A many to many relationship on the same table

Question

public class Product { public int Id { get; set; } public string Name{ get; set; } // lotsa other stuff public ICollection RelatedProduct{ get; set; } } Hi Let's say I have a table Product That table has a collection of 'Related Products' Ho do I configure it on the DbContext fulent api so it creates the link table? One product can be in many relatedproducts and each product can have many relatedproducts

Prasad Raveendran · Answer

To create a many-to-many relationship on the same table in SQL using Entity Framework you can follow these steps: 1. Define the model class for the table. Let's assume you have a table named Person with a primary key Id and a self-referencing foreign key FriendId that represents the many-to-many relationship. public class Person { public int Id { get; set; } public string Name { get; set; } public ICollection Friends { get; set; } public ICollection FriendOf { get; set; } } 2. Configure the many-to-many relationship in your DbContext class by overriding the OnModelCreating method. Use the Fluent API to define the relationship. public class YourDbContext : DbContext { public DbSet People { get; set; } protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity () .HasMany(p => p.Friends) .WithMany(p => p.FriendOf) .UsingEntity(j => j.ToTable(Friendship) .HasData(new { FriendsId = 1 FriendOfId = 2 } new { FriendsId = 2 FriendOfId = 3 } new { FriendsId = 3 FriendOfId = 1 })); // Example data you can customize this base.OnModelCreating(modelBuilder); } } 3. Use the Friends and FriendOf properties to navigate the many-to-many relationship. using (var context = new YourDbContext()) { var person1 = new Person { Name = Alice }; var person2 = new Person { Name = Bob }; var person3 = new Person { Name = Charlie }; person1.Friends = new List { person2 }; person2.Friends = new List { person3 }; person3.Friends = new List { person1 }; context.People.AddRange(person1 person2 person3); context.SaveChanges(); } In this example we create a many-to-many relationship between people using the Friends and FriendOf properties. We define the relationship in the OnModelCreating method using the HasMany and WithMany methods. The UsingEntity method is used to configure the intermediate table Friendship that stores the relationship data. Finally we can create and save entities to establish the many-to-many relationship.

Mudzakkir Toha · Answer

You can create tables first. and do scaffold to your project try to search scaffold on youtube or you can learn here https://www.entityframeworktutorial.net/efcore/create-model-for-existing-database-in-ef-core.aspx

Andre Silveira · Answer

@Mudzakkir Toha But how do I do it in EF core? I know how to make it in SQL server but I need it in entity framework core..

Mudzakkir Toha · Answer

There are number ways to achieve this. In Example you create product tags which is relation table between product and tag tables.