Top 50 Entity Framework Core Interview Questions and Answers

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Top 50 Entity Framework Core Interview Questions and Answers

In this article, I will discuss the most frequently asked Top 50 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 50 Entity Framework (EF) Core Interview Questions and Answers. For easy understanding, I have categorized the interview questions and answers into three sections. They are as follows:

  • Basic Entity Framework Core (EF Core) Interview Questions and Answers
  • Intermediate Entity Framework Core (EF Core) I Interview Questions and Answers
  • Advanced Entity Framework Core (EF Core) I Interview Questions and Answers

Basic Entiy EF Core Interview Questions and Answers

In this section, I will give the List of Basic Entity Framework (EF) Core Interview Questions and Answers. These questions can be asked to anyone including students and freshers.

1. What is Entity Framework Core?

Entity Framework Core (EF Core) is an open-source, lightweight, extensible, and cross-platform object-relational mapper (ORM) developed by Microsoft for .NET applications. It enables developers to interact with databases using .NET objects, eliminating the need for most of the data-access code typically required. EF Core provides high performance and supports LINQ queries, change tracking, migrations, and more, making database operations easier and more efficient.

2. How does EF Core work?

EF Core operates by mapping our application’s classes (entities) to database tables and their properties to table columns. It tracks changes made to these entities and, upon invoking the SaveChanges() method, translates these changes into SQL commands to update the database accordingly. EF Core can automatically generate SQL queries for CRUD operations and can also be configured to work with raw SQL when needed. It uses a DbContext to manage database connections and operations, ensuring seamless interaction between the application and the database.

3. What are the main components of EF Core?

The primary components of EF Core include:

  • DbContext: Acts as a bridge between our domain classes and the database, managing entity instances and database connections.
  • DbSet: Represents a collection of entities of a specific type, allowing for querying and saving instances.
  • Model: Defines the structure of the data, including entities, relationships, and configurations.
  • Change Tracking: Monitors changes made to entities to determine how to persist them to the database.
  • Querying: Enables retrieval of data using LINQ (Language Integrated Query).
  • Migrations: Manage schema changes in the database to match changes in the data model.
4. What are Migrations in EF Core, and why are they useful?

Migrations in EF Core are a way to incrementally update the database schema to match the application’s data model while preserving existing data. They allow developers to apply changes to the database structure without manually writing SQL scripts. Migrations can be automatically generated based on changes in the entity classes and can be applied programmatically or via command-line tools. They automate schema changes using Add-Migration and Update-Database commands, minimizing the need for manual SQL scripting.

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

The Code-First approach in EF Core allows developers to define the data model using C# classes without an existing database. EF Core uses these classes to generate the database schema. This approach is beneficial for developers who prefer to work within code rather than using database design tools. It also integrates well with version control systems, as changes to the data model can be managed through migrations, ensuring that the database syncs alongside the application code.

6. What is the difference between Entity Framework and EF Core?

Entity Framework (EF) is the original ORM developed by Microsoft for the .NET Framework, whereas EF Core is a modern, lightweight, and cross-platform rewrite designed for .NET Core and later versions. EF Core offers several improvements over EF, including better performance, support for non-relational databases, improved LINQ translation, optimization for asynchronous operations, and new features like shadow properties and global query filters. Additionally, EF Core is more modular and extensible, allowing developers to include only the necessary components for their applications. EF Core is also cross-platform, meaning it works on Windows, Linux, and macOS.

7. What are Shadow Properties in EF Core?

Shadow properties are properties that are part of the EF Core model but are not defined in the entity class itself and mapped to the database. These properties exist only in the EF Core metadata and are stored in the database. They are useful for scenarios where certain data needs to be tracked or used by EF Core without being exposed through the entity’s API, such as audit information (CreatedAt, UpdatedBy) or foreign keys without exposing them in the entity class. These can be configured using the Fluent API and accessed through the EF Core API.

