Question

据我所知，EntityCollection.Attach和EntityReference.Attach只能创建数据库中已存在的关系。换句话说，如果Address.EmployeeID == Employee.EmployeeID，则以下代码将起作用：

        Employee employee = context.Employees.First();
        Address address = context.Addresses.First();
        employee.Addresses.Attach(address);

但是如果Address.EmployeeID != Employee.EmployeeID，则代码将抛出异常：

        Employee employee = context.Employees.First();
        Address address = context.Addresses.First();
        employee.Addresses.Attach(address); // System.InvalidOperationException: A 
                                            // referential integrity constraint
                                            // violation occurred

但根据以下thread中的代码示例，EntityCollection.Attach和EntityReference.Attach也可用于创建DB中不存在的关系：

var existingPerson = ctx.Persons.SingleOrDefault(p => p.Name = "Joe Bloggs" };
var myAddress = ctx.Addresses.First(a => a.PersonID != existingPerson.PersonID);
existingPerson.Addresses.Attach(myAddress);
// OR:
myAddress.PersonReference.Attach(existingPerson)
ctx.SaveChanges();

因此，我假设EntityCollection.Attach和EntityReference.Attach只能创建数据库中已存在的关系，并且从其他线程获取的代码示例应该抛出异常，我是否正确？

谢谢

Answer 1

是的，我认为这只是一个输入错误，或者作者写了一些不完整的内容。

var existingPerson = ctx.Persons.SingleOrDefault(p => p.Name = "Joe Bloggs" };
var myAddress = ctx.Addresses.First(a => a.PersonID == existingPerson.PersonID);
existingPerson.Addresses.Attach(myAddress);
// OR:
myAddress.PersonReference.Attach(existingPerson)
ctx.SaveChanges();

实体框架：不应该附加以下实体抛出异常？

1 个答案: