Issue with Contains()

[mahara]

Hi,

I have an issue with Contains() given the following LINQ:

session.Query().Where(x => ids.Contains(x.Id).ToList();

where ids is a list/collection of document ID to be queried.

Is this a supported scenario?

Here's the exception details:

The binary operator Equal is not defined for the types 'System.Collections.Generic.List`1[System.Int64]' and 'System.Int64'.

--- EXCEPTION #1/1 <InvalidOperationException>
Message = "The binary operator Equal is not defined for the types 'System.Collections.Generic.List`1[System.Int64]' and 'System.Int64'."
ClassName = System.InvalidOperationException
HResult = -2146233079
Source = System.Core
StackTrace =
   at System.Linq.Expressions.Expression.GetEqualityComparisonOperator(ExpressionType binaryType, String opName, Expression left, Expression right, Boolean liftToNull)
   at System.Linq.Expressions.Expression.Equal(Expression left, Expression right, Boolean liftToNull, MethodInfo method)
   at System.Linq.Expressions.Expression.MakeBinary(ExpressionType binaryType, Expression left, Expression right, Boolean liftToNull, MethodInfo method, LambdaExpression conversion)
   at Lucene.Net.Linq.Transformation.TreeVisitors.SubQueryContainsTreeVisitor.VisitSubQueryExpression(SubQueryExpression expression)
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression)
   at Remotion.Linq.Clauses.WhereClause.TransformExpressions(Func`2 transformation)
   at Lucene.Net.Linq.Transformation.QueryModelTransformer.VisitWhereClause(WhereClause whereClause, QueryModel queryModel, Int32 index)
   at Remotion.Linq.Clauses.WhereClause.Accept(IQueryModelVisitor visitor, QueryModel queryModel, Int32 index)
   at Remotion.Linq.QueryModelVisitorBase.VisitBodyClauses(ObservableCollection`1 bodyClauses, QueryModel queryModel)
   at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
   at Remotion.Linq.QueryModel.Accept(IQueryModelVisitor visitor)
   at Lucene.Net.Linq.LuceneQueryExecutorBase`1.PrepareQuery(QueryModel queryModel)
   at Lucene.Net.Linq.LuceneQueryExecutorBase`1.<ExecuteCollection>d__3`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

[chriseldredge]

This is not supported. It could probably be implemented, but Lucene does not support a query like this natively. Probably the approach would be to generate a Boolean query testing a field against each distinct value in the collection.

The best work around at the moment is probably something like:

var query = session.Query();
var docs = ids.Select(i => query.Where(d => d.Id == i).SingleOrDefault()).ToList();

This would execute a single query for each id instead of executing them all in a single query. Without profiling I'm not sure how much advantage there would be to try to do them all in a single query.

[mahara]

IC.

Yup, that's what basically I'm doing, querying document per its ID. I'm just looking for if there were any better and performant way in doing that.

Thanks for the clarification!