Question

I have a linq query

Context.Set<Entity>().where(x=>x.condition == true).select(x=> new ViewModel{Property = x.Property});

I would like to be able to make a change to the linq query through something like this

Context.Set<Entity>().ChangeLinqQuery("String").where(x=>x.condition == true).select(x=> new ViewModel{Property = x.Property});

So that when I capture the DbCommandTree in my EFProviderWrapper I will be able to spot the change and capture the String. I also wish to be sure that the expression is applied to that particular reference to the Entity so that if I join the Entity on itself it will still be able to tell that that particular reference to Entity is the one I mean to alter.

The goal is to be able to alter the SQL generated by EF, so if you have a better means of achieving this goal please feel free to provide it.

Answer 1

I don’t think this is possible. Your ChangeLinqQuery will have to add some custom expression into expression tree created on behind. The problem is that this expression tree is translated to ESQL – that is what DbCommandTree describes (it is not SQL). As I know ESQL is not extensible and so you cannot add any custom expressions to this process. Even if you could it would also most probably mean that you will have to rewrite much of SQL generation to satisfy your needs = not developing provider wrapper but provider itself.

Your best choice with EF is simply replace table names in generated SQL which will be complex, slow and unless you build strong SQL parser following its syntax it will also be error prone.

Your best choice is simply not using EF as I already recommended in your previous question.