LINQ All Method in C#

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LINQ All Method in C# with Examples

In this article, I will discuss the LINQ All Method in C# with Examples. Please read our previous article, discussing the basics of LINQ Quantifiers Methods in C#. As part of this article, we are going to discuss the following pointers, which are related to the LINQ All Method.

1. What is LINQ All Method in C#?
2. Example to Understand LINQ All Method in C# using Value Type
3. Example to Understand LINQ All Method in C# using String Type
4. LINQ All Method with Complex Type in C#
5. Complex Example to Understand LINQ All Method in C#
6. When To Use LINQ All Method in C#?
7. When Not To Use LINQ All Method in C#?

What is LINQ All Method in C#?

The LINQ All Method in C# checks whether all elements in a sequence satisfy a specified condition. If all the elements satisfy the given condition, it returns true; otherwise, it returns false. It is a part of the System.Linq namespace can be used with any type implementing the IEnumerable<T> or IQueryable<T> collection. There is no overloaded version available for the LINQ All Method. The image below shows that the ALL Extension method takes one predicate as a parameter.

Example to Understand LINQ All Method in C# using Value Type

Let us see an example of understanding LINQ All Method in C# using Method and Query Syntax. The following example returns true as all the elements are greater than 10 in the integer array. No operator is called all in Query Syntax, so we need to use Mixed Syntax.

using System;
using System.Linq;
namespace LINQDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] IntArray = { 11, 22, 33, 44, 55 };

            //Using Method Syntax
            bool ResultMS = IntArray.All(x => x > 10);

            //Using Query Syntax
            bool ResultQS = (from num in IntArray
                            select num).All(x => x > 10);

            Console.WriteLine("Are All Numbers greater than 10? " + ResultMS);
            Console.ReadKey();
        }
    }
}

Output: Are All Numbers greater than 10? True

Note: It’s important to note that the All method returns true for an empty collection. This is consistent with the concept of vacuous truth in mathematical logic, where a universal statement is considered true if it does not apply to any object.

Example to Understand LINQ All Method in C# using String Type

Let us see an example of using the LINQ All Method in C# using String type collection. For a better understanding, please look at the following example, which shows how to use All Method in C# with String type collection. The following example will return false as all the names are not less than five characters.

using System;
using System.Linq;
namespace LINQDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] stringArray = { "James", "Sachin", "Sourav", "Pam", "Sara" };
            //Using Method Syntax
            bool ResultMS = stringArray.All(name => name.Length > 5);

            //Using Query Syntax
            bool ResultQS = (from num in stringArray
                             select num).All(name => name.Length > 5);

            Console.WriteLine("Are All Names greater than 5 Characters: " + ResultQS);
            Console.ReadKey();
        }
    }
}

Output: Are All Names greater than 5 Characters: False

Note: We need to use the All method to ensure that every element in the collection must meet the given criteria. All will return false if even one element does not satisfy the condition. It’s often used for validation checks or to ensure that a collection only contains items with certain attributes.

Example to Understand LINQ All Method with Complex Type in C#:

Let us see an example of using the LINQ All Method with Complex Data Type in C# using both Method and Query Syntax. We are going to work with the following Student and Subject classes. So, create a class file with the name Student.cs and then copy and paste the following code. As you can see, the Student class has four properties: ID, Name, TotalMarks, and Subjects. Here, within the Student class, we have also created one method, i.e., GetAllStudnets(), which will return the list of all the students. The Subject class has only two properties, i.e., SubjectName and Marks.

using System.Collections.Generic;
namespace LINQDemo
{
    public class Student
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public int TotalMarks { get; set; }
        public List<Subject> Subjects { get; set; }

        public static List<Student> GetAllStudnets()
        {
            List<Student> listStudents = new List<Student>()
            {
                new Student{ID= 101,Name = "Preety", TotalMarks = 265,
                    Subjects = new List<Subject>()
                    {
                        new Subject(){SubjectName = "Math", Marks = 80},
                        new Subject(){SubjectName = "Science", Marks = 90},
                        new Subject(){SubjectName = "English", Marks = 95}
                    }},
                new Student{ID= 102,Name = "Priyanka", TotalMarks = 278,
                    Subjects = new List<Subject>()
                    {
                        new Subject(){SubjectName = "Math", Marks = 90},
                        new Subject(){SubjectName = "Science", Marks = 95},
                        new Subject(){SubjectName = "English", Marks = 93}
                    }},
                new Student{ID= 103,Name = "James", TotalMarks = 240,
                    Subjects = new List<Subject>()
                    {
                        new Subject(){SubjectName = "Math", Marks = 70},
                        new Subject(){SubjectName = "Science", Marks = 80},
                        new Subject(){SubjectName = "English", Marks = 90}
                    }},
                new Student{ID= 104,Name = "Hina", TotalMarks = 275,
                    Subjects = new List<Subject>()
                    {
                        new Subject(){SubjectName = "Math", Marks = 90},
                        new Subject(){SubjectName = "Science", Marks = 90},
                        new Subject(){SubjectName = "English", Marks = 95}
                    }},
                new Student{ID= 105,Name = "Anurag", TotalMarks = 255,
                    Subjects = new List<Subject>()
                    {
                        new Subject(){SubjectName = "Math", Marks = 80},
                        new Subject(){SubjectName = "Science", Marks = 90},
                        new Subject(){SubjectName = "English", Marks = 85}
                    }
                },
            };

