如何防止EF检索某些对象

Question

Excuse me for my broken English.

In my application, all objects in the context have a property called ObsoleteFlag, which basically means if the object should still be used on the frontend. It's some sort of "soft-delete" flag without actually having to delete the data.

Now I want to prevent EF from returning any object where ObsoleteFlag is set to true (1)

If for example I retrieve object X, the navigational list property Y contains all the related objects of type Y, no matter what the ObsoleteFlag is set to.

Is there some general way of preventing EF from doing this? I don't want to check on the ObsoleteFlag property everywhere I access the context, and for every navigational property that may be loaded too.

Thanks and sorry for my broken English.

Answer 1

Two different approaches:

1. In your repository layer have a GetAllWhatever() that returns IQueryable<Whatever> and uses Where(x => !x.Obsolete) and use this whenever you retrieve objects of this type.

2. Create a view of Create View ActiveWhatever As Select * from ActiveWhatever Where obsolete = 0 and bind to that rather than the table.

The first is essentially checking the flag every time, but doing so in one place, so you don't have to keep thinking about it.

The second is much the same, but the work is pushed to the database instead of the .NET code. If you are going to modify the entities or add new entities you will have to make it a modifiable view, but just how that is done depends on the database in question (eg you can do it with triggers in SQL Server, and triggers or rules in PostgreSQL).

The second can also include having a rule or trigger for DELETE that sets your obsolete property instead of deleting, so that a normal delete as far as Entity Framework is concerned becomes one of your soft-deletes as far as the database is concerned.

I'd go for that approach unless you had a reason to object to a view existing just to help the application's implementation (that is you're heavily into the database being "pure" in being concerned with the data rather than its use). But then, if it's handy for one application it's likely handy for more, given the very meaning of this "obsolete".