Question

To explain my problem more easily I will create the following fictional example, illustrating a very basic many-to-many relationship. A Car can have many Parts, and a Part can belong to many Cars.

DB SCHEMA:

CAR_TABLE
---------
CarId
ModelName

CAR_PARTS_TABLE
---------------
CarId
PartId

PARTS_TABLE
-----------
PartId
PartName

CLASSES:

public class Car 
{
  public int CarId {get;set;}
  public string Name {get;set;}
  public IEnumerable<Part> Parts {get;set;}
}

public class Part 
{
  public int PartId {get;set;}
  public string Name {get;set}
}

Using this very simple model I would like to get any cars that have all the parts assigned to them from a list of parts I am searching on.

So say I have an array of PartIds:

var partIds = new [] { 1, 3, 10};

I want to mimic the following c# code in terms of a database call:

var allCars = /* code to retrieve all cars */

var results = new List<Car>();

foreach (var car in allCars) 
{
  var containsAllParts = true;

  foreach (var carPart in car.Parts)
  {
    if (false == partIds.Contains(carPart.PartId))
    {
      containsAllParts = false;
      break;
    }
  }

  if (containsAllParts)
  {
    results.Add(car);
  }
}

return results;

To be clear: I want to get the Cars that have ALL of the Parts specified from the partIds array.

I have the following query, which is REALLY inefficient as it creates a subquery for each id within the partIds array and then does an IsIn query on each of their results. I am desperate to find a much more efficient manner to execute this query.

Car carAlias = null;
Part partAlias = null;

var searchCriteria = session.QueryOver<Car>(() => carAlias);

foreach (var partId in partIds)
{
  var carsWithPartCriteria = QueryOver.Of<Car>(() => carAlias)
    .JoinAlias(() => carAlias.Parts, () => partAlias)
    .Where(() => partAlias.PartId == partId)
    .Select(Projections.Distinct(Projections.Id()));

  searchCriteria = searchCriteria
    .And(Subqueries.WhereProperty(() => carAlias.Id).In(carsWithPartCriteria));
}

var results = searchCriteria.List<Car>();

Is there a decent way to execute this sort of query using NHibernate?

Answer 1

This should be exactly what you want…

Part part =  null;
Car car = null;
var qoParts = QueryOver.Of<Part>(() => part)
                .WhereRestrictionOn(x => x.PartId).IsIn(partIds)
                .JoinQueryOver(x => x.Cars, () => car)
                .Where(Restrictions.Eq(Projections.Count(() => car.CarId), partIds.Length))
                .Select(Projections.Group(() => car.CarId));