Question

EDIT: More detailed question.

I am working on batched operations in nHibernate, specifically for In queries to overcome the 2100 parameter limit size in SQL Server.

For this, I have created a class with this constructor (this is a very simplified version):

BatchedQuery(session.Query<Foo>(), allValues, (l, e) => l.Contains(e.Id));

...

public BatchedQuery(IQueryable<TEntity> query, IList<TValue> allValues, Expression<Func<IList<TValue>, TEntity, bool>> predicate)
{
   List<TValue> values = ...; // Select a batch from allValues
   ...

   // I want to pass the values to the expression passed in...
   // something like this, without using Compile: 
   // e => predicate.Compile()(values, e)

   // using JKor's method, I tried this...
   ParameterExpression param = Expression.Parameter(typeof(TEntity), "e");
   Expression<Func<TEntity, bool>> expr2 =
       Expression.Lambda<Func<TEntity, bool>>(Expression.Invoke(predicate,
           Expression.Constant(batchOfValues), param), param);

   query = query.Where(expr2);

   // Do something with the query...
}

// Somewhere else..
// This causes the exception
batchedQuery.ToList();

The above is causing nHibernate to throw a KeyNotFoundException.

Here is the stack trace:

at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
at NHibernate.Param.NamedParameterSpecification.SetEffectiveType(QueryParameters queryParameters)
at NHibernate.Param.ParametersBackTrackExtensions.ResetEffectiveExpectedType(IEnumerable`1 parameterSpecs, QueryParameters queryParameters)
at NHibernate.Hql.Ast.ANTLR.Loader.QueryLoader.ResetEffectiveExpectedType(IEnumerable`1 parameterSpecs, QueryParameters queryParameters)
at NHibernate.Loader.Loader.CreateSqlCommand(QueryParameters queryParameters, ISessionImplementor session)
at NHibernate.Impl.MultiQueryImpl.AggregateQueriesInformation()
at NHibernate.Impl.MultiQueryImpl.get_Parameters()
at NHibernate.Impl.MultiQueryImpl.CreateCombinedQueryParameters()
at NHibernate.Impl.MultiQueryImpl.List()
at NHibernate.Impl.FutureQueryBatch.GetResultsFrom(IMultiQuery multiApproach)
at NHibernate.Impl.FutureBatch`2.GetResults()
at NHibernate.Impl.FutureBatch`2.get_Results()
at NHibernate.Impl.FutureBatch`2.GetCurrentResult[TResult](Int32 currentIndex)
at NHibernate.Impl.FutureBatch`2.<>c__DisplayClass4`1.<GetEnumerator>b__3()
at NHibernate.Impl.DelayedEnumerator`1.<get_Enumerable>d__0.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at NovusERP.Data.Helpers.BatchedQuery`2.ToList() in D:\Short Utilities\Novus\NovusERP\NovusERP.Data\Helpers\BatchedQuery.cs:line 63
at NovusERP.Modules.Payroll.Attendance.AttendanceViewModel.GetEmployees(IList`1 selectedEmployeeIds) in D:\Short Utilities\Novus\NovusERP\NovusERP.Modules\Payroll\Attendance\AttendanceViewModel.cs:line 79
at NovusERP.Modules.Payroll.Attendance.AttendanceViewModel..ctor(MonthYear currentMonth, IList`1 selectedEmployeeIds) in D:\Short Utilities\Novus\NovusERP\NovusERP.Modules\Payroll\Attendance\AttendanceViewModel.cs:line 47
at NovusERP.Modules.Payroll.Attendance.AttendanceView..ctor(MonthYear currentMonth, IList`1 selectedEmployees) in D:\Short Utilities\Novus\NovusERP\NovusERP.Modules\Payroll\Attendance\AttendanceView.xaml.cs:line 18
at lambda_method(Closure , Object[] )
at Autofac.Core.Activators.Reflection.ConstructorParameterBinding.Instantiate()

Can anybody point me to the right direction? Any help will be highly appreciated.

Regards,
Yogesh.

Answer 1

I am posting my answer so that others can benefit from it.

The best way to do what I wanted was to use ExpressionVisitor and Expression.Lambda and make a copy of the whole expression with the appropriate changes. This class is an internal class in 3/3.5, so if you want to use this class for 3/3.5, here is the complete implementation of the class. There are tons of tutorials available for the same on the net.

Secondly, anyone who wants to get a tool for parsing and visualizing expression trees should get the ExpressionTreeVisualizer sample in VS 2008. You will have to convert and compile the sample to VS 2010 for .Net 4.0. This blog post by Patrick Smacchia helps you how.

One side note to all of the above, nhibernate still throws the exception even after converting the query the way I have explained in this answer. This only happens if I try to convert the query to a future query and then evaluate it. Without converting the query to future, it works fine. I am searching for a solution for the same. I will update the answer accordingly if I find out why it is happening and what is the solution.