use of tracking for entities when not needed by using .AsNoTracking().
  • Optimize query performance by selecting only the needed columns and avoiding N+1 queries.
  • Use batching for large updates or inserts to reduce database round-trips.
  • Consider using raw SQL queries or stored procedures for complex queries or operations for better performance.

How do you define relationships in EF Core?

In EF Core, relationships between entities (tables) can be defined using navigation properties and the Fluent API or data annotations in your entity classes. There are three main types of relationships: one-to-one, one-to-many, and many-to-many.

  • One-to-One: A primary key in one entity is also a foreign key in another entity. This can be configured using the HasOne and WithOne methods in the Fluent API.
  • One-to-Many: A single entity on one side is related to multiple entities on the other side. This is represented by a collection navigation property on the one side and a foreign key on the many side. The Fluent API is configured using HasMany and WithOne.
  • Many-to-Many: Entities on both sides can relate to multiple entities on the other side. EF Core handles many-to-many relationships by implicitly creating a join table (though you can explicitly define it if needed).

What is a DbContext?

A DbContext in EF Core represents a session with the database, allowing you to query and save instances of your entities. It is a combination of the Unit Of Work and Repository patterns and provides APIs to perform CRUD operations, manage transactions, and track changes to objects. The DbContext manages the database connections and is configured with connection strings and other database-related settings.

What are Entities in EF Core?

Entities in EF Core represent the data that you want to map to the database tables. They are CLR (Common Language Runtime) classes that are mapped to database tables. An entity includes properties that map to the columns of a database table. EF Core tracks changes made to these entities and applies these changes to the database based on the type of operations performed (Create, Read, Update, Delete).

How do you handle database connections in EF Core?

Database connections in EF Core are managed by the DbContext class. You typically specify the connection string and other database provider options in the OnConfiguring method of your DbContext class or in the AddDbContext method in the Startup.cs (or a similar configuration class) of your application. EF Core opens and closes connections to the database automatically when performing operations like querying or saving data. However, you can manually control the connection using the DbContext.Database.GetDbConnection() method if you need to perform custom database operations.

What is LINQ, and how does it integrate with EF Core?

LINQ (Language Integrated Query) is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages using a syntax reminiscent of SQL but integrated into the programming language. In EF Core, LINQ queries are used to interact with the database in a strongly typed manner. You can write LINQ queries against the DbSet<TEntity> properties in your DbContext, and EF Core translates these LINQ queries into the corresponding SQL queries for the database.

EF Core’s integration with LINQ allows you to write complex queries with conditions, joins, grouping, and ordering directly in C# (or another .NET language), abstracting away the specifics of the underlying database. This integration also provides the benefits of compile-time syntax checking and IntelliSense support in IDEs like Visual Studio.

How do you use Fluent API in EF Core?

The Fluent API in EF Core is used to configure the database schema in a detailed and fluent manner, allowing for configuration beyond what data annotations can achieve. It is used inside the OnModelCreating method of your DbContext class. The Fluent API provides methods to configure aspects of your model, such as

Intermediate EF Core Interview Questions and Answers

In this section, I will give the List of Intermediate Entity Framework Core (EF Core) Interview Questions and Answers.

What is the purpose of the DbContext class in EF Core?

The DbContext class in EF Core serves as a bridge between your domain or entity classes and the database. It is responsible for managing the database connections, tracking changes to objects, querying the database, and saving changes back to the database.

Explain the role of DbSet in EF Core.

DbSet represents a collection of entities of a specific type that you can query, add, update, or remove. It provides the methods necessary for these operations and is typically used as a property within your DbContext class to access the entities of a given type.

How do you configure a one-to-many relationship using Fluent API in EF Core?

A one-to-many relationship can be configured using the Fluent API using the HasMany() and WithOne() methods. For example, if you have a Blog entity that can have many Post entities, you would configure it like this:

modelBuilder.Entity<Blog>()
    .HasMany(b => b.Posts)
    .WithOne(p => p.Blog)
    .HasForeignKey(p => p.BlogId);

This configures the relationship where a Blog has many Posts, and each Post is associated with one Blog through the BlogId foreign key.

What is Lazy Loading, and how do you enable it in EF Core?

