protected override Expression VisitClientJoin(ClientJoinExpression join)
{
// convert client join into a up-front lookup table builder and 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);
ProjectionExpression newProjection = new ProjectionExpression(join.Projection.Source, 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.NotEqual(
Expression.PropertyOrField(kvp, "Value"),
Expression.Constant(null, 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);
}
protected virtual Expression VisitClientJoin(ClientJoinExpression join)
{
ProjectionExpression projection = (ProjectionExpression)this.Visit(join.Projection);
var outerKey = this.VisitExpressionList(join.OuterKey);
var innerKey = this.VisitExpressionList(join.InnerKey);
if (projection != join.Projection || outerKey != join.OuterKey || innerKey != join.InnerKey)
{
return(new ClientJoinExpression(projection, outerKey, innerKey));
}
return(join);
}
protected virtual Expression VisitClientJoin(ClientJoinExpression join)
{
this.AddAlias(join.Projection.Source.Alias);
this.Write("ClientJoin(");
this.WriteLine(Indentation.Inner);
this.Write("OuterKey(");
this.VisitExpressionList(join.OuterKey);
this.Write("),");
this.WriteLine(Indentation.Same);
this.Write("InnerKey(");
this.VisitExpressionList(join.InnerKey);
this.Write("),");
this.WriteLine(Indentation.Same);
this.Visit(join.Projection);
this.WriteLine(Indentation.Outer);
this.Write(")");
return(join);
}