Question

We have a complex business model and is using NHibernate to create and maintain the database. This results in poor performance from time to time when a fairly straight forward query results in a large object graph.

Usually we are able to rewrite the query and gain a good performance boost while at the same time getting to know the business model better. However now we have stumbled over a case where we are unable to get a better result that what we currently have which, frankly, is really really poor.

We have the following classes with associated mappings. The classes have been stripped down to minimum just let me know if you need more information.

public class GraphPoint
{
   public DateTime datum;
   public IDictionary<Avtal, Value> values;
   public Calculation calculation;
   public bool isCalculated;
   public Int64 graphPointId;

   ...
}

public class Value
{
   public int numbers;
   public int points;
}

public class Avtal
{
   public string name;
   public Int64 avtalId

   ...
}

<class name="GraphPoint" lazy="false">
   <id name="GraphPointId" column="GraphPointId" type="Int64">
     <generator class="Business.Data.IncrementGenerator, Business"/>
   </id>

   <property name="Datum" not-null="true" unique-key="UIX1_GraphPoint" />
   <map name="Values" table="GraphPointValue" cascade="all-delete-orphan">
     <key column="GraphPointId" foreign-key="FK_GraphPoint_GraphPointValue" />
     <map-key-many-to-many class="Avtal" column="AvtalId" 
                           foreign-key="FK_GraphPoint_GraphPointValue_Avtal"  />
     <composite-element class="GraphPoint+Value">
       <property name="Numbers" not-null="true" />
       <property name="Points" not-null="true" precision="26" scale="15" />
     </composite-element>
   </map>
   <property name="IsCalculated" not-null="true" />
   <many-to-one name="Calculation" column="CalculationId" 
                foreign-key="FK_Calculation_GraphPoint" />
</class>

So in this scenario we the following criterias:
* Return all GraphPointValues between two dates
* Aggregate these based on the Avtal object

We currently have been trying with this:

from punkt in (from punkt in Session.Query<GraphPoint>()
               where punkt.IsCalculated && 
                     punkt.Datum >= lowDate && 
                     punkt.Datum <= highDate
               select punkt).ToArray()
let values = from value in punkt.Values
             where forAvtal.Contains(value.Key.AvtalId)
             select value.Value
select new GraphPointValuePresentationObject
{
   Datum = punkt.Datum,
   Numbers = värden.Sum(v => v.Antal),
   Points = värden.Sum(v => v.Poäng),
   IsCalculated = punkt.IsCalculated
}

forAvtal is a list containing id’s for these objects that shoudl be met.

When we run this we get one sql-statement against the database which fetches all the GraphPoints that lay between the dates and then we get one sql-statment for each and everyone of the points that the first sql-statement returns.

I want to rewrite this so that we only need a couple of sql-statements and not several hundreds as it is today. Can anyone give me a pointer in the right direction, I’ve tried Critierias and DetachedQueries but can’t get it to work as I want to.

Answer 1

inserting .Fetch(x => x.Values) befor .ToArray() should do the trick. It will generate a join to fetch all related values along with the Graphpoints