Lazy Loading is a pattern where the loading of related data is deferred until it is explicitly requested. In EF Core, lazy loading can be enabled by installing Microsoft.EntityFrameworkCore.Proxies package and enabling it with the UseLazyLoadingProxies() method in the DbContext options builder. Additionally, navigation properties must be declared as virtual to enable them to load lazily.

Describe how to handle transactions in EF Core.

In EF Core, transactions are used to execute a set of operations as a single unit of work. EF Core supports transactions implicitly through the SaveChanges() method, which wraps the operations in a transaction. For explicit transaction control, you can use the Database.BeginTransaction(), commit the transaction with Commit(), or roll it back with Rollback() methods.

Explain the concept of Shadow Properties in EF Core.

Shadow Properties are fields in the database that do not have corresponding properties in the entity class. They are useful for storing data that should not be exposed through the entity’s API, such as audit information (e.g., CreatedAt, CreatedBy). Shadow properties are configured using the Fluent API.

How do you perform a raw SQL query in EF Core?

In EF Core, you can perform a raw SQL query using the FromSqlRaw method to query data. For example:

var blogs = context.Blogs.FromSqlRaw(“SELECT * FROM Blogs”).ToList();

To execute commands that do not return entities, you can use the ExecuteSqlRaw method.

What are Entity States in EF Core? Describe them.

Entity States in EF Core represent the state of an entity with respect to its tracking by the DbContext. The possible states are:

  • Added: The entity is new and should be inserted into the database on SaveChanges().
  • Unchanged: The entity has not been modified since it was retrieved from the database.
  • Modified: The entity has been modified, and the changes should be saved in the database.
  • Deleted: The entity has been marked for deletion from the database.
  • Detached: The entity is not being tracked by the DbContext.

How can you improve query performance in EF Core?

Improving query performance in EF Core can be achieved by:

  • Using AsNoTracking() for read-only queries to reduce overhead.
  • Selecting only the necessary columns instead of retrieving entire entities.
  • Avoid N+1 queries by eagerly loading related data when necessary.
  • Using raw SQL queries for complex queries for better efficiency.
  • Enabling query caching where appropriate.

What is the difference between Add(), Attach(), and Update() methods in EF Core?

  • Add(): Marks an entity as new. EF Core will insert it into the database on SaveChanges().
  • Attach(): Attaches an entity to the context without marking it as Added or Modified. This is useful for scenarios where you want to mark specific properties as modified.
  • Update(): Marks an entity and all its properties as Modified. EF Core will update the existing record in the database on SaveChanges(), regardless of whether the entity was previously tracked.

Explain the concept of lazy loading in EF Core.

Lazy loading is a pattern used to delay the loading of related data until it is specifically requested. In EF Core, this means that when you query for an entity, its related entities (e.g., navigation properties) are not loaded from the database immediately. Instead, they are loaded the first time they are accessed in code. To enable lazy loading in EF Core, you must install a specific NuGet package (e.g., Microsoft.EntityFrameworkCore.Proxies) and enable it in your DbContext with UseLazyLoadingProxies() method. Lazy loading can improve the performance of the initial query but can lead to the N+1 query problem if not used carefully.

What is eager loading, and how is it different from lazy loading?

Eager loading is a pattern where related data is loaded together with the main entity in a single query. In EF Core, this is achieved using the Include() method to specify related entities to be loaded. Eager loading differs from lazy loading in that it proactively fetches related data upfront, avoiding the N+1 query problem but potentially fetching more data than is necessary, which can impact performance.

How do you track changes in EF Core?

EF Core tracks changes to entities retrieved from the database through its change-tracking mechanism. When you query the database for an entity, EF Core keeps a snapshot of its original values. As you modify the entity’s properties, EF Core compares the current values to the original snapshot to determine what has changed when SaveChanges() is called. This mechanism enables EF Core to generate the appropriate SQL statements to update the database based on the changes made to the entity.

Discuss the AsNoTracking() method.

The AsNoTracking() method is used to tell EF Core not to track any changes for the returned entities. When entities are queried with AsNoTracking(), EF Core returns the entities without keeping a snapshot of their original values, which means it cannot track changes or save these entities back to the database unless they are attached to a tracking context. Using AsNoTracking() can significantly improve performance for read-only operations because it reduces the overhead associated with change tracking.

