Multiple Include and Where Clauses Linq

Question

I have a database where I'm wanting to return a list of Clients.

These clients have a list of FamilyNames.

I started with this

var query = DbContext.Clients.Include(c => c.FamilyNames).ToList() //returns all clients, including their FamilyNames...Great.

But I want somebody to be able to search for a FamilyName, ifany results are returned, then show the clients to the user.

so I did this...

var query = DbContext.Clients.Include(c => c.FamilyNames.Where(fn => fn.familyName == textEnteredByUser)).ToList();

I tried...

var query = DbContext.Clients.Include(c => c.FamilyNames.Any(fn => fn.familyName == textEnteredByUser)).ToList();

and...

var query = DbContext.FamilyNames.Include(c => c.Clients).where(fn => fn.familyname == textEnteredByUser.Select(c => c.Clients)).ToList();

What I would like to know (obviously!) is how I could get this to work, but I would like it if at all possible to be done in one query to the database. Even if somebody can point me in the correct direction.

Kind regards

Answer 1

In Linq to Entities you can navigate on properties and they will be transformed to join statements.

This will return a list of clients.

var query = DbContext.Clients.Where(c => c.FamilyNames.Any(fn => fn == textEnteredByUser)).ToList();

If you want to include all their family names with eager loading, this should work:

var query = DbContext.Clients.Where(c => c.FamilyNames.Any(fn => fn == textEnteredByUser)).Include(c => c.FamilyNames).ToList();

Here is some reference about loading related entities if something doesn't work as expected.

Answer 2

You can use 'Projection', basically you select just the fields you want from any level into a new object, possibly anonymous.

var query = DbContext.Clients
    .Where(c => c.FamilyNames.Any(fn => fn == textEnteredByUser))
    // only calls that can be converted to SQL safely here
    .Select(c => new {
        ClientName = c.Name,
        FamilyNames = c.FamilyNames
    })
    // force the query to be materialized so we can safely do other transforms
    .ToList()
    // convert the anon class to what we need
    .Select(anon => new ClientViewModel() {
        ClientName = anon.ClientName,
        // convert IEnumerable<string> to List<string>
        FamilyNames = anon.FamilyNames.ToList()
    });

That creates an anonymous class with just those two properties, then forces the query to run, then performs a 2nd projection into a ViewModel class.

Usually I would be selecting into a ViewModel for passing to the UI, limiting it to just the bare minimum number of fields that the UI needs. Your needs may vary.