Question

This is my real world example.
I have 4 tables:

• Person
• Plan
• Coverage
• CoveredMembers

Each person can have many plans, each of those plans can have many coverages. Each of those coverages can have many CoveredMembers.

I need a query that will apply a filter on Plan.PlanType == 1 and CoveredMembers.TermDate == null.
This query should bring back any person who has a medical type plan that is not terminated.

This SQL statement would do just that:

SELECT Person.*, Plans.*, Coverages.*, CoveredMembers.* 
FROM Person P 
INNER JOIN Plan PL ON P.PersonID = PL.PersonID 
INNER JOIN Coverage C on PL.PlanID = C.PlanID 
INNER JOIN CoveredMember CM on C.CoverageID = CM.CoverageID 
WHERE CM.TermDate = NULL AND PL.PlanType = 1

I have figured out how to do this using anonymous types, but I sometimes need to update the data and save back to the database – and anonymous types are read only.

I was given a solution that did work using JOIN but it only brought back the persons (albeit filtered the way I needed). I can then loop through each person:

foreach (var person in persons) {
  foreach (var plan in person.Plans{
    //do stuff 
  }
}

But wouldn’t that make a db call for each iteration of the loop? I have 500 persons with 3 unterminated medical plans each, so it would call the db 1500 times?

This is why I want to bring the whole data tree from Persons to CoveredMembers back in one shot. Is this not possible?

Answer 1

I believe this is accomplished in two parts:

1. Your query to determine the people you wish to have returned based on your criteria as discussed in this question previously: Entity framework. Need help filtering results

2. Properly setting the navigation properties for entities you want brought together to be eagerly loaded: http://msdn.microsoft.com/en-us/data/jj574232.aspx

For example if your Person entity looks like:

public class Person {
   public List<Plan> Plans {get; set;}
   ...
}

When returning data from the dbcontext you can also use explicit eager loading with the include option:

 var people = context.People
         .Include(p => p.Plans)
         .ToList();
....

If these are nested – coverage is part of plan, etc (which it looks like, it goes something like):

 var people = context.People
         .Include(p => p.Plans.Select(pl=>pl.Coverage).Select(c=>c.CoveredMembers)))
         .ToList();
....

I am making some assumptions about your data model here, and my code above probably needs a little tweaking.

EDIT:

I might need someone else to weigh in here, but I don’t think you can add the where clause into an include like that (my example above leads you that way a bit by putting the include on the context object, instead return an IQueryable with your conditions set as solved in your first post (without a ToList() called on it) and then use the code you wrote above without the Where clauses:

From first post (you supplied different criteria in this one, but same concept)

 var q = from q1 in dbContext.Parent
    join q2 in dbContext.Children
    on q1.key equals q2.fkey
    join q3 in  ........
    where q4.col1 == 3000
    select q1;

Then:

List<Person> people = q.Include(p => p.Plans
  .Select(pl => pl.Coverages)
  .Select(c => c.CoveredMembers).ToList();

Again, doing this without being able to troubleshoot – I am sure it would take me a few attempts to iron this one out too.