How do you perform CRUD operations in EF Core?

CRUD operations in EF Core are performed using instances of your DbContext and its DbSet properties:

  • Create: Add new entities to the context using the Add(), AddRange(), or similar methods, and then save these changes to the database with SaveChanges().
  • Read: Use LINQ queries against DbSet properties to retrieve entities from the database.
  • Update: Retrieve an entity, modify its properties, and use SaveChanges() to apply the changes to the database. EF Core’s change tracking automatically detects changes.
  • Delete: Remove entities from the context using the Remove(), RemoveRange(), or similar methods, and then use SaveChanges() to reflect the changes in the database.

Explain the role of DbSet in EF Core.

DbSet<T> represents a collection of entities of a specific type that EF Core manages. It provides the main entry point for querying and interacting with entities of a given type in the database. Through DbSet, you can perform operations like adding, removing, or querying entities. Each DbSet corresponds to a table or view in the database, and the operations performed on the DbSet are translated into SQL commands that EF Core executes against the database.

What is a composite key, and how can you configure it in EF Core?

A composite key is a key that consists of two or more columns that together uniquely identify a row in a table. In EF Core, you can configure a composite key using the Fluent API by overriding the OnModelCreating method in your DbContext class. Within this method, use the HasKey() method on the EntityTypeBuilder object to specify the properties that make up the composite key.

How do you use Fluent API in EF Core?

The Fluent API in EF Core is used to configure the model in your DbContext class. It provides a detailed, code-based method to configure your EF Core models, allowing for configurations that are not possible with data annotations alone. Here’s how you can use Fluent API in EF Core:

  • Override the OnModelCreating Method: The Fluent API configurations are placed inside the OnModelCreating method in your DbContext class. This method is called by the framework when your model is being created.
  • Configure Entity Properties and Relationships: You use the modelBuilder object provided as a parameter to the OnModelCreating method to configure entities, their properties, relationships, indexes, and more.

Discuss concurrency control in EF Core.

Concurrency control in EF Core is about ensuring that two or more database operations do not conflict with each other, particularly in scenarios where multiple processes or users attempt to modify the same data simultaneously. EF Core handles concurrency by default through optimistic concurrency control. Here’s how it works and how you can implement it:

  • Optimistic Concurrency Control: This approach assumes that conflicts are rare and doesn’t lock the data; instead, it checks for conflicts before completing the transaction. If a conflict is detected, an exception is thrown, and the application must resolve the conflict.
  • Concurrency Tokens: EF Core uses concurrency tokens to implement optimistic concurrency control. A property in your entity class can be configured as a concurrency token, which EF Core will check before performing an update or delete operation. If the token value has changed since the entity was fetched, EF Core will abort the transaction because another operation has modified the data.

Advanced EF Core Interview Questions and Answers

In this section, I will give the List of Advanced Entity Framework Core (EF Core) Interview Questions and Answers.

Explain TPH, TPT, and TPC inheritance in EF Core.

  • TPH (Table Per Hierarchy): This strategy involves using a single database table to store the data for all types in an inheritance hierarchy. Discriminator columns are used to differentiate between the types. This approach is typically more performant for querying because it avoids joins but can lead to sparse tables if there are many nullable properties only relevant to certain subclasses.
  • TPT (Table Per Type): In this strategy, each class in the inheritance hierarchy is mapped to its own database table. These tables are related through foreign keys. TPT can lead to more normalized database schemas but may suffer from performance issues due to the required joins when querying across types.
  • TPC (Table Per Concrete class): Each concrete class in the hierarchy is mapped to its own table, and these tables are not related to the database. Each table contains columns for all of the class’s properties, including those inherited. This approach can eliminate the need for joins and discriminator columns but can lead to data duplication across tables.

How do you handle transactions in EF Core?

In EF Core, transactions are used to ensure data integrity by grouping multiple operations into a single atomic operation. You can manage transactions manually using the DbContext.Database.BeginTransaction() method, or you can take advantage of EF Core’s automatic transaction management by executing operations within a SaveChanges() or SaveChangesAsync() call. Additionally, the TransactionScope class can be used to create a transaction that spans across multiple contexts.

What is an intercepting SQL Query Feature?

