C# ASP.NET - Add Foreign Key In Entity Framework

How to add relationship in EFCore

• For example, if we have the two classes as below.

// VillaNumber.cs
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace MagicVilla_VillaAPI.Models
{
    public class VillaNumber
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int VillaNo { get; set; }
        public string SpecialDetails { get; set; }
        public DateTime CreatedDate { get; set; }
        public DateTime UpdatedDate { get; set; }
    }
}

// Villa.cs
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace MagicVilla_VillaAPI.Models
{
    public class Villa
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }
        public string Name { get; set; }
        public string Details { get; set; }
        public double Rate { get; set; }
        public int Sqft { get; set; }
        public int Occupancy { get; set; }
        public string ImageUrl { get; set; }
        public string Amenity { get; set; }
        public DateTime CreatedDate { get; set; }
        public DateTime UpdatedDate { get; set; }
    }
}

• To add 1-to-many relationship for Villa and VillaNumber. Basically, we need to create a navigation property. We do the followings.

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace MagicVilla_VillaAPI.Models
{
    public class VillaNumber
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int VillaNo { get; set; }
        #region Add relationship
        [ForeignKey("Villa")]
        public int VillaId { get; set; }
        public Villa Villa { get; set; }
        #endregion
        public string SpecialDetails { get; set; }
        public DateTime CreatedDate { get; set; }
        public DateTime UpdatedDate { get; set; }
    }
}

• Then, we need to run the migration to update the database.

PM> add-migration AddFKToVillaTable

As a result, EFCore generates a migration snapshot file and if we take a closer look into this file, we will see that the foreign key is added.

migrationBuilder.CreateIndex(
    name: "IX_VillaNumbers_VillaId",
    table: "VillaNumbers",
    column: "VillaId");

migrationBuilder.AddForeignKey(
    name: "FK_VillaNumbers_Villas_VillaId",
    table: "VillaNumbers",
    column: "VillaId",
    principalTable: "Villas",
    principalColumn: "Id",
    onDelete: ReferentialAction.Cascade);

Note:

• principleTable: Villa table
• principleColumn: the Id in the Villa table
• onDelete: ReferentialAction.Cascade: if the row on Villa is deleted, the related row of table VillaNumber is also deleted.

Last and not least, we need to run PM> update-database to update database so that the changes can take the effect.