private Expression ExecuteProjection(ProjectionExpression projection, bool okayToDefer, QueryCommand command, Expression[] values)
{
okayToDefer &= (receivingMember != null && policy.IsDeferLoaded(receivingMember));
Scope saveScope = scope;
ParameterExpression reader = Expression.Parameter(typeof(FieldReader), "r" + nReaders++);
scope = new Scope(scope, reader, projection.Select.Alias, projection.Select.Columns);
LambdaExpression projector = Expression.Lambda(Visit(projection.Projector), reader);
scope = saveScope;
EntryMapping entity = EntityFinder.Find(projection.Projector);
string methExecute = okayToDefer ? "ExecuteDeferred" : "Execute";
// call low-level execute directly on supplied DbQueryProvider
Expression result = Expression.Call(executor, methExecute, new[] { projector.Body.Type }, Expression.Constant(command), projector, Expression.Constant(entity, typeof(EntryMapping)),
Expression.NewArrayInit(typeof(object), values));
if (projection.Aggregator != null)
{
// apply aggregator
result = DbExpressionReplacer.Replace(projection.Aggregator.Body, projection.Aggregator.Parameters[0], result);
}
return(result);
}
protected override Expression VisitClientJoin(ClientJoinExpression join)
{
// convert client join into a up-front lookup table builder & replace client-join in tree with lookup accessor
// 1) lookup = query.Select(e => new KVP(key: inner, value: e)).ToLookup(kvp => kvp.Key, kvp => kvp.Value)
Expression innerKey = MakeJoinKey(join.InnerKey);
Expression outerKey = MakeJoinKey(join.OuterKey);
ConstructorInfo kvpConstructor = typeof(KeyValuePair <,>).MakeGenericType(innerKey.Type, join.Projection.Projector.Type).GetConstructor(new[] { innerKey.Type, join.Projection.Projector.Type });
Expression constructKVPair = Expression.New(kvpConstructor, innerKey, join.Projection.Projector);
var newProjection = new ProjectionExpression(join.Projection.Select, constructKVPair);
int iLookup = ++nLookup;
Expression execution = ExecuteProjection(newProjection, false);
ParameterExpression kvp = Expression.Parameter(constructKVPair.Type, "kvp");
// filter out nulls
if (join.Projection.Projector.NodeType == (ExpressionType)DbExpressionType.OuterJoined)
{
LambdaExpression pred = Expression.Lambda(Expression.PropertyOrField(kvp, "Value").NotEqual(TypeHelper.GetNullConstant(join.Projection.Projector.Type)), kvp);
execution = Expression.Call(typeof(Enumerable), "Where", new[] { kvp.Type }, execution, pred);
}
// make lookup
LambdaExpression keySelector = Expression.Lambda(Expression.PropertyOrField(kvp, "Key"), kvp);
LambdaExpression elementSelector = Expression.Lambda(Expression.PropertyOrField(kvp, "Value"), kvp);
Expression toLookup = Expression.Call(typeof(Enumerable), "ToLookup", new[] { kvp.Type, outerKey.Type, join.Projection.Projector.Type }, execution, keySelector, elementSelector);
// 2) agg(lookup[outer])
ParameterExpression lookup = Expression.Parameter(toLookup.Type, "lookup" + iLookup);
PropertyInfo property = lookup.Type.GetProperty("Item");
Expression access = Expression.Call(lookup, property.GetGetMethod(), Visit(outerKey));
if (join.Projection.Aggregator != null)
{
// apply aggregator
access = DbExpressionReplacer.Replace(join.Projection.Aggregator.Body, join.Projection.Aggregator.Parameters[0], access);
}
variables.Add(lookup);
initializers.Add(toLookup);
return(access);
}
