实体框架添加现有的外键

Question

我在使用 Entity Framework 建立关系以按照我希望的方式工作时遇到问题。情况如下。

一家商店有多个部门；食物、饮料、娱乐等。

有许多员工在一家商店工作。员工可以在一个或多个部门工作。

我的课程是：

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

public class Employee
{
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<EmployeeDeparmentMapping> DeparmentMappings { get; set; }
}

public class EmployeeDeparmentMapping
{
    public int Id { get; set; }
    public Employee Employee { get; set; }
    public Department Department { get; set; }

}

我首先使用代码，我的模型构建器看起来像这样

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Employee>().HasMany(e => e.DeparmentMappings).WithRequired(e => e.Employee);

        modelBuilder.Entity<EmployeeDeparmentMapping>().HasRequired(edm => edm.Department);
    }

当我尝试添加 EmployeeDeparmentMappings 时遇到问题，如下所示：

public void SomeMethod(EmployeeDeparmentMapping edm)
{
    MyDbContext myDb = new MyDbContext();
    myDb.EmployeeDepartmentMappings.Add(emd);
    myDb.SaveChanges();
}

抛出的异常是 Department 表上的 PRIMARY KEY 冲突，这是因为 EmployeeDepartmentMappings 对象中的部门可能已经存在于数据库中但不存在于 DbContext 中。

我尝试了以下方法：

public void SomeMethod(EmployeeDeparmentMapping edm)
{
    MyDbContext myDb = new MyDbContext();
    myDb.Departments.Attach(emd.Department);
    myDb.EmployeeDepartmentMappings.Add(emd);
    myDb.SaveChanges();

}

但这会引发InvalidOperationException，更改会保存到数据库，但上下文显然已损坏。

An exception of type 'System.InvalidOperationException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

Additional information: The changes to the database were committed successfully, but an error occurred while updating the object context. The ObjectContext might be in an inconsistent state. Inner exception message: A referential integrity constraint violation occurred: The property values that define the referential constraints are not consistent between principal and dependent objects in the relationship.

我在这里做错了什么？？

Answer 1

试试：

public virtual ICollection<EmployeeDeparmentMapping> DeparmentMappings { get; set; }

和

public virtual Employee Employee { get; set; }
public virtual Department Department { get; set; }

虚拟，因为它们只是用于导航目的，它们已经存在