ASP.NET add migration 'composite primary key error' how to use fluent API

Question

Hello I am in the process of creating a Web Application and have already installed both the Microsoft.entityFrameworkCore and Microsoft.entityFrameworkCore.Tools.

During the process of executing an add-migration in the package manager console I get an error

"System.InvalidOperationException: Entity type 'Attends' has composite primary key defined with data annotations. To set composite primary key, use fluent API"

Here is my code in the entity folder.

using System; using System.Collections.Generic; using System.ComponentModel.DataAnnotations; using System.ComponentModel.DataAnnotations.Schema; using System.Linq; using System.Threading.Tasks;  namespace _3241_farmDb.Entities {      public class Farm     {         [Required, MaxLength(30)]         [Key]         public string FarmName { get; set; }         [Required, MaxLength(15)]         public string FarmCity { get; set; }         [Required, MaxLength(9)]         public string FarmerSSN { get; set; }     }     public class Farmer     {         [Required, MaxLength(9)]         [Key]         public int SS { get; set; }         [Required, MaxLength(9)]         public string Fname { get; set; }         [Required, MaxLength(15)]         public string Lname { get; set; }         [Required, MaxLength(15)]         public string CityName { get; set; }         [Required, MaxLength(15)]         public string Address { get; set; }         [Required, MaxLength(30)]         public string BoardPositionName { get; set; }     }     public class Child     {         [Required, MaxLength(9)]         [Key]         public int FarmerSS { get; set; }         [Required, MaxLength(15)]         [Key]         public string Fname { get; set; }         [Required, MaxLength(15)]         [Key]         public string Lname { get; set; }         [Required]         public int Age { get; set; }     }     public class Attends     {          [Key, Column(Order = 1)]         public int FarmerSS { get; set; }         [Key, Column(Order = 2)]         public int HotelID { get; set; }         [Required, MaxLength(15)]         public string BoardPosition { get; set; }     }      public class Livestock     {         [Required, MaxLength(15)]         public int LivestockID { get; set; }         [Required, MaxLength(15)]         public string LivestockType { get; set; }     }     public class Farm_Houses     {         [Required, MaxLength(15)]         [Key]         public int LivestockID { get; set; }         [Required, MaxLength(15)]         public string FarmName { get; set; }     }     public class Crops     {         [Required, MaxLength(15)]         [Key]         public int CropID { get; set; }         [Required, MaxLength(15)]         public string CropName { get; set; }     } } 

How do I adjust it to set the composite key properly?

Answer 1

On EF core ..

Composite keys can only be configured using the Fluent API - conventions will never setup a composite key and you can not use Data Annotations to configure one.

Here is the Fluent API version :

Note: This is just an example. Please adjust it according to your use case.

// (In the DbContext subclass) protected override void OnModelCreating(ModelBuilder modelBuilder) {     modelBuilder.Entity<Attends>()         .HasKey(c => new { c.FarmerSS, c. HotelID }); } 

You can read more about it here : composite key