Question

我正在使用EF代码第一种方法，并希望添加一个链接（地图）表。我正在处理以下示例并得到以下错误：

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

问题是我不想在这张桌子上放一把钥匙，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;
}

我尝试了各种各样的事情，例如添加“[Key（）]”属性，但是它没有意义，我将它添加到哪个字段？我想知道是否支持这种表模型？

Answer 1

您正在尝试制作“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DbContext：

中

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");
                });
    }
}

Answer 2

对于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;

}

有关详细信息，请查看Create code first, many to many

我希望这会对你有所帮助。

实体框架代码第一张地图（链接）表？

2 个答案: