Linq PredicateBuilder with conditional AND, OR and NOT filters.
- by richeym
We have a project using LINQ to SQL, for which I need to rewrite a couple of search pages to allow the client to select whether they wish to perform an and or an or search.
I though about redoing the LINQ queries using PredicateBuilder and have got this working pretty well I think. I effectively have a class containing my predicates, e.g.:
internal static Expression<Func<Job, bool>> Description(string term)
{
return p => p.Description.Contains(term);
}
To perform the search i'm doing this (some code omitted for brevity):
public Expression<Func<Job, bool>> ToLinqExpression()
{
var predicates = new List<Expression<Func<Job, bool>>>();
// build up predicates here
if (SearchType == SearchType.And)
{
query = PredicateBuilder.True<Job>();
}
else
{
query = PredicateBuilder.False<Job>();
}
foreach (var predicate in predicates)
{
if (SearchType == SearchType.And)
{
query = query.And(predicate);
}
else
{
query = query.Or(predicate);
}
}
return query;
}
While i'm reasonably happy with this, I have two concerns:
The if/else blocks that evaluate a SearchType property feel like they could be a potential code smell.
The client is now insisting on being able to perform 'and not' / 'or not' searches.
To address point 2, I think I could do this by simply rewriting my expressions, e.g.:
internal static Expression<Func<Job, bool>> Description(string term, bool invert)
{
if (invert)
{
return p => !p.Description.Contains(term);
}
else
{
return p => p.Description.Contains(term);
}
}
However this feels like a bit of a kludge, which usually means there's a better solution out there. Can anyone recommend how this could be improved? I'm aware of dynamic LINQ, but I don't really want to lose LINQ's strong typing.
