Question

Using DBContext in EF5 – after filtering and partial loading based on criteria like a date range.

I’m trying to produce a complete graph or tree of objects – Persons->Events where the only Events that are included are within a date range. All this whilst preserving the standard change tracking that one gets with the following:

 Dim Repository As Models.personRepository = New Models.personRepository

 Private Sub LoadData()
    Dim personViewModelViewSource As System.Windows.Data.CollectionViewSource = CType(Me.FindResource("personViewModelViewSource"), System.Windows.Data.CollectionViewSource)
    Repository.endDate = EndDate.SelectedDate
    Repository.startDate = StartDate.SelectedDate
    personViewModelViewSource.Source = Repository.collectionOfpersons
 End Sub

A listbox and a datagrid are both bound as a proper datasource. The POCO template has been modified to put INotifyProperty events in the navigation property class, Events.

I’ve been fighting with this for days now and filtering whether on Lazy loading or Explicit loading does not function. After masses of blog/chaper reading, I’m aware of the rather unreal limitation relating to Include; instead I’m trying explicit loading. I’m using the DBContext book btw.

Being unable to bring back only a subset of the Event data from the database is 100% deal breaker as there is likely to be hundreds of thousands of Events per Person. It doesn’t make sense to me or my boss that the Entity Framework doesn’t make this functionality fairly obvious-are we missing something?

I’ve left in the commented code to try and illustrate some of the paths I’ve attempted. The class itself is a repository that this method belongs to. I’ll edit this question further to clarify just how many routes I’ve tried as it’s been a LOT. The View uses a repository layer and a ViewModel so the code behind on the XAML is rather minimal.

In advance for any help, thank you!

 Public Overridable ReadOnly Property AllFiltered(startdate As Date, enddate As Date) As ObservableCollection(Of person) Implements IpersonRepository.AllFiltered
        Get
            Dim uow = New UnitOfWork
            context = uow.Context
            Dim personQuery = context.persons.Include(Function(p) p.events).AsQueryable.Where(Function(x) x.personID = 10).FirstOrDefault


            'Dim eventQuery = From e In context.Notes
            '                 Where e.eventDateTime >= startdate And e.eventDateTime <= enddate
            '                 Select e

            'Dim personQuery As person = From r In context.persons
            '                   From e In eventQuery
            '                   Where r.personID = e.personID
            '                   Select r, e

            Dim singleperson = personQuery

            'For Each r As person In personQuery
            '    persons.Add(r)
            'Next

            '   context.Entry(eventQuery).Collection()
            ' context.Entry(personQuery).Reference(personQuery).Load()

            context.Entry(singleperson).Collection(Function(d) d.events).Query().Where(Function(x) x.eventDateTime > startdate And x.eventDateTime < enddate).Load()

            Return context.persons.Local
        End Get
    End Property

Note: I’m using logging/exception handling via PostSharp rather than polluting the code.

Below are some of the errors I’ve generated with previous paths taken.

The entity type DbQuery`1 is not part of the model for the current context.

The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties.

Parameter name: path

Unable to cast object of type ‘System.Data.Entity.Infrastructure.DbQuery1[VB$AnonymousType_02
[Entity.Person,Entity.Notes]]’ to type ‘System.Collections.ObjectModel.ObservableCollection`1[Entity.Person]’.

UPDATE: Yet another route I’ve tried, still cannot get this to fly either:

Private Property _collectionOfPersons As ObservableCollection(Of Person)

Public ReadOnly Property collectionOfPersons As ObservableCollection(Of Person)
        Get
            For Each Person In context.Persons
                _collectionOfPersons.Add(ReturnSinglePerson(startDate, endDate, Person.PersonID))
            Next
            Return _collectionOfPersons.Where(Function(x) x.events.Where(Function(e)         e.eventDateTime > startDate And e.eventDateTime < endDate))
        End Get
    End Property

Public Overridable ReadOnly Property SinglePerson(startdate As Date, enddate As Date) As ObservableCollection(Of Person) Implements IPersonRepository.AllFiltered
        Get

            Dim PersonQuery = context.Persons.Include(Function(p) p.events).AsQueryable.Where(Function(x) x.PersonID = 10).Select(Function(x) x).FirstOrDefault

            Dim Person = PersonQuery

            context.Entry(Person).Collection(Function(d) d.events).Query().Where(Function(x) x.eventDateTime > startdate And x.eventDateTime < enddate).Load()

            Return context.Persons.Local
        End Get
End Property

Public Function ReturnSinglePerson(startdate As Date, enddate As Date, id As Integer)

        Dim PersonQuery = context.Persons.Include(Function(p) p.events).AsQueryable.Where(Function(x) x.PersonID = id).Select(Function(x) x).FirstOrDefault
        Dim Person = PersonQuery
        Return Person

End Function

Another shot:
Public Overridable ReadOnly Property FilteredPersons(startdate As Date, enddate As Date) As ObservableCollection(Of Person) Implements IPersonRepository.AllFiltered
Get
context.Persons.Load()
Dim DateCriteria = Function(e) e.events.Where(Function(d) d.eventDateTime > startdate And d.eventDateTime < enddate)

            Dim Res = New ObservableCollection(Of Person)
            For Each Person In context.Persons.Local.Select(Function(x) x).Where(DateCriteria)
                Res.Add(Person)
            Next

            Return Res
        End Get
    End Property

Gives:

Public member ‘Where’ on type ‘ObservableCollection(Of DailyNotes)’ not found.

Tantalisingly close, only I get lots of duplicate names on the listbox – but the navigation carries through and the Date criteria work.

   <ExceptionAspect>
    Public Overridable ReadOnly Property FilteredPersons(startdate As Date, enddate As Date) As ObservableCollection(Of Person) Implements IPersonRepository.AllFiltered
        Get
            context.Persons.Load()


            Dim test = From r In context.Persons
                    From e In context.Notes
                    Where e.eventDateTime > startdate And e.eventDateTime < enddate
                    Join rr In context.Persons On e.PersonID Equals rr.PersonID
                    Select r, e


            Dim Res = New ObservableCollection(Of Person)
            For Each Person In test
                Res.Add(Person.r)
            Next

            Return Res
        End Get
    End Property

Don’t try this one :). It simply selects the child properties only.

    Public ReadOnly Property collectionOfResidents As ObservableCollection(Of resident)
        Get
            For Each resident In context.residents
                _collectionOfResidents.Add(ReturnSingleResident(startDate, endDate, resident.residentID))
            Next
            Return _collectionOfResidents.Select(Function(x) x.events.Where(Function(e) e.eventDateTime > startDate And e.eventDateTime < endDate))
        End Get
    End Property

I’m hoping that adding my other attempts to this question may prompt both other answers and help others see the circles they can get into when first tackling this!

Answer 1

You can use the Select clause for finer control than with Include

Something like this:

context
  .Persons
  .Where( ... some predicate on Person ... )
  .Select( o => new
    {
      Person = o,
      Events = o.Events.Where( ... some predicate on Event ... )
    }
  )
;

This will translate both predicates into SQL which execute on the database server.