Left outer join LINQ errors when selecting strongly typed result

Hi

This query works:

      var r = (from ma in UnitOfWork.MediaAssets
               join i in UnitOfWork.MediaAssetSetItems on ma.Id equals i.MediaAssetId
               join a in UnitOfWork.MediaAssetSetItemApprovals on i.Id equals a.MediaAssetSetItemId into temp
               where i.MediaAssetSetId == mediaAssetSetId
               from a1 in temp.DefaultIfEmpty()
               select new
                 {
                   MediaAssetId = ma.Id,
                   AssetPath = ma.AssetPath,
                   SortOrder = i.SortOrder,
                   Name = i.Name,
                   MediaAssetSetItemId = i.Id,
                   ApproveCount = i.ApproveCount,
                   DisapproveCount = i.DisapproveCount,
                   IsApprove = (bool?) a1.IsApprove
                 }).ToList();

But this one breaks:

      var r = (from ma in UnitOfWork.MediaAssets
               join i in UnitOfWork.MediaAssetSetItems on ma.Id equals i.MediaAssetId
               join a in UnitOfWork.MediaAssetSetItemApprovals on i.Id equals a.MediaAssetSetItemId into temp
               where i.MediaAssetSetId == mediaAssetSetId
               from a1 in temp.DefaultIfEmpty()
               select new MediaAssetSetItemSummary
                 {
                   MediaAssetId = ma.Id,
                   AssetPath = ma.AssetPath,
                   SortOrder = i.SortOrder,
                   Name = i.Name,
                   MediaAssetSetItemId = i.Id,
                   ApproveCount = i.ApproveCount,
                   DisapproveCount = i.DisapproveCount,
                   IsApprove = (bool?) a1.IsApprove
                 }).ToList();

The only difference is the first one selects an anonymous object, the second one selects a strongly typed result (MediaAssetSetItemSummary).

Here's the error:

System.Reflection.TargetInvocationException : Exception has been thrown by the target of an invocation.
  ----> System.NullReferenceException : Object reference not set to an instance of an object.
    at System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner)
    at System.RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner)
    at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
    at System.Delegate.DynamicInvokeImpl(Object[] args)
    at Mindscape.LightSpeed.Linq.ProjectManyProjectionChain.Apply(EntityTuple set, Int32 index)
    at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.ProjectMany(EntityTuple set, IList`1 projectors, IList`1 projectionMappings, Boolean distinct)
    at Mindscape.LightSpeed.Linq.Plan.SingleQueryPlan.ExecuteImmediate(IUnitOfWork unitOfWork, Type returnType)
    at Mindscape.LightSpeed.Linq.LinqQueryProvider.Execute(Expression expression)
    at Mindscape.LightSpeed.Linq.LinqQueryProvider.System.Linq.IQueryProvider.Execute(Expression expression)
    at Mindscape.LightSpeed.Linq.LinqQuery`1.GetEnumerator()
    at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
    Repositories\MediaAssetRepository.cs(179,0): at Blc.Common.Model.Repositories.MediaAssetRepository.GetMediaAssetSetItemSummaries(Guid mediaAssetSetId)
    Repositories\MediaAssetRepositoryTests.cs(21,0): at Blc.Common.Model.Tests.Repositories.MediaAssetRepositoryTests.GetMediaAssetSetItemSummaries()
    --NullReferenceException
    at lambda_method(Closure , <>f__AnonymousType17`2 , MediaAssetSetItemApproval )

I found another bug. When joining on two variables in LINQ and one of those variables is a constant then an error is thrown:

      Guid d = Guid.NewGuid();

      var r = (from ma in UnitOfWork.MediaAssets
               join i in UnitOfWork.MediaAssetSetItems on ma.Id equals i.MediaAssetId
               join a in UnitOfWork.MediaAssetSetItemApprovals on new { i.Id, CreatedByUserId = d } equals new { Id = a.MediaAssetSetItemId, a.CreatedByUserId } into temp
               where i.MediaAssetSetId == mediaAssetSetId
               from a1 in temp.DefaultIfEmpty()
               select new
                 {
                   MediaAssetId = ma.Id,
                   AssetPath = ma.AssetPath,
                   SortOrder = i.SortOrder,
                   Name = i.Name,
                   MediaAssetSetItemId = i.Id,
                   ApproveCount = i.ApproveCount,
                   DisapproveCount = i.DisapproveCount,
                   IsApprove = (bool?) a1.IsApprove
                 }).ToList();

The error:

System.NullReferenceException : Object reference not set to an instance of an object.
    at Mindscape.LightSpeed.Linq.Sqo.JoinBase.ExtractJoinConditions(LinqQueryPlanExpression plan, Expression lhsCriteriaExpression, Expression rhsCriteriaExpression, Selectable rhsSelectable)
    at Mindscape.LightSpeed.Linq.Sqo.GroupJoin.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression)
    at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp)
    at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp)
    at Mindscape.LightSpeed.Linq.Sqo.Where.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression)
    at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp)
    at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp)
    at Mindscape.LightSpeed.Linq.Sqo.SelectMany.EvaluateDefaultIfEmpty(ExpressionVisitor visitor, MethodCallExpression expression)
    at Mindscape.LightSpeed.Linq.Sqo.SelectMany.Evaluate(ExpressionVisitor visitor, MethodCallExpression expression)
    at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.VisitMethodCall(MethodCallExpression exp)
    at Mindscape.LightSpeed.Linq.Plan.LinqQueryBuilder.Visit(Expression exp)
    at Mindscape.LightSpeed.Linq.LinqQueryProvider.GetExecutionPlan(Expression expression)
    at Mindscape.LightSpeed.Linq.LinqQueryProvider.Execute(Expression expression)
    at Mindscape.LightSpeed.Linq.LinqQueryProvider.System.Linq.IQueryProvider.Execute(Expression expression)
    at Mindscape.LightSpeed.Linq.LinqQuery`1.GetEnumerator()
    at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

Hi James,

We have added in a fix for the original issue around the error occuring when projecting to a strongly typed result. This will be available in the next nightly build.

Jeremy

For the issue you are seeing with joining on constants, currently this is not supported. Only joins between entity properties (which ultimately will map to database columns) are supported.

The error message here could most definitely be a bit clearer about that so Ill look at adding some better checks to handle that. That said, I am keen to extend support to include constants but this is not something that will be quick to implement. Im going to have a look at this over the next few days to see if we can get this in, will keep you posted.

Jeremy

Ok.

This isn't that important, I might rewrite it as a SQL stored proc. Figured you would want to know about the bugs I found along the way.

Hi again

I've found some places where I need to use a constant in a join. Could you look into this and let me know when it could be added? I'd rather use LINQ than make stored procedures each time.