C# Dynamic WHERE clause in a LINQ to SQL Query

Answer 1

You could use a JOIN clause:

from pfv in dC.ProductFieldValues
join filter in filterList on (
    pfv.ProductTypeFieldID == filter.ProductTypeFieldID 
    && pfv.ValueNumber == filter.ValueNumber
)
select new ProductStruct                           
{                               
    ProductID = pfv.ProductID                           
}

Answer 2

Here is a simple example using IQueryable in VB.

Private Function GetZeroScoreWhere(ByVal qry As IQueryable(Of ScoreTest), ByVal score As ScoreTest) As IQueryable(Of ScoreTest)
    If score.CallType = ScoreTest.CallTypeEnum.XXX Then
        Return qry.Where(Function(c) c.AvgScore.Value = 0 Or c.Zero.Trim <> String.Empty)
    End If

    Return qry.Where(Function(c) c.ValidScore.Value = 0)
End Function

The same code in C#:

private IQueryable<ScoreTest> GetZeroScoreWhere(IQueryable<ScoreTest> qry, ScoreTest score)
{
    if(score.CallType == ScoreTest.CallTypeEnum.XXX)
    {
        Return qry.Where(c => c.AvgScore.Value == 0 || c.Zero.Trim != String.Empty)
    }

    Return qry.Where(c => c.ValidScore.Value == 0)    
}

Answer 3

The answer I got in a similar question worked for me:

http://stackoverflow.com/questions/180405/how-do-you-add-dynamic-where-clauses-to-a-linq-query/180475#180475

(The answer was use a Predicate Builder)