The SQL query interception feature in EF Core allows developers to intercept and modify SQL queries before they are executed against the database. This can be useful for logging, auditing, or applying custom logic such as dynamic filtering or data modification. You can implement this feature by overriding the OnModelCreating method in your DbContext and using the DbCommandInterceptor class to define the interception logic.

How can you optimize performance in EF Core?

Performance in EF Core can be optimized through various strategies:

  • Eager Loading: Use the Include method to preload related data within the same query to avoid the N+1 query problem.
  • Projection: Use Select to load only the necessary data fields rather than entire entities.
  • Batching: Take advantage of EF Core’s ability to batch operations to reduce round trips to the database.
  • AsNoTracking: Use AsNoTracking for read-only operations to improve query performance.
  • Indexing: Ensure proper indexing in your database to speed up query execution.
  • Pooling: Use DbContextPooling to reduce the overhead of instantiating DbContext instances.

Explain how to use stored procedures with EF Core.

In EF Core, stored procedures can be executed using the DbContext.Database.ExecuteSqlRaw or ExecuteSqlRawAsync methods for scenarios that don’t return entities. For retrieving entities, you can use the FromSqlRaw or FromSqlInterpolated methods on a DbSet to map the results of a stored procedure to entity types. Parameters can be passed to stored procedures safely to avoid SQL injection attacks.

How do you handle database versioning in EF Core migrations?

EF Core Migrations allow you to version your database schema by capturing changes in your data model. Each migration consists of a set of up (apply migration) and down (revert migration) methods. You can manage migrations using the EF Core tools (e.g., Add-Migration, Update-Database, Remove-Migration) to apply, revert, or script migrations. This approach helps manage schema changes over time, facilitating database version control.

What is the purpose of the EF Core In-Memory Database Provider?

The EF Core In-Memory Database Provider is intended for testing purposes. It allows you to run unit tests against an in-memory database that mimics the behavior of a real database system without the overhead of actual database operations. This facilitates rapid development and testing cycles by enabling the testing of data access layers without requiring an actual database connection or affecting a live database.

How do you customize code-first conventions in EF Core?

Customizing code-first conventions in EF Core involves defining your own conventions that EF Core will apply during the model-building process. You can customize conventions by overriding the OnModelCreating method in your DbContext class. Here, you can use the Fluent API to configure aspects of your model, such as property types, relationships, table names, and more, according to your specific requirements. This provides a way to apply custom configuration rules and mappings that go beyond the default conventions.

What is the DbContext Pooling in EF Core, and when should it be used?

DbContext pooling is a performance optimization feature that reuses instances of DbContext classes instead of creating new ones for each request. This reduces the overhead of initialization and disposal of DbContext instances, improving application performance. It should be used in scenarios where the application handles many short-lived DbContext instances, such as web applications.

How do Global Query Filters work in EF Core? Can you provide an example?

Global Query Filters are LINQ query predicates applied globally to all queries involving a particular entity type. They are useful for implementing soft delete functionality, multi-tenancy, or filtering data based on some global criteria. For example, you can apply a global query filter only to include active records by default:

modelBuilder.Entity<MyEntity>().HasQueryFilter(e => e.IsActive);

This ensures that queries against MyEntity will automatically filter out records where IsActive is false.

Explain the difference between Entity Framework Core’s tracking and no-tracking queries.

Tracking queries in EF Core keeps track of the changes to the returned entity instances in the context. This is useful when you intend to update the entities. No-tracking queries, on the other hand, do not keep track of changes to the entities, leading to better performance. No-tracking is useful for read-only operations. You can opt into no-tracking with .AsNoTracking() or by configuring the query at the context level.

How do you handle concurrency in EF Core?

Concurrency in EF Core is handled using concurrency tokens. A property in the entity is marked as a concurrency token using the [ConcurrencyCheck] attribute or by using Fluent API. EF Core uses this token to ensure that the entity has not been modified by another process between the time it was read and the time it was updated or deleted. If a concurrency conflict occurs, EF Core throws a DbUpdateConcurrencyException, which can be handled to implement custom conflict resolution logic.

What are Owned Entities in EF Core, and how are they used?

