Lambda expression error in Linq extension

Hi guys!

I wrote my own Linq extension to filter entities by some complex criteria. Here is the code of this extension:

public static IQueryable<T> BranchFilter<T>(this IQueryable<T> source, Func<T, int> branchIdPropertySelector)
{
    try
    {
        var branches = new List<int>();

        // here is some code to fill the *branches* variable with list of branch IDs

        return source.Where(x => branches.Contains(branchIdPropertySelector(x)));
    }
    catch (Exception)
    {
        return source.Where(x => false);
    }
}

And I'm going to use it in the following way:

using (var uow = DbHelper.Context.CreateUnitOfWork())
{
    contracts = uow.Contracts.BranchFilter(x => x.BranchId).ToList();
}

Explanation: I'd like to specify in lambda the property holding Branch ID (it may differ from entity to entity) and then use this lambda in my extension to find only entities with concrete Branch IDs.

But I got the error "This expression type is not supported in LightSpeed 4.0 " [note: I'm using LS 5.0 - it seems that you need to correct also the version in constant string of your exception's message]

And here is the part of exception's stack trace:

[NotSupportedException: This expression type is not supported in LightSpeed 4.0]
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ConvertToQueryExpression(LinqQueryPlanExpression plan, Expression expression) +916
 Mindscape.LightSpeed.Linq.Sqo.<>c__DisplayClass1.<ExtractMethodCriteria>b__0(Expression e) +16
 System.Linq.WhereSelectEnumerableIterator`2.MoveNext() +145
 System.Linq.Buffer`1..ctor(IEnumerable`1 source) +216
 System.Linq.Enumerable.ToArray(IEnumerable`1 source) +77
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractMethodCriteria(LinqQueryPlanExpression plan, MethodCallExpression expression) +241
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractCriteriaCore(LinqQueryPlanExpression plan, Expression expression) +355
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractCriteria(LinqQueryPlanExpression plan, Expression expression) +59
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractCriteriaCore(LinqQueryPlanExpression plan, Expression expression) +173
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractCriteria(LinqQueryPlanExpression plan, Expression expression) +59
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractCriteriaCore(LinqQueryPlanExpression plan, Expression expression) +313
 Mindscape.LightSpeed.Linq.Sqo.CriteriaSqo.ExtractCriteria(LinqQueryPlanExpression plan, Expression expression) +59
 Mindscape.LightSpeed.Linq.Sqo.Where.ExtractWhereCriteria(MethodCallExpression expression, LinqQueryPlanExpression plan, GroupResultsPlan groupPlan) +63
 Mindscape.LightSpeed.Linq.Sqo.Where.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression) +925
 Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp) +1150
 Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp) +146
 Mindscape.LightSpeed.Linq.LinqQueryProvider.GetExecutionPlan(Expression expression) +167
 Mindscape.LightSpeed.Linq.LinqQueryProvider.Execute(Expression expression) +38
 Mindscape.LightSpeed.Linq.LinqQueryProvider.System.Linq.IQueryProvider.Execute(Expression expression) +4
 Mindscape.LightSpeed.Linq.LinqQuery`1.GetEnumerator() +18
 System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +369
 System.Linq.Enumerable.ToList(IEnumerable`1 source) +58

Can you help me please in reaching my goal?

The error is in the "where" predicate. I need to get somehow Branch ID property's value and check if it is in branches list. Please advice me how to do that?

Try extracting the branchIdPropertySelector(x) call from the Lambda method and evaluating it to a local variable inside the BranchFilter method. Then use the local variable in place of that call within your lambda. Based on the code I expect thats the unsupported aspect of the expression.

Jeremy

Thank you Jeremy for your reply!

But it seems that I can't extract branchIdPropertySelector(x) call from where clause because it should be executed for every entity inside where (to get Branch ID for every entity and decide if it is in the branches list).

If I misunderstood you could you please show me the code example reaching this?

This problem is still active. Could you advice something else?

Sorry but Im afraid this is not going to work without bringing the bulk of the query client side by forcing enumeration as we cannot evaluate the in-loop method at the server.

Jeremy