Left Join

Jasurbek Xasanboyev

Avvalgi JOIN tularidan farqli tomoni LEFT JOIN da maydon bo’sh bo’lishi ham mumkin. Ikki ro’yhatni birlashtirish vaqtida agar to’g’ri keladigan maydon topilmasa uni bo’sh holatda (null) tashlab ketadi. Buning uchun DefaultEmpty metodidan foydalanamiz:

Query Syntax:

class Program
{
    static void Main(string[] args)
    {
        var students = new List<Student>()
    {
        new Student() { Id = 1, Name = "Jasurbek", AddressId = 1},
        new Student() { Id = 2, Name = "Xondamir", AddressId = 5},
        new Student() { Id = 3, Name = "Shoxruh", AddressId = 3},
        new Student() { Id = 4, Name = "Shaxzod", AddressId = 4},
        new Student() { Id = 5, Name = "Abdulloh"}
    };
        var addresses = new List<Address>()
    {
        new Address() {Id = 1, AddressLine = "Line 1"},
        new Address() {Id = 2, AddressLine = "Line 2"},
        new Address() {Id = 3, AddressLine = "Line 3"},
        new Address() {Id = 4, AddressLine = "Line 4"},
    };
        var QueerySyntax = from std in students
                            join add in addresses on
                            std.AddressId equals add.Id into
                            stdAddress
                            from studentAddress in stdAddress.DefaultIfEmpty()
                            select new { Name = std.Name, StudentAddress = studentAddress != null ? studentAddress.AddressLine : "Empty"};
        foreach (var item in QueerySyntax)
        {

            Console.WriteLine($"Name: {item.Name} Line: {item.StudentAddress}");
        }
        /*OUTPUT:   Name: Jasurbek Line: Line 1
                    Name: Xondamir Line: Empty
                    Name: Shoxruh Line: Line 3
                    Name: Shaxzod Line: Line 4
                    Name: Abdulloh Line: Empty  */
    }
}
class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int AddressId { get; set; }
}
class Address
{
    public int Id { get; set; }
    public string AddressLine { get; set; }
}

Method Syntax:

class Program
{
    static void Main(string[] args)
    {
        var students = new List<Student>()
    {
        new Student() { Id = 1, Name = "Jasurbek", AddressId = 1},
        new Student() { Id = 2, Name = "Xondamir", AddressId = 5},
        new Student() { Id = 3, Name = "Shoxruh", AddressId = 3},
        new Student() { Id = 4, Name = "Shaxzod", AddressId = 4},
        new Student() { Id = 5, Name = "Abdulloh"}
    };
        var addresses = new List<Address>()
    {
        new Address() {Id = 1, AddressLine = "Line 1"},
        new Address() {Id = 2, AddressLine = "Line 2"},
        new Address() {Id = 3, AddressLine = "Line 3"},
        new Address() {Id = 4, AddressLine = "Line 4"},
    };
            var MethodSyntax = students.GroupJoin(addresses, std => std.AddressId, add => add.Id,
                (std, add) => new { std, add }).SelectMany(x => x.add.DefaultIfEmpty(), 
                (StudentData, AddressData) => new { Name = StudentData.std.Name, Line = AddressData != null ? AddressData.AddressLine : "Empty"});
        foreach (var item in MethodSyntax)
        {

            Console.WriteLine($"Name: {item.Name} Line: {item.Line}");
        }
        /*OUTPUT:   Name: Jasurbek Line: Line 1
                    Name: Xondamir Line: Empty
                    Name: Shoxruh Line: Line 3
                    Name: Shaxzod Line: Line 4
                    Name: Abdulloh Line: Empty  */
    }
}
class Student
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int AddressId { get; set; }
}
class Address
{
    public int Id { get; set; }
    public string AddressLine { get; set; }
}