無法在對象'dbo.User'中插入重複鍵。\ r \ n聲明已終止

Question

我有一個用戶表。從其他表中可以看到此表格對像CreatedBy這樣的字段的引用。

問題是，當我插入另一個表的行（例如'x'）時，它會嘗試將新用戶插入到用戶表中。

它應該做的是在CreatedBy作爲現有用戶的表'x'中插入一行。

使用Entity Framework 4.任何人都遇到過這樣的問題嗎？

Answer 1

您可以將實體與相關實體一起插入，也可以插入實體而不引用相關實體，只需引用現有實體即可。這取決於你編寫的代碼。

實施例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 
} 

實施例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 
} 

實施例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 
} 

編輯

實施例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 
}