'<FieldName>' is not a member of type '<Type>' in the currently loaded schemas

I have the following function defined in the CSDL of my EDMX.

<Function Name="GetSprintDuration" ReturnType="Edm.Decimal">
     <Parameter Name="sprintId" Type="Edm.Int32" />
     <DefiningExpression>
          SUM( SELECT VALUE h.Duration
          FROM ApplicationEntities.Hours as h
          WHERE h.Story.Project.SprintId = sprintId)
     </DefiningExpression>
</Function>

My code for accessing the function looks like:

[EdmFunction("ApplicationModel", "GetSprintDuration")]
public decimal? GetSprintDuration(int sprintId)
{
    return this.QueryProvider.Execute<decimal?>(Expression.Call(
    Expression.Constan开发者_如何转开发t(this),
    (MethodInfo)MethodInfo.GetCurrentMethod(),
    Expression.Constant(sprintId, typeof(int))));
}

When I call this method I receive the following error:

'SprintId' is not a member of type 'ApplicationModel.Project' in the currently loaded schemas.

The error is being generated when the QueryProvider.Execute is called:

Line 17:         public decimal? GetSprintDuration(int sprintId)
Line 18:         {
Line 19:             return this.QueryProvider.Execute<decimal?>(Expression.Call(
Line 20:                 Expression.Constant(this),
Line 21:                 (MethodInfo)MethodInfo.GetCurrentMethod(),

If I change the function to something like:

<Function Name="GetSprintDuration" ReturnType="Edm.Decimal">
     <Parameter Name="sprintId" Type="Edm.Int32" />
     <DefiningExpression>
          SUM( SELECT VALUE h.Duration
          FROM ApplicationEntities.Hours as h
          WHERE h.HourId != 0)
     </DefiningExpression>
</Function>

My application functions as normal ... for some reason I don't have access to the full entity model. Is there a way to make it so that I can access the full entity model OR is this not possible?

Thanks in advance!

---

With the help of @Henk Holterman I was able to figure my problem out ... I didn't realize that ESQL supported JOINS, so here is what the working code looks like:

   <Function Name="GetSprintDuration" ReturnType="Edm.Decimal">
      <Parameter Name="sprintId" Type="Edm.Int32" />
      <DefiningExpression>
        SUM( SELECT VALUE h.Duration
        FROM ApplicationEntities.Hours as h 
        JOIN ApplicationEntities.Stories as s on h.StoryId == s.StoryId
        WHERE s.SprintId == sprintId )
      </DefiningExpression>
    </Function>