protected override Expression VisitMethodCall(MethodCallExpression node)
{
// Check if the method is SelectMany and get the collection selector
if (!QueryExpressionHelper.GetSelectManyCollectionSelector(
node,
out LambdaExpression collectionSelector))
{
return(base.VisitMethodCall(node));
}
MethodCallExpression defaultIfEmpty =
ExpressionHelper.SkipConversionNodes(collectionSelector.Body)
as MethodCallExpression;
// Check if the collection selector of the SelectMany is DefaultOrEmpty and
// get its source
if (!QueryExpressionHelper.GetDefaultOrEmptySource(defaultIfEmpty, out Expression expr))
{
return(base.VisitMethodCall(node));
}
MethodCallExpression where = expr as MethodCallExpression;
// Check if the source of DefaultOrEmpty is Where and get its predicate
if (!QueryExpressionHelper.GetWherePredicate(where, out LambdaExpression predicate))
{
return(base.VisitMethodCall(node));
}
// Get the result selector of the original SelectMany expression.
// It is used to achieve the exact same return type as the original SelectMany
// expression has.
if (!(ExpressionHelper.SkipQuoteNode(node.Arguments[2]) is LambdaExpression originalResultSelector))
{
return(base.VisitMethodCall(node));
}
// Check if the source of the Where expression contains any parameter reference
// The inner selector of the Join statement does not have parameter, so if the
// source refers the parameter somewhere, it cannot be used as source
bool parameterReferred = ExpressionSearchVisitor.Search(
where.Arguments[0],
collectionSelector.Parameters[0]);
if (parameterReferred)
{
return(base.VisitMethodCall(node));
}
// Analyse the predicate, find key mapping
EqualityMappingDetector detector =
new EqualityMappingDetector(
collectionSelector.Parameters[0],
predicate.Parameters[0]);
if (!detector.Detect(predicate.Body))
{
// Cannot convert the predicate into join
return(base.VisitMethodCall(node));
}
// Everything is appropriate for a conversion, visit the inner and outer sources
Expression outerSource = this.Visit(node.Arguments[0]);
Expression innerSource = this.Visit(where.Arguments[0]);
// Inner and outer entity types
Type outerType = collectionSelector.Parameters[0].Type;
Type innerType = predicate.Parameters[0].Type;
LinqJoinKeyHelper.CreateKeySelectors(
outerType,
innerType,
detector.LeftMembers,
detector.RightMembers,
out LambdaExpression outerKey,
out LambdaExpression innerKey);
// Create the result selector of the GroupJoin
LambdaExpression groupJoinResultSelector =
CreateGroupJoinResultSelector(outerType, innerType);
Type groupJoinResultType = groupJoinResultSelector.Body.Type;
// Create the GroupJoin method definition
// Generic arguments:
// Outer entity type (same as in SelectMany)
// Inner entity type (same as in SelectMany)
// Key type
// Result type (custom tuple)
MethodInfo groupJoinMethod =
QueryMethods.GroupJoin.MakeGenericMethod(
node.Method.GetGenericArguments()[0],
node.Method.GetGenericArguments()[1],
outerKey.Body.Type,
groupJoinResultType);
// Create the Join call expression
// Arguments:
// Outer collection (visited source of SelectMany expression)
// Inner collection (visited source of the Where expression)
// Outer key selector
// Inner key selector
// Result selector (tuple)
Expression groupJoin = Expression.Call(
groupJoinMethod,
outerSource,
innerSource,
Expression.Quote(outerKey),
Expression.Quote(innerKey),
Expression.Quote(groupJoinResultSelector));
// Collection selector for the post SelectMany expression
LambdaExpression postSelectManyCollectionSelector =
CreatePostSelectManyCollectionSelector(
innerType,
groupJoinResultType);
// Result selector for the post SelectMany expression.
LambdaExpression postSelectManyResultSelector =
CreatePostSelectManyResultSelector(
innerType,
groupJoinResultType,
originalResultSelector);
// Define the method of the post SelectMany.
// Generic arguments:
// Result type of the GroupJoin
// Inner entity type
// Result type (same as the original SelectMany)
MethodInfo postSelectManyMethod =
QueryMethods.SelectMany.MakeGenericMethod(
groupJoinResultType,
node.Method.GetGenericArguments()[1],
node.Method.GetGenericArguments()[2]);
Expression postSelectMany =
Expression.Call(
postSelectManyMethod,
groupJoin,
Expression.Quote(postSelectManyCollectionSelector),
Expression.Quote(postSelectManyResultSelector));
return(postSelectMany);
}
protected override Expression VisitMethodCall(MethodCallExpression node)
{
// Check if the method is SelectMany and get the collection selector
if (!QueryExpressionHelper.GetSelectManyCollectionSelector(
node,
out LambdaExpression collectionSelector))
{
return(base.VisitMethodCall(node));
}
// Unwrap the selector (hopefully Where expression)
MethodCallExpression where =
ExpressionHelper.SkipConversionNodes(collectionSelector.Body)
as MethodCallExpression;
// Check if the selector of SelectMany is Where and get the predicate
if (!QueryExpressionHelper.GetWherePredicate(where, out LambdaExpression predicate))
{
return(base.VisitMethodCall(node));
}
// Check if the source of the Where expression contains any parameter reference
// The inner selector of the Join statement does not have parameter, so if the
// source refers the parameter somewhere, it cannot be used as source
bool parameterReferred = ExpressionSearchVisitor.Search(
where.Arguments[0],
collectionSelector.Parameters[0]);
if (parameterReferred)
{
return(base.VisitMethodCall(node));
}
// Analyse the predicate, find key mapping
EqualityMappingDetector detector =
new EqualityMappingDetector(
collectionSelector.Parameters[0],
predicate.Parameters[0]);
if (!detector.Detect(predicate.Body))
{
// Cannot convert the predicate into join
return(base.VisitMethodCall(node));
}
// Everything is appropriate for a conversion, visit the inner and outer sources
Expression outerSource = this.Visit(node.Arguments[0]);
Expression innerSource = this.Visit(where.Arguments[0]);
// Inner and outer entity types
Type outerType = collectionSelector.Parameters[0].Type;
Type innerType = predicate.Parameters[0].Type;
LinqJoinKeyHelper.CreateKeySelectors(
outerType,
innerType,
detector.LeftMembers,
detector.RightMembers,
out LambdaExpression outerKey,
out LambdaExpression innerKey);
// Create the Join method definition:
// It has the same generic type arguments as the SelectMany
// Only add the key type (third argument)
MethodInfo joinMethod = QueryMethods.Join.MakeGenericMethod(
node.Method.GetGenericArguments()[0],
node.Method.GetGenericArguments()[1],
outerKey.Body.Type,
node.Method.GetGenericArguments()[2]);
// Create the Join call expression
// Arguments:
// Outer collection (visited source of SelectMany expression)
// Inner collection (visited source of the Where expression)
// Outer key selector
// Inner key selector
// Result selector (same as the SeletMany result selector)
return(Expression.Call(
joinMethod,
outerSource,
innerSource,
Expression.Quote(outerKey),
Expression.Quote(innerKey),
node.Arguments[2]));
}