            return listStudents;
        }
    }

    public class Subject
    {
        public string SubjectName { get; set; }
        public int Marks { get; set; }
    }
}

Now, our requirement is to check whether all the students have total marks greater than 250. As you can see, the student James’s total mark is 240, less than 250. So here, the LINQ ALL method will give you the output as false. This is because the All method will return true when all the elements in the collection satisfy the given condition.

using System;
using System.Linq;
namespace LINQDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //Using Method Syntax
            bool MSResult = Student.GetAllStudnets().All(std => std.TotalMarks > 250);

            //Using Query Syntax
            bool QSResult = (from std in Student.GetAllStudnets()
                             select std).All(std => std.TotalMarks > 250);

            Console.WriteLine($"Is All Students Having Total Marks 250: {MSResult}");
            Console.ReadKey();
        }
    }
}

Output: Is All Students Having Total Marks 250: False

Complex Example to Understand LINQ All Method in C#:

Let us see a more Complex Example to Understand the LINQ All Method in C#. If you see our student’s collection, you will observe that each student object has another collection called Subjects. Now we need to fetch all the student details whose mark on each subject exceeds 80. That means we will not apply the LINQ All method to the student’s collection. Rather, we will apply the LINQ All method to the Subject collection of each student.

For a better understanding, please have a look at the following example. The Where Extension method takes a predicate as a parameter, returning a boolean true and false. Boolean TRUE means the element will return, and False means the record will not return. We are applying the LINQ All method on the Subject property within the Where Extension method. Now, for each student, the LINQ All method will execute, and it will check whether all the Subject Marks satisfied the given condition, i.e., Marks > 80, and if satisfied, the All Method will return True, and Where extension method will return that Student in output.

using System;
using System.Linq;
namespace LINQDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //Using Method Syntax
            var MSResult = Student.GetAllStudnets()
                            .Where(std => std.Subjects.All(x => x.Marks > 80)).ToList();

            //Using Query Syntax
            var QSResult = (from std in Student.GetAllStudnets()
                            where std.Subjects.All(x => x.Marks > 80)
                            select std).ToList();

            foreach (var student in QSResult)
            {
                Console.WriteLine($"{student.Name} - {student.TotalMarks}");
                foreach (var subject in student.Subjects)
                {
                    Console.WriteLine($" {subject.SubjectName} - {subject.Marks}");
                }
            }
            Console.ReadKey();
        }
    }
}

Output:

Points to Remember While Working with LINQ All Method in C#:

Here are some key points to keep in mind when using the All method:

• The All method is useful when verifying that a particular condition holds true for all elements in a sequence or collection.
• If the collection is empty (has no elements), the All method typically returns true because there are no elements that do not satisfy the condition.
• The All method is a short-circuiting operation, meaning that it stops processing and returns false when it encounters an element that doesn’t satisfy the condition.
• You can use All with other LINQ operators and predicates to perform complex checks on your data.

When To Use LINQ All Method in C#?

The All method in LINQ should be used when you need to verify that all collection elements satisfy a specific condition. Here are some scenarios where the All method is particularly useful:

• Validation: When validating a dataset, every item must meet certain criteria, such as ensuring all user-inputted data conforms to rules before processing.
• Data Integrity Checks: To ensure that data collection meets business rules or data integrity constraints, like checking all dates in a collection are within a certain range.
• Batch Operations Pre-Check: Before performing an operation that requires all items to be in a certain state, such as confirming all files are closed before starting a batch file processing operation.
• Security Authorizations: To verify that all items in a set pass a security check, such as ensuring all requests come from authenticated users.
• Conditional Execution: To decide whether to proceed with a bulk operation based on a property of all items, like checking that all products are in stock before confirming a customer’s order.

In the next article, I will discuss the LINQ Any Method in C# with Examples. In this article, I try to explain the Linq ALL Method in C# with Examples. I hope you understand the need and use of the LINQ All Method in C# with Examples.