如何通过实体框架中的导航属性更新实体？ [英] How to update entity through navigation properties in entity framework?

问题描述

我有TableA（ID，Name和TableB_ID）和TableB（TableB_ID，Description），它们有1对多的关系。

创建一个上下文，我想更新TableA中的记录，更改其TableB_ID值。

事情是：我不想直接更新tableB_ID的值。我想通过从TableB中指定不同的描述值来更改该记录。



我是否必须写这个或实体框架是否为我做这个？



谢谢



我尝试过：



使用TableA的导航属性更改描述的值不起作用。

Hi,
I have TableA(ID,Name and TableB_ID) and TableB(TableB_ID,Description), which have a 1 to many relationship.
After creating a context, I want to update a record in TableA, changing its TableB_ID value.
The thing is: I don't want to update the value of tableB_ID directly. I want to change that record by specifying a different "Description" value from TableB.

Do I have to write this or does entity framework do this for me?

THanks

What I have tried:

Changing the value of "Description" by using the navigation properties of TableA is not working.

推荐答案

我认为描述是唯一的。因此，您必须自己搜索匹配的描述。它是这样的：

I assume that description is unique. So you'll have to search for a matching description yourself. It is something like this:

var descr = "something";
var tabB = context.TableB.FirstOrDefault(f => f.Description == descr );

if (tabB == null)
{
    // Assume TableB_ID is autonumber / identity in database.
    var newTabB = new TableB() { Description = descr };
    TableA.TableB = newTabB ;
    // Not sure if this line is required.
    context.TableB.Add(newTabB);
}
else
    TableA.TableB = tabB;

context.SaveChanges();

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