8. How does EF Core Handle Transactions?

EF Core manages transactions to ensure data integrity by grouping multiple database operations into a single atomic unit of work. These ensure atomic operations for multiple database changes. By default, a call to SaveChanges() or SaveChangesAsync() is wrapped in a transaction. For more control, developers can manually begin, commit, or rollback transactions using the Database.BeginTransaction(), Commit(), and Rollback() methods are provided by the DbContext. EF Core also allows transactions to span across multiple contexts or even multiple databases.

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

Lazy loading is a pattern where related data is loaded from the database only when it is specifically accessed rather than being loaded upfront with the initial query. In EF Core, lazy loading can be implemented by installing Microsoft.EntityFrameworkCore.Proxies package and enabling it in the DbContext configuration using the UseLazyLoadingProxies() method. Additionally, navigation properties in the entity classes must be declared as virtual so that EF Core can create proxy classes to override these properties and insert the loading logic.

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

Eager loading is a pattern where related data is loaded as part of the initial query using methods like Include(). This approach fetches all the required data in a single query, which can improve performance by reducing the number of database round-trips. In contrast, lazy loading defers the loading of related data until it is accessed, potentially resulting in multiple queries being sent to the database. Eager loading is beneficial when you know you will need the related data immediately, while lazy loading can be more efficient when related data is only occasionally needed.

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

Several strategies can enhance EF Core performance:

  • Use AsNoTracking(): For read-only queries, disable change tracking to reduce overhead.
  • Optimize Queries: Select only necessary columns and avoid N+1 query issues by appropriately using eager or explicit loading.
  • Batch Operations: Perform bulk inserts, updates, or deletes in batches to minimize database round-trips.
  • Caching: Implement query result caching or use compiled queries to reuse execution plans.
  • Indexing: Ensure that database tables have appropriate indexes to speed up query execution.
  • Use Raw SQL and Stored Procedure: For complex or performance-critical queries, use raw SQL or Stored Procedure to use database-specific optimizations.
  • DbContext Pooling: Reuse DbContext instances to reduce the overhead of creating and disposing of contexts.
12. How do you define relationships in EF Core?

Relationships in EF Core are defined through navigation properties in entity classes and can be configured using data annotations or the Fluent API methods. The main types of relationships are:

  1. One-to-One: Each instance of an entity is related to exactly one instance of another entity. Configured using HasOne() and WithOne() in the Fluent API.
  2. One-to-Many: One entity instance is related to multiple instances of another entity. Represented by a collection navigation property on one side and a reference on the other, configured using HasMany() and WithOne().
  3. Many-to-Many: Multiple instances of one entity are related to multiple instances of another entity. EF Core manages this by creating a join table, which can be explicitly defined if needed.
13. What is a DbContext?

A DbContext in EF Core represents a session with the database, providing the necessary APIs to interact with the data. It manages entity objects, handles database connections, tracks changes, and performs CRUD operations. It provides methods for querying, saving, and tracking changes to entities, as well as managing transactions. That means it serves as a bridge between application models and the database. The DbContext is configured with options such as the database provider and connection string and typically includes DbSet properties for each entity type in the model.

14. What are Entities in EF Core?

Entities in EF Core are classes that represent the data structure of our application. Each entity corresponds to a table in the database, and the properties of the class map to the columns of that table. Entities are tracked by the DbContext for changes, enabling EF Core to perform insert, update, and delete operations based on the modifications made to the entity instances.

Intermediate EF Core Interview Questions and Answers

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

15. How do you use Fluent API in EF Core?

The Fluent API in EF Core provides a way to configure the data model in a code-based, fluent manner, allowing for more complex configurations that cannot be achieved with data annotations, such as complex relationships, composite keys, constraints, indexes, etc. To use the Fluent API:

  • Override OnModelCreating: In your DbContext class, override the OnModelCreating(ModelBuilder modelBuilder) method.
  • Configure Entities and Relationships: Use the modelBuilder to define entity configurations, including properties, keys, relationships, indexes, and more.

