EF1: Filtering derived types of entity class using .OfType<> by passing a string value

Question

I have a situation where I'm trying to filter a LINQ select using a derived sub class.

ctx.BaseEntity.OfType<SubClass>() - this works fine.

However I'd like to do this using a string value instead. I've come across a performance barrier when I have lots (>20) Sub Classes and selecting an Entity without using OfType just isn't an option. I have a generic UI that renders from the base class, so I don't know what Class Type will be returned at compile time.

So what I'd like to do is this:

1. Perform a projected Select where I return just the SubClassType from the database

2. Perform a second select using this value as the OfType to only select the relevant related entity from the database (No mass unions generated)

       int id = 1;
       var classType = (from c in ctx.BaseClass.Include("ClassType")
                                  where c.id == id
                                  select new
                                             {
                                                 c.ClassType.TypeName
                                             }).First();
   
       BaseClass caseQuery = ctx.BaseClass.OfType<classType.TypeName>()
                       .Include("ClassType")
                       .Include("ChildEntity1")
                       .Include("ChildEntity2")
                       .Where(x => x.id== id);
   

But obviously this won't work because OfType requires a Type and not a string.

Any ideas on how I can achieve this?

Update: As a side note to the original question, it turns out that the moment you project a query that uses a Navigation Property - it builds the monster SQL too, so I've ended up using a stored procedure to populate my ClassType entity from the BaseClass Id.

Answer 1

So I've just got it to work using eSQL, which I'd never used before. I've posted the code here just in case it helps someone. Has anyone else got a more strongly typed solution they can think of?

BaseClass caseQuery = ctx.BaseClass.CreateQuery<BaseClass>("SELECT VALUE c FROM OFTYPE(Entities.[BaseClass],namespace.[" + classType.TypeName + "])  as c")
                .Include("ClassType")
                .Include("ChildEntity1")
                .Include("ChildEntity2")
                .Where(x => x.id== id).FirstOrDefault();