EF6.1如何在处理大量对象时从父实体快速删除子实体

Question

I've tried searching for this but I fear my criteria isn't correct, I've used examples given but I've still ended up at this point.

I'm experimenting with EF6.1 and I have a data set consisting of a parent that is linked to a child. its zero or one to many, and maybe that's my problem.

so parent has a table called childID, and a relationship called child.

when I set childID on the parent, EF automatically gets the child object as parent.child and its all good. if I change the childID, then its mapped to the new child and its all good.

I can bulk update say, 10,000 parents with a new childID and its all fast and good.

the issue is this, I need to be able to remove the childID so its back to NULL, thus removing the link to the child from the parent. the child still exists. tens of thousands of parents may link to this child.

so far searching here looks like I in fact have to get child.parents.remove(parent); and this is where i'm hitting a severe performance issue. EF seems to lookup every parent that the child has, giving the database some 10,000 record hit, then it removes the correct one. but if I want to remove say 9,000 or all 10,000, then since I can only remove one at a time it does 10,000 loops of a 10,000, 9,999, 9,998... sql select, just to then removes one item at a time on each loop, this is extremely slow and the test application just sits there eating cpu time. an operation such as this takes around 10 minutes.

I had originally thought I could just set parent.childID = null but that does nothing.

am I doing something wrong? is EF just not up to the task? is another ORM up to the task? maybe this isn't a job for an ORM anyway?

first post here so please go easy on me :)

Answer 1

I just asked this same question not long ago. While EF is nice, sometimes it's not possible to use it when dealing with a huge amount of data. The solution we came up with involved writing SQL stored procedures and executing those in place of our deletion using EF.

Answer 2

okay so the stored procedure was the way to go, very simple in the end.

create a stored procedure in sql for example 'RemoveChild' and it takes one bigint input parameter called @ParentID

which does an UPDATE parents SET ChildID = null WHERE ParentID = @ParentID

import that in EF using the model diagram page thing and it created a new public function called dbcontext.RemoveChild(long ParentID). call that in code and the magic happens instantly. I called it inside a using dbcontext and did a .saveChanges() afterward, not sure if that's needed but that structure was already in place.

note that this particular stored procedure is specific to that entity and not generic, might be a way to do it generically, I haven't looked yet.

why EF cant do this I have no idea.