EF 4.0 自跟踪实体，预期更新正在转换为插入

发布于 2024-10-31 19:01:30 字数 615 浏览 1 评论 0原文

我们假设以下方法位于 WCF 服务中。 UI 检索 Status 对象的实例，并使用此方法对服务进行后续调用。它没有像我预期的那样将状态分配给用户，而是尝试插入状态。我做错了什么？

void Method(Status status)
{
    //not sure if this is even needed, the status never changed
    context.Statuses.ApplyChanges(status);

    //get the first user from the database
    User user = context.Users.Where(u => u.Id = 1).First();

    //set user status to some existing status
    user.Status = status;

    //this throws an exception due to EF trying to insert a new entry
    //into the status table, rather than updating the user.StatusId column.
    context.SaveChanges();
}

原文

Let's assume that the below method lives in a WCF service. The UI retrieved an instance of the Status object, and makes a subsequent call to the service using this method. Instead of assigning the status to the user as I would expect, it attempts to insert the status. What am I doing wrong?

void Method(Status status)
{
    //not sure if this is even needed, the status never changed
    context.Statuses.ApplyChanges(status);

    //get the first user from the database
    User user = context.Users.Where(u => u.Id = 1).First();

    //set user status to some existing status
    user.Status = status;

    //this throws an exception due to EF trying to insert a new entry
    //into the status table, rather than updating the user.StatusId column.
    context.SaveChanges();
}

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许仙没带伞 2024-11-07 19:01:30

问题是您正在与附加用户一起工作。当 STE 附加到上下文时，它的行为方式与任何其他实体完全相同。而且它的自我跟踪机制没有被激活。因此，在将状态设置给用户之前，您必须将状态附加到上下文，否则它将被作为必须插入的新实体进行跟踪：

void Method(Status status)
{
    User user = context.Users.Where(u => u.Id = 1).First();

    context.Attach(status);
    user.Status = status;

    context.SaveChanges();
}

The problem is that you are working with attached user. When the STE is attached to the context it behaves exactly in the same way as any other entity. More over its self tracking mechanism is not activated. So you must attach the status to the context before you set it to the user or it will be tracked as a new entity which has to be inserted:

void Method(Status status)
{
    User user = context.Users.Where(u => u.Id = 1).First();

    context.Attach(status);
    user.Status = status;

    context.SaveChanges();
}

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能怎样 2024-11-07 19:01:30

试试这个：

        using (Entities ctx = new Entities())
        {
            ctx.Statuses.Attach(status);

            ObjectStateEntry entry = ctx.ObjectStateManager.GetObjectStateEntry(status);
            entry.ChangeState(EntityState.Modified);

            //get the first user from the database
            User user = ctx.Users.Where(u => u.Id = 1);

            //set user status to some existing status
            user.StatusID = status.StatusID;

            ctx.SaveChanges();
        }

这是关于使用实体框架进行 CRUD 的教程如果你有兴趣的话。

Try this instead:

        using (Entities ctx = new Entities())
        {
            ctx.Statuses.Attach(status);

            ObjectStateEntry entry = ctx.ObjectStateManager.GetObjectStateEntry(status);
            entry.ChangeState(EntityState.Modified);

            //get the first user from the database
            User user = ctx.Users.Where(u => u.Id = 1);

            //set user status to some existing status
            user.StatusID = status.StatusID;

            ctx.SaveChanges();
        }

Here's a tutorial on CRUD with Entity Framework if you're interested.

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