实体框架DbContext更新值，无需查询且通过外键 [英] Entity framework DbContext update value without query and by foreign key

问题描述

我有一种更新某些表的方法。要进行更新，我需要先获取 TestProcess ，但我不喜欢这样。如何在没有 select（firstOrDefault）操作的情况下更新 TestProcess ，该操作仅用于更新操作？

I have a method for updating some tables. For update I need get first of TestProcess, but I don't like that. How can I update TestProcess without select(firstOrDefault) operation, used only for the update operation?

方法示例：

public void UpdateTestProcess(int id, string updateID)
{
    using (TestEntities context = new TestEntities())
                {
                    TestProcess pr = context.TestProcess.FirstOrDefault(x => x.MyID == id);
                    pr.UpdateID = updateID;             

                    context.TestProcess.Attach(pr);
                    context.ObjectStateManager.ChangeObjectState(pr, EntityState.Modified);
                    context.SaveChanges();
               }
}

推荐答案

TestProcess pr = new TestProcess()
{
    MyID == id,
};

context.Set<TestProcess>().Attach(pr);

pr.UpdateID = updateID;

context.SaveChanges();

如果将值设置为该类型的默认值（例如，设置 int 到 0 ），则不会将其作为更改，而您需要手动设置状态。

If you are setting the value to the default value of that type (for example, setting an int to 0) it won't be picked up as a change, and you need to manually set the state.

pr.UpdateID = updateID;
context.Entry(pr).Property(p => p.UpdateID).IsModified = true;

您可以将此类代码放在扩展方法中，这样您就可以执行以下操作（将实现保留为练习）：

You can put such code away in extension methods, so you can do things like this (I'll leave the implementation as an exercise):

Foo entity = this.DbContext.GetEntityForUpdate<Foo>(
    item => item.ID, model.ID
    );

this.DbContext.UpdateProperty(entity, item => item.Name, model.Name);

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