private AstPipeline OptimizeGroupStage(AstPipeline pipeline, int i, AstGroupStage groupStage)
{
try
{
if (IsOptimizableGroupStage(groupStage))
{
var followingStages = GetFollowingStagesToOptimize(pipeline, i + 1);
if (followingStages == null)
{
return(pipeline);
}
var mappings = OptimizeGroupAndFollowingStages(groupStage, followingStages);
if (mappings.Length > 0)
{
return((AstPipeline)AstNodeReplacer.Replace(pipeline, mappings));
}
}
}
catch (UnableToRemoveReferenceToElementsException)
{
// wasn't able to optimize away all references to _elements
}
return(pipeline);
static bool IsOptimizableGroupStage(AstGroupStage groupStage)
{
// { $group : { _id : ?, _elements : { $push : "$$ROOT" } } }
if (groupStage.Fields.Count == 1)
{
var field = groupStage.Fields[0];
if (field.Path == "_elements" &&
field.Value.Operator == AstAccumulatorOperator.Push &&
field.Value.Arg is AstVarExpression varExpression &&
varExpression.Name == "ROOT")
{
return(true);
}
}
return(false);
}