Example:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .HasKey(b => b.BlogId);

    modelBuilder.Entity<Blog>()
        .Property(b => b.Url)
        .IsRequired()
        .HasMaxLength(500);

    modelBuilder.Entity<Post>()
        .HasOne(p => p.Blog)
        .WithMany(b => b.Posts)
        .HasForeignKey(p => p.BlogId);
}
16. Explain the role of DbSet in EF Core.

A DbSet<T> represents a collection of entities of a specific type within the DbContext. It provides the primary API (methods) for querying and interacting with entities in the database. Through DbSet, developers can perform operations such as adding, removing, updating, and retrieving entities. Each DbSet typically corresponds to a table or view in the database and is exposed as a property in the DbContext.

17. 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 by using the HasMany() and WithOne() methods. Assuming we have Blog and Post entities where one Blog has many Posts. To configure a one-to-many relationship using the Fluent API in EF Core, we need to override the OnModelCreating method and write the following code:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .HasMany(b => b.Posts)
        .WithOne(p => p.Blog)
        .HasForeignKey(p => p.BlogId);
}

This configuration sets up a one-to-many relationship where a Blog has many Posts, and each Post is associated with one Blog via the BlogId foreign key.

18. How do you Track Changes in EF Core?

EF Core uses a change tracking mechanism to monitor changes made to entity instances. When an entity is retrieved from the database, EF Core keeps a snapshot of its original state. As properties of the entity are modified, EF Core detects these changes by comparing the current state to the snapshot. Upon calling SaveChanges(), EF Core generates the appropriate SQL commands (insert, update, delete) to persist the changes to the database. Change tracking can be configured as automatic or disabled (using .AsNoTracking()) depending on the application’s needs.

19. Discuss the AsNoTracking() method.

The AsNoTracking() method in EF Core executes queries without tracking the returned entities in the DbContext. This is beneficial for read-only operations where change tracking is unnecessary, as it reduces memory usage and improves performance by eliminating the overhead associated with tracking.

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. To use it, append .AsNoTracking() to your query:

var blogs = context.Blogs.AsNoTracking().ToList();

This retrieves the list of blogs without tracking them for changes, making the operation more efficient for scenarios where updates are not required.

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

EF Core allows executing raw SQL queries for scenarios where LINQ is insufficient or when specific SQL features are needed. To perform a raw SQL query that returns entities, use the FromSqlRaw or FromSqlInterpolated methods on a DbSet:

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

For executing commands that do not return entities, use the ExecuteSqlRaw or ExecuteSqlInterpolated methods:

int affectedRows = context.Database.ExecuteSqlRaw(“UPDATE Blogs SET Name = {0} WHERE BlogId = {1}”, newName, blogId);

These methods provide the flexibility to interact directly with the database using SQL while still benefiting from EF Core’s context management.

21. 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 primary states are:

  • Added: The entity is new and should be inserted into the database upon SaveChanges().
  • Unchanged: The entity has not been modified since it was retrieved and does not require any action.
  • Modified: The entity has been modified and requires an update in the database.
  • Deleted: The entity has been marked for deletion and will be removed from the database.
  • Detached: The entity is not being tracked by the DbContext and has no state.

Understanding entity states is crucial for managing how changes to entities are persisted in the database.

22. What is a Composite Key, and how can you configure it in EF Core?

A composite key is a primary key that consists of two or more columns in a database table, used together to uniquely identify a row. In EF Core, composite keys can be configured using the Fluent API by specifying the properties that make up the key within the OnModelCreating method. Within this method, use the HasKey() method on the EntityTypeBuilder object to specify the properties that make up the composite key. For example:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<OrderItem>()
        .HasKey(oi => new { oi.OrderId, oi.ProductId });
}

In this example, the OrderItem entity has a composite key consisting of OrderId and ProductId, ensuring that each combination of these two properties is unique in the table.

