예제 #1
0
        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);
        }
예제 #2
0
        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);
        }