Owned entities in EF Core are entities that are conceptually part of another entity. They are defined using the .OwnsOne() or .OwnsMany() methods in the Fluent API. Owned entities are stored in the same table as the owning entity by default, although they can be configured to use a separate table. They are useful for encapsulating complex value types within an entity.

Explain EF Core support for Value Conversions and provide an example.

Value conversions in EF Core allow values to be converted between the database representation and the entity property type when reading from or writing to the database. This is useful for handling enumeration types, encrypting data, or working with custom types. For example, you can use value conversions to store an enumeration as a string in the database:

modelBuilder.Entity<MyEntity>()
    .Property(e => e.MyEnumProperty)
    .HasConversion(
        v => v.ToString(),
        v => (MyEnum)Enum.Parse(typeof(MyEnum), v));

EF Core implements optimistic concurrency control using concurrency tokens. A special property (e.g., a row version) in the entity is used as a concurrency token. When an entity is updated or deleted, EF Core includes the concurrency token in the WHERE clause of the SQL command. If the command affects zero rows, it means the entity was modified after it was fetched, indicating a concurrency conflict.

Can you perform raw SQL queries with EF Core? Provide an example.

Yes, EF Core allows performing raw SQL queries using the FromSqlRaw or ExecuteSqlRaw methods for querying and command execution, respectively. This is useful for executing queries or commands that cannot be expressed with LINQ. For example, to perform a raw SQL query:

var blogs = context.Blogs.FromSqlRaw(“SELECT * FROM Blogs WHERE Name = {0}”, blogName).ToList();

What are Interceptors in EF Core, and how can they be used?

Interceptors in EF Core allow you to intercept and modify operations such as command execution, transactions, and connection opening. They can be used for logging, auditing, changing command text, or implementing retry logic. You can implement an interceptor by deriving from one of the interceptor interfaces (e.g., IDbCommandInterceptor) and registering it with the DbContext.

Practical and Best Practices EF Core Interview Questions and Answers

In this section, I will give the List of Practical and Best Practices Entity Framework Core (EF Core) Interview Questions and Answers.

How do you handle model changes in EF Core without losing data?

To handle model changes without losing data, you use EF Core migrations. Migrations track changes to the model and generate code to update the database schema incrementally. To apply migrations without losing data, you carefully plan model changes, generate migrations using the Add-Migration command, review the migration code for accuracy, and apply the migration to the database using the Update-Database command, ensuring data is preserved or appropriately transformed.

What is the best way to manage database connections in EF Core?

The best way to manage database connections in EF Core is to let the context handle connections automatically. EF Core opens and closes connections as needed for operations like querying or saving data. For more control, you can manually open and close connections using the DbContext.Database property. However, always ensure connections are properly closed after use, preferably with a using statement or try-finally blocks to avoid connection leaks.

When should you use eager loading, and when should you use explicit loading in EF Core?

  • Eager Loading: Use eager loading when you know you will need related data for every entity being queried. It is done using the Include method, which loads related data as part of the initial query. This approach minimizes the number of queries but can result in large data retrieval if not used carefully.
  • Explicit Loading: Use explicit loading when you need related data conditionally or for specific entities after loading them. This is done using the Load method on the navigation property. It allows finer control over when and how much-related data is loaded.

How can you ensure thread safety when using EF Core?

To ensure thread safety with EF Core, avoid sharing DbContext instances across threads. Each thread should use its own instance of DbContext. This is crucial because DbContext is not thread-safe, and using it from multiple threads can lead to unpredictable behavior and data corruption. For web applications, this typically means using dependency injection to configure the DbContext with a scoped lifetime, ensuring a new instance per request.

What are the best practices for handling exceptions in EF Core?

Best practices for handling exceptions in EF Core include:

  • Catching specific exceptions like DbUpdateConcurrencyException and DbUpdateException to handle concurrency conflicts and update errors, respectively.
  • Using try-catch blocks around database operations to manage exceptions gracefully.
  • Logging exceptions for debugging and monitoring purposes.
  • Implementing retry logic for transient faults, possibly using the built-in support for it in EF Core.

How can you optimize bulk insert operations in EF Core?

