无法在对象'dbo.User'中插入重复键。\ r \ n声明已终止

Question

我有一个用户表。从其他表中可以看到此表格对像CreatedBy这样的字段的引用。

问题是，当我插入另一个表的行（例如'x'）时，它会尝试将新用户插入到用户表中。

它应该做的是在CreatedBy作为现有用户的表'x'中插入一行。

使用Entity Framework 4.任何人都遇到过这样的问题吗？

Answer 1

您可以将实体与相关实体一起插入，也可以插入实体而不引用相关实体，只需引用现有实体即可。这取决于你编写的代码。

实施例1：

User user = GetUserFromSomewhere(); 
using (var context = new MyContext()) 
{ 
    Order order = new Order(); 
    order.CreatedBy = user; 

    context.Orders.AddObject(order); 
    // will put both order and related entity user into Added state 
    // because user is not attached to the context 

    context.SaveChanges(); 
    // creates new order and new user and sets the relationship between them 
} 

实施例2：

using (var context = new MyContext()) 
{ 
    User user = context.Users.SingleOrDefault(u => u.Id == 1); 
    // query attaches this user to this context 
    // user is in state Unchanged now 

    Order order = new Order(); 
    order.CreatedBy = user; 

    context.Orders.AddObject(order); 
    // will put the order into Added state but doesn't touch the 
    // state of already attached related entities -> user remains 
    // in state Unchanged 

    context.SaveChanges(); 
    // creates new order with reference to user, but doesn't create new user 
} 

实施例3：

User user = GetUserFromSomewhere(); 
using (var context = new MyContext()) 
{ 
    context.Users.Attach(user); 
    // we attach explicitely to the context telling EF thereby 
    // that we know that this user exists in the DB 
    // user is in state Unchanged now 

    Order order = new Order(); 
    order.CreatedBy = user; 

    context.Orders.AddObject(order); 
    // will put the order into Added state but doesn't touch the 
    // state of already attached related entities -> user remains 
    // in state Unchanged 

    context.SaveChanges(); 
    // creates new order with reference to user, but doesn't create new user 
} 

编辑

实施例4：

int userId = GetUserIdFromSomewhere(); 
using (var context = new MyContext()) 
{ 
    var user = new User { Id = userId }; 
    // we create a stub user entity with the correct primary key 
    // It's not necessary to set other properties 
    // to only set the relationship to the order 

    context.Users.Attach(user); 
    // we attach explicitely to the context telling EF thereby 
    // that we know that this user exists in the DB 
    // user is in state Unchanged now 

    Order order = new Order(); 
    order.CreatedBy = user; 

    context.Orders.AddObject(order); 
    // will put the order into Added state but doesn't touch the 
    // state of already attached related entities -> user remains 
    // in state Unchanged 

    context.SaveChanges(); 
    // creates new order with reference to user, but doesn't create new user 
}