Materialize entity framework query

Question

I am using entity framework 5 for a query like this:

var query = 
    from i in context.Instrument
    from p in i.InstrumentPerformance  // 1 : n
    where          


        

Answer 1

It is possible to retrieve the objects in one take first and then create the dictionaries by:

var query = 
    (from i in context.Instrument
    select new { 
                 i,
                 ps = i.InstrumentPerformance
                          .Where(p.PortfolioScenarioID == 6013)
               }).AsEnumerable()
               .Select(x => x.i);

This materializes and selects Instrument entities and, here's the trick, their partly loaded InstrumentPerformance collections. I.e. the instruments only contain InstrumentPerformance entities that meet the condition PortfolioScenarioID == 6013. This is because EF runs a process known as relationship fixup that ties child objects to the right parent object when they are fetched from the database.

So now you can dispose the context and any time after that do

var perf = query.First(i => i.InstrumentID == 407240).InstrumentPerformance;

or build your dictionaries using from i in query in stead of from i in context.Instrument.

IMPORTANT: lazy loading should be disabled, otherwise EF will still try to load the full collections when they are addressed.