To optimize bulk insert operations in EF Core:

  • Consider using third-party libraries like EF Core.BulkExtensions, which offer optimized bulk operations.
  • Reduce change tracking overhead by calling ChangeTracker.AutoDetectChangesEnabled = false before adding entities to the context.
  • Batch insert operations should be done in reasonable chunks to avoid overwhelming the database.
  • For maximum efficiency, use raw SQL for bulk inserts when dealing with a very large number of records.

What strategies can you employ to manage large models in EF Core?

Strategies for managing large models in EF Core include:

  • Splitting the model into multiple DbContext classes, each handling a subset of the model, to improve maintainability and performance.
  • Using bounded contexts to separate different areas of the application logically.
  • Implementing a repository and unit of work patterns to abstract and manage data operations, making the data access layer more manageable.

How do you implement soft delete functionality in EF Core?

Soft delete can be implemented in EF Core by adding a flag (e.g., IsDeleted) to entities to mark them as deleted. You can then use Global Query Filters to filter out entities marked as deleted from all queries automatically. When deleting an entity, instead of removing it, set the flag to true and update the entity.

What are some common performance pitfalls in EF Core, and how can you avoid them?

Common performance pitfalls in EF Core include:

  • Overusing eager loading leads to unnecessarily large data retrieval. Use it judiciously and prefer explicit or lazy loading when appropriate.
  • Not using .AsNoTracking() for read-only queries, resulting in unnecessary change tracking overhead.
  • Performing bulk updates and inserts without optimization. Use bulk operation techniques or third-party libraries.
  • Avoid these pitfalls by profiling and monitoring your application, understanding the data access patterns, and choosing the most efficient data loading and modification strategies.

How do you migrate from EF 6 to EF Core?

Migrating from EF 6 to EF Core involves:

  • Assessing compatibility since EF Core may not support all EF 6 features. Review the EF Core documentation for feature compatibility.
  • Updating the data model to align with EF Core conventions and features.
  • Rewrite the data access code to use EF Core APIs and adjust for any differences in behavior or functionality.
  • Generating a new migration in EF Core to create or update the database schema.
  • Testing extensively to ensure the application behaves as expected with EF Core.

Discuss strategies for handling large datasets in EF Core.

  • One strategy is to use pagination, where you fetch data in chunks rather than all at once, using methods like Skip() and Take().
  • Another approach is to optimize your queries by using appropriate indexing, including covering indexes, to speed up data retrieval.
  • Utilizing asynchronous methods (ToListAsync() instead of ToList()) can also improve performance by allowing parallel execution of database queries.

How do you manage complex queries using EF Core?

  • Break down complex queries into smaller, manageable parts, possibly using method chaining or query composition techniques.
  • Utilize raw SQL queries or stored procedures for queries that are too complex to be efficiently expressed using LINQ.
  • Consider using database views or materialized views to simplify complex queries and improve performance.

Explain how to implement repository and unit of work patterns with EF Core.

  • Implement a generic repository interface for common CRUD operations, abstracting away EF Core specifics.
  • Implement a unit of work class to coordinate multiple repository operations within a single transaction.
  • Inject these repositories and unit of work instances into your application services to keep your business logic decoupled from data access concerns.

What are some common pitfalls in EF Core, and how can you avoid them?

  • N+1 query problem: Avoid it by using eager loading (Include()), explicit loading (Load()), or projection (Select()).
  • Ignorance of database interactions: Understand how LINQ queries translate into SQL to write efficient queries and optimize performance.
  • Failure to handle concurrency: Use appropriate concurrency control mechanisms like optimistic concurrency or row versioning.

How do you use EF Core in a multi-threaded environment?

  • Use a separate instance of DbContext per thread or per logical unit of work.
  • Avoid sharing DbContext instances across threads, as they are not thread-safe.
  • Use async/await patterns for asynchronous database operations to prevent blocking threads.

What are the best practices for securing data in EF Core?

  • Implement proper authentication and authorization mechanisms in your application to control access to data.
  • Use parameterized queries or stored procedures to prevent SQL injection attacks.
  • Encrypt sensitive data at rest and during transmission using appropriate encryption algorithms.

How do you handle multi-tenancy in EF Core?

  • Add a TenantId column to your tables to associate each record with a specific tenant.
  • Filter queries based on the current tenant, either explicitly in each query or through middleware.
  • Use a separate database schema or database per tenant, if necessary, to completely isolate tenant data.