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

EF Core supports three inheritance mapping strategies:

  • TPH (Table Per Hierarchy): This strategy involves using a single database table to store the data for all types involved in an inheritance hierarchy. A discriminator column is used to differentiate between the types. This approach is efficient for querying because it avoids joins but can lead to sparse tables with many nullable columns.
  • 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 derived types.
  • TPC (Table Per Concrete Class): Each concrete class in the hierarchy is mapped to its own table, including all properties from the base classes. This approach can eliminate the need for joins and discriminator columns but can lead to data duplication across tables.

Note: EF Core 5.0 and later versions support TPH and TPT strategies, with TPC introduced in EF Core 7.0.

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

Best practices for handling exceptions in EF Core include:

  • Catch Specific Exceptions: Handling specific exceptions like DbUpdateConcurrencyException and DbUpdateException to handle concurrency conflicts and update errors, respectively.
  • Use Try-Catch Blocks: Encapsulate database operations within try-catch blocks to manage exceptions gracefully.
  • Log Exceptions: Log detailed error information for debugging and monitoring purposes.
  • Provide User-Friendly Messages: Avoid exposing technical details to users; instead, show meaningful messages.
  • Validate Data Before Operations: Perform validation to prevent exceptions due to invalid data.

Example:

try
{
    context.SaveChanges();
}
catch (DbUpdateConcurrencyException ex)
{
    // Handle concurrency conflict
   logger.LogError(ex, "An error occurred while updating the database.");
}
catch (DbUpdateException ex)
{
    // Handle database update errors’
    logger.LogError(ex, "An error occurred while updating the database.");
}
25. How does EF Core Implement Optimistic Concurrency Control?

Concurrency control in EF Core ensures that when multiple users or processes attempt to update the same entity, data conflicts are prevented or handled gracefully. EF Core provides optimistic concurrency control using concurrency tokens.

To configure concurrency control:

  • Mark a property as a concurrency token using the [ConcurrencyCheck] attribute or the Fluent API.
  • When updating an entity, EF Core checks if the concurrency token has changed to detect conflicts.

Example (Fluent API):

public class Product
{
    public int ProductId { get; set; }
    public string Name { get; set; }
    
    [Timestamp]
    public byte[] RowVersion { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Product>()
        .Property(p => p.RowVersion)
        .IsRowVersion();
}

In this example, the RowVersion property is marked as a concurrency token. EF Core includes this column in the WHERE clause of the UPDATE query. If the token has changed since the entity was loaded, a DbUpdateConcurrencyException will be thrown, allowing you to handle the conflict appropriately.

26. How can you optimize bulk insert operations in EF Core?

To optimize bulk insert operations in EF Core:

  • Use Third-Party Libraries: Use libraries like EFCore.BulkExtensions that provide optimized bulk insert methods.
  • Disable Change Tracking: Temporarily disable change tracking by setting ChangeTracker.AutoDetectChangesEnabled = false to reduce overhead.
  • Batch Inserts: Insert entities in batches rather than one at a time to minimize database round-trips.
  • Use Raw SQL: For very large datasets, execute raw SQL bulk insert commands to maximize efficiency.

Example using a third-party library: context.BulkInsert(entities);

These approaches help in efficiently inserting large numbers of records with minimal performance impact.

27. How do you implement Soft Delete functionality in EF Core?

Soft delete allows entities to be marked as deleted without physically removing them from the database. To implement soft delete in EF Core:

  • Add a Deletion Flag: Include a property in your entity (e.g., IsDeleted).
  • Configure Global Query Filters: Use the Fluent API to exclude entities where IsDeleted is true from queries.

Example:

public class Blog
{
    public int BlogId { get; set; }
    public string Name { get; set; }
    public bool IsDeleted { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().HasQueryFilter(b => !b.IsDeleted);
}

Override Delete Operations: Instead of removing entities, set the IsDeleted flag to true.

var blog = context.Blogs.Find(blogId);
blog.IsDeleted = true;
context.SaveChanges();

This approach ensures that deleted entities are excluded from query results but remain in the database for potential recovery or auditing.

