How to add foreign key using fluent API when only model1 has reference to other model?

Question

how can I add a foreign key using fluent api?

eg.

model1

id, name, model2.id

model2

id, name

I've read about HasOne Method for building one to one relationship but this example shows the model1 only have reference to model2.

Answer 1

I create a demo below which model1 is Employee and model2 is Department, Employee has a reference to Department

models:

public class Employee
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }

    public int DepartmentId { get; set; }
    public Department Department { get; set; }
}

public class Department
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }

}

dcContext:

protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        builder.Entity<Employee>()
        .HasOne(e => e.Department)
        .WithOne()
        .HasForeignKey<Employee>(e => e.DepartmentId);

    }

result:

migrationBuilder.CreateTable(
            name: "Employees",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false)
                    .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                Name = table.Column<string>(nullable: true),
                DepartmentId = table.Column<int>(nullable: false)
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Employees", x => x.Id);
                table.ForeignKey(
                    name: "FK_Employees_Department_DepartmentId",
                    column: x => x.DepartmentId,
                    principalTable: "Department",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.Cascade);
            })