Linq left join with Entity Framework

Question

I have a table of Vehicles and I need to do a left join on VehicleAttribute.

var vehicle = (from v in context.Vehicles
                               //join vehicleAttributes
                               join va in context.VehicleAttributes on v.VehicleId equals va.VehicleId into vAttributes
                               from vehicleAttributes in vAttributes.DefaultIfEmpty()

                               where v.VehicleId == vehicleId
                               select new { v, vehicleAttributes });

so far so good. VehicleAttribute has also a column AttributeId. And I only need to join those VehicleAttributes when it's in this List:

List<Guid> allowedAttributes = (from ua in context.UserAttributes
                                                    where ua.UserId == UserSession.CurrentUser.UserId
                                                    select ua.AttributeId).ToList();

How would I do that? I think a subquery might be the right approach but I'm struggling..

Thanks for all answers.

EDIT: A different approach to explain my problem: I have these two queries

SELECT Vehicle.VehicleId,VehicleAttribute.AttributeId
FROM Vehicle
LEFT JOIN VehicleAttribute
ON Vehicle.VehicleId = VehicleAttribute.VehicleId

SELECT UserAttribute.AttributeId
FROM UserAttribute
WHERE UserAttribute.UserId = '4D0F8AD2-7A4D-4E29-A6D3-E5FCD6075388'

and want to combine them so I only get the attribute id's which are in the second query. A where clause doesn't work because I still want the vehicleId even if there are no attributeIds

Answer 1

Not sure this is your scenario. You could try to Left join with a subquery:

//define the query that returns allowed VehicleAttributes
allowedAttributesQuery =from ua in context.UserAttributes
                          where ua.UserId == UserSession.CurrentUser.UserId
                          select ua.VehicleAttribute;  //I suppose that VehicleAttribute navigation property exists in the UserAttribute 

//query that joins Vehicles with the allowedAttributes subquery
var vehicle = (from v in context.Vehicles
                           join va in allowedAttributesQuery on v.VehicleId equals va.VehicleId into vAttributes
                           from vehicleAttributes in vAttributes.DefaultIfEmpty()

                           where v.VehicleId == vehicleId
                           select new { v, vehicleAttributes });

Answer 2

After you defined allowedAttributes you can change

vAttributes.DefaultIfEmpty()

of your first query to:

vAttributes
    .Where(va => allowedAttributes.Contains(va.AttributeId))
    .DefaultIfEmpty()