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

Common performance issues in EF Core include:

  • N+1 Query Problem: Occurs when multiple separate queries are executed for related data. Solution: Use eager loading with Include() or ThenInclude() to load related data in a single query.
  • Unnecessary Change Tracking: Tracking entities when not needed increases overhead. Solution: Use AsNoTracking() for read-only queries.
  • Large Data Retrieval: Fetching more data than necessary can slow down performance. Solution: Select only the required columns and use projection with Select().
  • Inefficient Queries: Poorly constructed LINQ queries can result in suboptimal SQL. Solution: Optimize LINQ queries and review generated SQL using logging or profiling tools.
  • Excessive Database Round-Trips: Making multiple calls to the database instead of batching operations. Solution: Batch operations where possible and minimize the number of database calls.
  • Lack of Indexes: Missing indexes on frequently queried columns can degrade performance. Solution: Ensure appropriate indexing in the database schema.

By being aware of these issues and applying best practices, you can significantly enhance the performance of applications using EF Core.

29. Discuss strategies for handling large datasets in EF Core.

When dealing with large datasets in EF Core, consider the following strategies:

  • Pagination: Retrieve data in manageable chunks using methods like Skip() and Take() to limit the amount of data loaded at once.
  • Asynchronous Queries: Use asynchronous methods (e.g., ToListAsync()) to avoid blocking the main thread and improve scalability.
  • Projection: Select only the necessary fields instead of loading entire entities, reducing memory usage.
  • Indexing: Ensure that the database has appropriate indexes to speed up data retrieval operations.
  • Batch Processing: Process data in batches to reduce the number of database operations and manage resource usage effectively.

Implementing these strategies can help efficiently manage and process large volumes of data without compromising application performance.

Advanced Entity 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.

30. How do you manage complex queries using EF Core?

Managing complex queries in EF Core can be achieved through:

  • Query Composition: Break down complex queries into smaller, reusable parts using LINQ method chaining.
  • Raw SQL Queries: Use FromSqlRaw() or ExecuteSqlRaw() to execute complex SQL directly when LINQ is insufficient.
  • Stored Procedures: Use stored procedures for complex data operations and call them from EF Core.
  • Database Views: Create views in the database to encapsulate complex joins or aggregations and map them to entity types.
  • Expression Trees: Build dynamic queries using expression trees for scenarios requiring flexible query structures.

These techniques provide flexibility in constructing and executing complex data retrieval and manipulation operations while maintaining the benefits of EF Core’s ORM capabilities.

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

Best practices for securing data in EF Core include:

  • Use Parameterized Queries: Avoid SQL injection by using parameterized queries or LINQ, which inherently uses parameters.
  • Implement Authentication and Authorization: Ensure that only authorized users can access or modify data through proper authentication mechanisms.
  • Encrypt Sensitive Data: Encrypt sensitive information both at rest and in transit using appropriate encryption algorithms.
  • Validate Input: Perform input validation to prevent malicious data from being processed.
  • Limit Database Permissions: Grant the least privileges necessary to the database user accounts used by the application.
  • Use Secure Connection Strings: Protect connection strings by storing them securely, such as in environment variables or secure vaults, and avoid hardcoding them.
  • Enable SSL/TLS: Ensure that database connections are encrypted using SSL/TLS to protect data during transmission.

Implementing these practices helps protect data integrity and confidentiality when using EF Core.

32. How do you handle multi-tenancy in EF Core?

Handling multi-tenancy in EF Core involves strategies to isolate data for different tenants within the same application. Common approaches include:

  • Shared Database with Tenant Identifier: Add a TenantId column to all relevant tables to associate records with specific tenants. Use global query filters to automatically filter data based on the current tenant.
  • Separate Schemas per Tenant: Use separate database schemas for each tenant within the same database, isolating data at the schema level.
  • Separate Databases per Tenant: Provision individual databases for each tenant, providing complete isolation but increasing management complexity.

