LINQ: Dynamic predicate builder issue - linq

Question

I'm trying to create a helper class to easily build dynamic LINQ queries. Code is heavily modified version of this excellent CodeProject article: http://www.codeproject.com/Articles/493917/Dynamic-Querying-with-LINQ-to-Entities-and-Express which uses the PredicateBuilder here: http://www.albahari.com/nutshell/predicatebuilder.aspx
I'm still in the process of cleaning up the code so variables names are rubbish at the moment and there is not one comment in sight.
Usage
Dim conditions As New List(Of Condition)
With conditions
.Add(New Condition With {.Field = "EatsPeople", .Operator = "Equals", .Value = False})
.Add(New Condition With {.Field = "Name", .Operator = "Equals", .Value = "Adric"})
.Add(New Condition With {.Field = "Description", .Operator = "Contains", .Value = "ugly"})
End With
Dim predicate = BuildPredicate(conditions)
Dim tester = data.Monsters.AsExpandable.Where(predicate).ToList
Entity
Public Class Monster
Public Property EatsPeople As Boolean
Public Property Name As String
Public Property Description As String
End Class
Storage for search:
Public Class Condition
Public Property Field As String
Public Property [Operator] As String
Public Property Value As Object
End Class
Methods
Public Function BuildPredicate(conditions As List(Of Condition)) As Expression(Of Func(Of Monster, Boolean))
Dim predicate = PredicateBuilder.True(Of Monster)()
For Each c In conditions
Dim dbFieldName = c.Field
Dim dbType = GetType(Monster)
Dim dbFieldMemberInfo = dbType.GetMember(dbFieldName, BindingFlags.IgnoreCase Or BindingFlags.Public Or BindingFlags.Instance).Single()
predicate = BuildExpression(c, dbType, dbFieldMemberInfo, predicate)
Next
Return predicate
End Function
Private Function CreateLambda(value As Object, method As MethodInfo, ByVal dbType As Type, ByVal dbFieldMemberInfo As MemberInfo) As Expression(Of Func(Of Monster, Boolean))
Dim dbTypeParameter = Expression.Parameter(dbType, "x")
Dim dbFieldMember = Expression.MakeMemberAccess(dbTypeParameter, dbFieldMemberInfo)
Dim criterionConstant = New Expression() {Expression.Constant(value)}
Dim containsCall = Expression.Call(dbFieldMember, method, criterionConstant)
Return TryCast(Expression.Lambda(containsCall, dbTypeParameter), Expression(Of Func(Of Monster, Boolean)))
End Function
And the problematic method
Private Function BuildExpression(condition As Condition, ByVal dbType As Type, ByVal dbFieldMemberInfo As MemberInfo, ByVal predicate As Expression(Of Func(Of Monster, Boolean))) As Expression(Of Func(Of Monster, Boolean))
Dim type = condition.Value.GetType
Dim method As MethodInfo = type.GetMethod(condition.Operator, BindingFlags.Instance Or BindingFlags.Public, Nothing, {type}, Nothing)
If type = GetType(String) Then
If condition.Value.ToString.Contains(",") = True Then
Dim inner = PredicateBuilder.False(Of Product)()
For Each v In condition.Value.ToString.Split(",")
inner = inner.Or(CreateLambda(v, method, dbType, dbFieldMemberInfo))
Next
*****Return predicate.And(inner)*****
End If
End If
Return predicate.And(CreateLambda(condition.Value, method, dbType, dbFieldMemberInfo))
End Function
What is the problem?
The line in the last method surrounded by five asterisks is the issue.
When adding the OR grouped expression to the original predicate builder you get
The parameter 'f' was not bound in the specified LINQ to Entities
query expression.
For some reason, I can't seem to create a nested expression.
If you put the code above where the query is executed in usage sample, it works (after making some mods).
Update with solution:
The line with the asterisks needs to change to
Return predicate.And(inner.Expand)

Answer 1

I'm not a Visual Basic person, but in the C# implementation I think you'd probably need to add AsExpandable() to your query as per albahari.com/nutshell/predicatebuilder.aspx.