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);
public override AstNode VisitMapExpression(AstMapExpression node)
{
// { $map : { input : { $getField : { input : "$$ROOT", field : "_elements" } }, as : "x", in : f(x) } } => { __agg0 : { $push : f(x => root) } } + "$__agg0"
if (node.Input is AstGetFieldExpression mapInputGetFieldExpression &&
mapInputGetFieldExpression.FieldName is AstConstantExpression mapInputconstantFieldExpression &&
mapInputconstantFieldExpression.Value.IsString &&
mapInputconstantFieldExpression.Value.AsString == "_elements" &&
mapInputGetFieldExpression.Input is AstVarExpression mapInputGetFieldVarExpression &&
mapInputGetFieldVarExpression.Name == "ROOT")
{
var root = AstExpression.Var("ROOT", isCurrent: true);
var rewrittenArg = (AstExpression)AstNodeReplacer.Replace(node.In, (node.As, root));
var accumulatorExpression = AstExpression.AccumulatorExpression(AstAccumulatorOperator.Push, rewrittenArg);
var accumulatorFieldName = _accumulators.AddAccumulatorExpression(accumulatorExpression);
return(AstExpression.GetField(root, accumulatorFieldName));
}
return(base.VisitMapExpression(node));
}
public override AstNode VisitUnaryExpression(AstUnaryExpression node)
{
var root = AstExpression.Var("ROOT", isCurrent: true);
if (TryOptimizeSizeOfElements(out var optimizedExpression))
{
return(optimizedExpression);
}
if (TryOptimizeAccumulatorOfElements(out optimizedExpression))
{
return(optimizedExpression);
}
if (TryOptimizeAccumulatorOfMappedElements(out optimizedExpression))
{
return(optimizedExpression);
}
return(base.VisitUnaryExpression(node));
bool TryOptimizeSizeOfElements(out AstExpression optimizedExpression)
{
// { $size : "$_elements" } => { __agg0 : { $sum : 1 } } + "$__agg0"
if (node.Operator == AstUnaryOperator.Size)
{
if (node.Arg is AstGetFieldExpression argGetFieldExpression &&
argGetFieldExpression.FieldName is AstConstantExpression constantFieldNameExpression &&
constantFieldNameExpression.Value.IsString &&
constantFieldNameExpression.Value.AsString == "_elements")
{
var accumulatorExpression = AstExpression.AccumulatorExpression(AstAccumulatorOperator.Sum, 1);
var accumulatorFieldName = _accumulators.AddAccumulatorExpression(accumulatorExpression);
optimizedExpression = AstExpression.GetField(root, accumulatorFieldName);
return(true);
}
}
optimizedExpression = null;
return(false);
}
bool TryOptimizeAccumulatorOfElements(out AstExpression optimizedExpression)
{
// { $accumulator : { $getField : { input : "$$ROOT", field : "_elements" } } } => { __agg0 : { $accumulator : "$$ROOT" } } + "$__agg0"
if (node.Operator.IsAccumulator(out var accumulatorOperator) &&
node.Arg is AstGetFieldExpression getFieldExpression &&
getFieldExpression.FieldName is AstConstantExpression getFieldConstantFieldNameExpression &&
getFieldConstantFieldNameExpression.Value.IsString &&
getFieldConstantFieldNameExpression.Value == "_elements" &&
getFieldExpression.Input is AstVarExpression getFieldInputVarExpression &&
getFieldInputVarExpression.Name == "ROOT")
{
var accumulatorExpression = AstExpression.AccumulatorExpression(accumulatorOperator, root);
var accumulatorFieldName = _accumulators.AddAccumulatorExpression(accumulatorExpression);
optimizedExpression = AstExpression.GetField(root, accumulatorFieldName);
return(true);
}
optimizedExpression = null;
return(false);
}
bool TryOptimizeAccumulatorOfMappedElements(out AstExpression optimizedExpression)
{
// { $accumulator : { $map : { input : { $getField : { input : "$$ROOT", field : "_elements" } }, as : "x", in : f(x) } } } => { __agg0 : { $accumulator : f(x => root) } } + "$__agg0"
if (node.Operator.IsAccumulator(out var accumulatorOperator) &&
node.Arg is AstMapExpression mapExpression &&
mapExpression.Input is AstGetFieldExpression mapInputGetFieldExpression &&
mapInputGetFieldExpression.FieldName is AstConstantExpression mapInputconstantFieldExpression &&
mapInputconstantFieldExpression.Value.IsString &&
mapInputconstantFieldExpression.Value.AsString == "_elements" &&
mapInputGetFieldExpression.Input is AstVarExpression mapInputGetFieldVarExpression &&
mapInputGetFieldVarExpression.Name == "ROOT")
{
var rewrittenArg = (AstExpression)AstNodeReplacer.Replace(mapExpression.In, (mapExpression.As, root));
var accumulatorExpression = AstExpression.AccumulatorExpression(accumulatorOperator, rewrittenArg);
var accumulatorFieldName = _accumulators.AddAccumulatorExpression(accumulatorExpression);
optimizedExpression = AstExpression.GetField(root, accumulatorFieldName);
return(true);
}
optimizedExpression = null;
return(false);
}
}
