4

我正在使用 EF 代码优先方法，并希望添加一个链接（地图）表。我正在处理以下示例并收到以下错误：

System.Data.Entity.Edm.EdmEntityType: : EntityType 'EmployeeDepartmentLink' has no key defined. Define the key for this EntityType.

问题是我不想要这张桌子上的钥匙，它只是将两张桌子映射在一起：

public class Employee
{
    [Key()]
    public int EmployeeID;
    public string Name;
}

public class Department
{
    [Key()]
    public int DepartmentID;
    public string Name;
}

public class EmployeeDepartmentLink
{
    public int EmployeeID;
    public int DepartmentID;
}

我尝试了各种方法，例如添加“[Key()]”属性，但使用它没有意义，我应该将它添加到哪个字段？我想知道是否甚至支持这种表模型？

4

2 回答 2

15

您正在尝试进行“多对多”映射。

要执行此操作，请编写以下代码：

public class Employee
{
    [Key]
    public int EmployeeId;
    public string Name;
    public List<Department> Departments { get; set; }

    public Employee()
    {
        this.Departments = new List<Department>();
    }
}

public class Department
{
    [Key]
    public int DepartmentId;
    public string Name;

    public List<Employee> Employees { get; set; }

    public Department()
    {
        this.Employees = new List<Employee>();
    }
}

然后，在你的DbContext：

public class YourContext : DbContext
{
    public DbSet<Employee> Employees { get; set; }
    public DbSet<Department> Departments { get; set; }

    public YourContext() : base("MyDb")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Department>().
            HasMany(c => c.Employees).
            WithMany(p => p.Departments).
            Map(
                m =>
                {
                    m.MapLeftKey("DepartmentId");
                    m.MapRightKey("EmployeeId");
                    m.ToTable("DepartmentEmployees");
                });
    }
}
于 2013-01-21T15:34:10.977 回答
2

因为M:M relationship您必须创建您的加入（链接）类，如下所示。

public class EmployeeDepartmentLink
{
    [Key, Column(Order = 0)]
    public int EmployeeID;

    [Key, Column(Order = 1)]
    public int DepartmentID;

}

有关更多信息，请查看先创建代码，多对多

我希望这对你有帮助。

于 2013-01-21T14:50:36.627 回答