Example of using a shared database with a tenant identifier and global query filters:

public class Blog
{
    public int BlogId { get; set; }
    public string Name { get; set; }
    public string TenantId { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().HasQueryFilter(b => b.TenantId == _currentTenantId);
}

This ensures that all queries against the Blog entity automatically include the tenant filter, maintaining data isolation.

33. How does EF Core generate SQL from LINQ queries?

EF Core translates LINQ queries into SQL using a query provider that parses the LINQ expression trees. The process involves:

  • Parsing: The LINQ expression is parsed into an expression tree, representing the query structure.
  • Translation: The expression tree is translated into a database-specific query expression based on the database provider’s capabilities.
  • SQL Generation: The translated expression is converted into the corresponding SQL statement that can be executed by the database.

This translation process allows developers to write type-safe queries using LINQ, while EF Core handles the generation of optimized SQL queries tailored to the target database system.

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

The Change Tracker in EF Core is a component responsible for monitoring changes to entities within the DbContext. It keeps track of the original and current values of entity properties, determining which entities are added, modified, or deleted. When SaveChanges() is invoked, the Change Tracker uses this information to generate the appropriate SQL commands to persist these changes to the database. The Change Tracker operates based on entity states, ensuring that only the necessary updates are sent to the database.

35. What mechanisms does EF Core use for optimizing query performance?

EF Core employs several mechanisms to optimize query performance:

  • Query Caching: EF Core caches compiled query plans to avoid recompiling frequently used queries.
  • Batching: Multiple database operations are batched into a single command to reduce round-trips.
  • No-Tracking Queries: Queries that do not require change tracking are executed with reduced overhead.
  • Eager Loading: Preloading related data using Include() reduces the number of separate queries.
  • Compiled Queries: Precompiling queries using EF.CompileQuery for repeated execution with different parameters.
  • Index Utilization: Leveraging database indexes through optimized query construction.

These optimizations help minimize latency, reduce resource consumption, and enhance overall application performance.

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

Compiled queries in EF Core are preprocessed LINQ queries that have been compiled into executable delegates for reuse. They can significantly improve performance for queries that are executed repeatedly with different parameters by eliminating the need to reparse and retranslate the LINQ expression trees each time.

Example of defining a compiled query:

private static readonly Func<MyDbContext, string, IQueryable<Blog>> _getBlogsByName =
    EF.CompileQuery((MyDbContext context, string name) =>
        context.Blogs.Where(b => b.Name == name));

Using the compiled query: var blogs = _getBlogsByName(context, “EF Core”).ToList();

Compiled queries are beneficial in high-performance scenarios where the same query structure is executed multiple times with varying parameters.

37. How does EF Core manage transactions across multiple database operations?

EF Core manages transactions by grouping multiple database operations into a single transaction scope. By default, a call to SaveChanges() wraps the changes in a transaction. For operations that span multiple SaveChanges() calls or require explicit transaction boundaries, developers can use the Database.BeginTransaction() method to start a transaction, perform multiple operations, and then commit or rollback the transaction as needed. This ensures atomicity, consistency, isolation, and durability (ACID) across all operations within the transaction.

Example:

using (var transaction = context.Database.BeginTransaction())
{
    try
    {
        // Perform multiple operations
        context.Blogs.Add(new Blog { Name = "Blog1" });
        context.SaveChanges();

        context.Posts.Add(new Post { Title = "Post1", BlogId = blogId });
        context.SaveChanges();

        transaction.Commit();
    }
    catch
    {
        transaction.Rollback();
    }
}

This approach ensures that all operations within the transaction are either committed together or rolled back in case of an error, maintaining data integrity.

38. Discuss how EF Core supports multiple database providers.

EF Core is designed to be database-agnostic, supporting multiple database providers through an extensible provider model. Each database provider (e.g., SQL Server, SQLite, PostgreSQL) implements the necessary interfaces and functionalities to translate EF Core operations into database-specific SQL commands and features. Developers can switch between different database providers by changing the configuration in the DbContext options, allowing the same application code to work with various database systems without modification.

