Entity Framework Multiple Column as Primary Key by Fluent Api

Question

These are my simplified domain classes.

public class ProductCategory {     public int ProductId { get; set; }     public int CategoryId { get; set; }      public virtual Product Product { get; set; }     public virtual Category Category { get; set; } }  public class Product {     public int Id { get; set; }     public string Name { get; set; } }   public class Category {     public int Id { get; set; }     public string Name { get; set; }     public int? ParentCategoryId { get; set;}  }  

This is my mapping class. But it doesn't work.

public class ProductCategoryMap : EntityTypeConfiguration<ProductCategory> {     public ProductCategoryMap()     {         ToTable("ProductCategory");         HasKey(pc => pc.ProductId);         HasKey(pc => pc.CategoryId);     } } 

How should I map these classes to provide, so that one product can be seen in multiple categories?

Answer 1

Use anonymous type object instead of 2 separated statements:

HasKey(pc => new { pc.ProductId, pc.CategoryId }); 

From Microsoft Docs: EntityTypeConfiguration.HasKey Method

If the primary key is made up of multiple properties then specify an anonymous type including the properties. For example, in C# t => new { t.Id1, t.Id2 } and in Visual Basic .Net Function(t) New With { t.Id1, t.Id2 }.