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?

T.J. Crowder · Accepted Answer · 2020-07-15 15:15:00Z

185

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

edited Jul 15, 2020 at 15:15

T.J. Crowder

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answered Nov 30, 2016 at 21:36

Sampath

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4 Comments

RyeGuy Over a year ago

You are the man! Just ran it and got an error on the Child class as well. I am going to use this example moving forward. Thank You!

kiml42 Over a year ago

Probably worth mentioning that this is on the DBContext, rather than the Attends object, in case that's not obvious to anyone else.

prinkpan Over a year ago

Any idea why this cannot be done using annotation? Why are we forced to use fluent API?

Jonathan Wood Over a year ago

@PriyankPanchal: Because Microsoft improved things. Apparently, it worked just fine before Core.

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