Discuss the use of Value Converters in EF Core.

  • Value converters allow mapping between types in the database and types in the application.
  • They can be used to handle scenarios like mapping enum values to strings, storing JSON data in a text column, or converting between different date/time representations.
  • Implement custom value converters when the built-in converters don’t meet your requirements.

What tools and extensions are available for EF Core development?

  • Visual Studio provides built-in support for EF Core development, including tools for model creation, migrations, and database management.
  • dotnet-ef command-line tool offers commands for managing database migrations, generating database scripts, and more.
  • EF Core Power Tools extension for Visual Studio provides additional features such as reverse engineering an existing database into EF Core models.

Under the Hood EF Core Interview Questions and Answers

In this section, I will give the List of Under the Hood Entity Framework Core (EF Core) Interview Questions and Answers.

How does EF Core generate SQL from LINQ queries?

EF Core uses a query provider that translates LINQ expressions into SQL queries. The process involves parsing the LINQ expression tree, translating it into a model-specific query expression tree that represents the query in terms of the underlying database model, and then generating the corresponding SQL statement. This process allows EF Core to support a wide range of database systems by abstracting the specifics of SQL generation for each database provider.

What is the Change Tracker in EF Core, and how does it work?

The Change Tracker in EF Core is responsible for keeping track of all the changes made to the entities since they were loaded from the database. It does this by taking a snapshot of entity states when they are first retrieved and then comparing the current state to this snapshot upon calling SaveChanges(). Based on this comparison, EF Core determines which entities must be inserted, updated, or deleted in the database.

Can you explain the concept of Shadow State in EF Core?

Shadow State in EF Core refers to properties that are not defined in the entity class itself but are nevertheless part of the model and managed by EF Core. These properties exist only in the EF Core model and are stored in the database, making them useful for fields like foreign keys or audit columns that don’t need to be exposed to the entity class. Shadow properties are accessed and modified using the EF Core API, such as Entry(entity).Property(“ShadowPropertyName”).CurrentValue.

How does EF Core handle database migrations and schema updates?

EF Core handles database migrations, and schema updates through a feature called Migrations. Developers define changes to the model, and EF Core generates code that can apply these changes to the database schema. Migrations can be added, removed, or modified manually if needed. Migrations can be applied programmatically via the DbContext.Database.Migrate() method or through command-line tools, allowing for controlled schema evolution across different environments.

What mechanisms does EF Core use to Optimize Query Performance?

EF Core optimizes query performance through several mechanisms, including:

  • Query Caching: EF Core caches compiled query plans to avoid re-compiling the same query.
  • Batching: EF Core batches multiple operations into a single database command when possible, reducing round trips to the database.
  • No-Tracking Queries: For read-only scenarios, queries can be executed without tracking changes to the entities, reducing overhead.
  • Eager Loading: Allows specifying related data to be loaded upfront, reducing the number of separate queries required.

Explain how EF Core uses both Lazy Loading and Eager Loading.

EF Core supports both lazy loading and eager loading for loading related data:

  • Lazy Loading: Related data is loaded on-demand when the navigation property is accessed for the first time. This is achieved by making navigation properties virtual and using proxy entities or interceptors. Lazy loading can lead to the N+1 query problem if not used carefully.
  • Eager Loading: Related data is loaded upfront in the initial query using the Include method. This approach is efficient when you know you will need the related data for every entity being loaded, as it reduces the number of queries made to the database.

What are compiled queries in EF Core, and when would you use them?

Compiled queries in EF Core are queries that have been compiled into a delegate for reuse. This feature is useful for queries that are executed frequently with different parameters. By compiling a query once and reusing it, you avoid the cost of query compilation on subsequent executions, improving performance. Compiled queries are defined using the EF.CompileQuery and EF.CompileAsyncQuery methods.

How does EF Core manage transactions across multiple database operations?

EF Core manages transactions by wrapping multiple database operations in a single transaction scope. By default, EF Core uses a transaction for each SaveChanges() call. For more control, developers can use the BeginTransaction() method to start a transaction explicitly, execute multiple operations, and then commit or roll back the transaction using the Commit() or Rollback() methods, ensuring atomicity of the operations.

Discuss how EF Core supports multiple database providers.