Example configuration for SQL Server:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.UseSqlServer("YourConnectionString");
}

And for SQLite:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.UseSqlite("YourConnectionString");
}

This flexibility enables EF Core to be used in diverse environments and with different database technologies.

39. Discuss how EF Core works with Asynchronous Programming.

EF Core provides asynchronous methods for all database operations, promoting non-blocking I/O operations and enhancing application scalability and responsiveness. Asynchronous methods, such as ToListAsync(), FirstOrDefaultAsync(), and SaveChangesAsync(), allow applications to perform database operations without blocking the main thread, which is especially beneficial in web applications and UI applications where responsiveness is critical.

Example: var blogs = await context.Blogs.ToListAsync();

By using asynchronous programming patterns, EF Core enables applications to handle multiple concurrent operations efficiently, improving overall performance and user experience.

40. How Does EF Core Handle Caching?

EF Core implements caching mechanisms to enhance performance by reducing redundant database queries and minimizing the overhead of data retrieval. Key caching features include:

  • First-Level Cache: Each DbContext instance maintains a first-level cache, storing entities that have been retrieved or tracked. This cache ensures that repeated queries within the same context instance return the same entity instances, preventing unnecessary database hits.
  • Compiled Query Cache: EF Core caches compiled query plans for LINQ queries, reducing the cost of translating queries into SQL for repeated executions.

Developers can use these caching mechanisms to optimize data access patterns, improve response times, and reduce database load.

41. 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.
42. Explain how to use Stored Procedures with EF Core.

EF Core allows executing stored procedures for both querying and non-query operations.

For Queries: Use FromSqlRaw() or FromSqlInterpolated() on a DbSet to map results to entities.

var blogs = context.Blogs
                   .FromSqlRaw("EXEC GetBlogsByAuthor @Author={0}", authorName)
                   .ToList();

For Non-Queries: Use ExecuteSqlRaw() or ExecuteSqlInterpolated() for operations like insert, update, or delete.

context.Database.ExecuteSqlRaw("EXEC UpdateBlogName @Id={0}, @Name={1}", id, newName);

Note: Always use parameterization to prevent SQL injection. Ensure the stored procedure’s result matches the entity structure when querying.

43. 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 high-throughput scenarios, such as web applications

When to Use:

  • Applications that create and dispose of DbContext frequently.
  • Scenarios where the overhead of creating DbContext instances is significant.

Configuration Example:

services.AddDbContextPool<MyDbContext>(options =>
    options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

Benefits:

  • Improved performance through reduced allocation costs.
  • Better resource utilization by reusing existing contexts.
44. How do Global Query Filters work in EF Core? Can you provide an example?

Global Query Filters are LINQ predicates applied automatically to all queries for a specific entity type. They are useful for implementing soft delete functionality, multi-tenancy, or filtering data based on some global criteria

Example: Implementing Soft Delete

public class Blog
{
    public int BlogId { get; set; }
    public string Name { get; set; }
    public bool IsDeleted { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().HasQueryFilter(b => !b.IsDeleted);
}

Usage: All queries on Blogs will automatically exclude those where IsDeleted is true.

Ignoring Filters: var allBlogs = context.Blogs.IgnoreQueryFilters().ToList();

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

Owned Entities are types that are part of another entity and do not have their own identity. They are used to model complex value objects. Owned entities are stored in the same table as their owner by default and are useful for grouping related properties.

Example: Address as an Owned Entity

public class Blog
{
    public int BlogId { get; set; }
    public string Name { get; set; }
    
    public Address Address { get; set; }
}

[Owned]
public class Address
{
    public string Street { get; set; }
    public string City { get; set; }
}

Configuration:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().OwnsOne(b => b.Address);
}
46. How does EF Core support database seeding, and why is it useful?