EF Core supports multiple database providers through an extensible provider model. Each provider implements the interfaces defined by EF Core to translate operations, queries, and updates into database-specific SQL and functionality. This design allows EF Core to interact with different types of databases, such as SQL Server, SQLite, PostgreSQL, and others, by simply changing the provider in the application configuration without altering the application code.

What are the limitations of EF Core?

  • EF Core lacks some features compared to Entity Framework 6, such as no support for lazy loading of related data by default, no built-in support for many-to-many relationships without explicit join entities, and limited support for complex types.
  • EF Core may have performance issues with complex queries compared to raw SQL queries or stored procedures.
  • Some database-specific features may not be fully supported or optimized in EF Core.

Discuss how EF Core works with Asynchronous Programming.

  • EF Core provides asynchronous versions of its database operations, such as ToListAsync() or SaveChangesAsync().
  • Asynchronous programming allows non-blocking execution of database operations, improving the scalability and responsiveness of applications.
  • When using asynchronous methods, EF Core utilizes the underlying database provider’s asynchronous APIs to perform I/O operations asynchronously.

What is the Entity Framework Core Query Pipeline?

  • The EF Core query pipeline is the internal mechanism responsible for translating LINQ queries into SQL queries that can be executed against the database.
  • It includes components for query composition, translation of LINQ expressions to SQL, materialization of query results, and execution of SQL commands.
  • Developers can extend or customize the query pipeline through interceptors or query filters to modify query behavior or add additional processing.

How does EF Core handle caching?

  • EF Core performs caching at various levels to improve performance.
  • Query results, entity instances, and metadata are cached to reduce database round-trips and improve application responsiveness.
  • EF Core supports query result caching, which allows the caching of query results for a specified duration or until the underlying data changes.
  • Developers can control caching behavior through configuration options or explicit caching mechanisms.

Explain how transactions work in EF Core.

  • EF Core supports transactions to ensure data consistency and integrity when performing multiple database operations.
  • Transactions can be managed explicitly using TransactionScope or BeginTransaction() methods on the DbContext or DbTransaction objects.
  • EF Core automatically enlists ambient transactions when running within a transaction scope, allowing multiple database operations to participate in the same transaction.
  • Transactions can be committed or rolled back using Commit() or Rollback() methods, respectively.

What are interceptors in EF Core, and how do you use them?

  • Interceptors are a feature of EF Core that allows you to intercept and modify database commands and results at various points in the query and save pipelines.
  • Interceptors can be used for logging, performance monitoring, security, and auditing purposes.
  • They can intercept commands such as queries, inserts, updates, and deletes, as well as the results returned by these commands.
  • Interceptors are implemented by creating classes that derive from DbCommandInterceptor or DbConnectionInterceptor and overriding their methods to add custom logic.
How do you extend EF Core functionality with custom services?
  • EF Core allows you to extend its functionality by registering custom services and interceptors.
  • You can register custom services with the EF Core dependency injection container during application startup.
  • Custom services can be used to implement custom query providers, value converters, model conventions, and more.
  • You can also use third-party libraries or packages to extend EF Core functionality, such as EF Core Power Tools or EF Core community extensions.

Discuss the future developments and roadmap for EF Core.

  • The EF Core team regularly releases updates and improvements to the framework, including new features, performance enhancements, and bug fixes.
  • The roadmap for EF Core includes plans for supporting additional database providers, improving performance, enhancing tooling support, and adding new features requested by the community.
  • The EF Core team actively engages with the community through GitHub discussions, user surveys, and feedback channels to prioritize future developments and address user needs.

Preparing answers for these questions will not only help you get ready for an interview but will also deepen your understanding of EF Core. Remember, practical experience and familiarity with the latest version of EF Core will significantly enhance your responses.

In the next article, I will discuss the Top 50 ASP.NET Core Basic Interview Questions and Answers. In this article, I provided the list of Frequently Asked Top 100 Entity Framework (EF) Core Interview Questions and Answers. I hope you enjoy this article on Entity Framework (EF) Core Interview Questions and Answers. If you want to share any questions and answers, please put them in the comment section, which will benefit others. I hope you enjoy this Top 100 Entity Framework (EF) Core Interview Questions and Answers article.

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