Database seeding in EF Core allows us to populate a database with initial or test data when the database is created or updated via migrations. This feature is useful for providing default data for testing or setting up application prerequisites. To configure seeding, use the HasData method in the OnModelCreating method of the DbContext.

Example: Seeding a list of Blog entities.

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().HasData(
        new Blog { BlogId = 1, Url = "https://example.com/blog1" },
        new Blog { BlogId = 2, Url = "https://example.com/blog2" }
    );
}

Key Points:

  • HasData Method: Used to specify the seed data.
  • Migration Integration: Seed data is inserted during the Update-Database command as part of the migration.
  • Primary Keys Required: Each seeded entity must have a primary key value specified.
47. What are Alternate Keys in EF Core, and how are they configured?

Alternate keys are unique constraints in a database that provide an alternative way of identifying an entity apart from the primary key. They are used when a property (or combination of properties) must have unique values in a table. To configure an alternate key, use the HasAlternateKey method in Fluent API.

Example:

modelBuilder.Entity<User>()
    .HasAlternateKey(u => u.Email); // Ensure Email is unique.

Alternate keys are useful in scenarios like ensuring the uniqueness of email addresses, usernames, or other identifiers that are not primary keys.

48. What are Value Conversions in EF Core, and how do you implement them?

Value Conversions in EF Core allow developers to transform property values when reading from or writing to the database. This is useful for storing data in a different format than used in the application. Suppose we have an Order entity with an OrderStatus enum, and we want to store it as a string in the database.

public enum OrderStatus
{
    Pending,
    Shipped,
    Delivered
}

public class Order
{
    public int OrderId { get; set; }
    public OrderStatus Status { get; set; }
}

Configuration:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Order>()
        .Property(o => o.Status)
        .HasConversion(
            v => v.ToString(),
            v => (OrderStatus)Enum.Parse(typeof(OrderStatus), v));
}

Key Points:

  • Bi-Directional Transformation: Converts the property value when saving to and reading from the database.
  • Built-In Converters: EF Core provides some built-in converters, but custom converters can be implemented as needed.
  • Use Cases: Storing enums as strings, encrypting property values, or transforming complex types.
49. What is Explicit Loading in EF Core, and when would you use it?

Explicit Loading is a technique in EF Core where related data is loaded on-demand after the initial query has been executed. It is useful when we want more control over when and how related data is fetched, avoiding the overhead of eager loading when related data isn’t always needed.

Example: Loading the Posts for a specific Blog entity.

var blog = context.Blogs.Find(blogId);

// Explicitly load related Posts
context.Entry(blog).Collection(b => b.Posts).Load();

Key Points:

  • Control Over Data Loading: Load related data only when necessary.
  • Performance Optimization: Prevents unnecessary data retrieval, improving performance.
  • Methods Used: Load(), LoadAsync(), and Reference() for reference navigation properties.
  • Use Cases: Scenarios where related data is conditionally required based on specific logic or user actions.
50. How does EF Core Handle Many-to-Many Relationships?

In EF Core, a Many-to-Many relationship can be configured either implicitly or explicitly. EF Core automatically creates a join table for Many-to-Many relationships, but it is also possible to define the join table explicitly if additional properties are needed. Starting from EF Core 5.0, EF Core manages many-to-many relationships by creating an implicit join table to link the two entities without requiring an explicit entity class for the join table.

Example: Suppose you have Student and Course entities where each student can enroll in multiple courses, and each course can have multiple students.

public class Student
{
    public int StudentId { get; set; }
    public string Name { get; set; }
    public ICollection<Course> Courses { get; set; }
}
public class Course
{
    public int CourseId { get; set; }
    public string Title { get; set; }
    public ICollection<Student> Students { get; set; }
}

EF Core automatically creates a join table named StudentCourse with StudentId and CourseId as foreign keys. No additional configuration is necessary unless you want to customize the join table.

Preparing answers for these Entity Framework (EF) Core Interview  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 50 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 50 Entity Framework (EF) Core Interview Questions and Answers article.

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