protected override Expression VisitSelect(SelectExpression select)
{
// select * from table order by x skip s take t
// =>
// select * from (select top s * from (select top s + t from table order by x) order by -x) order by x
select = (SelectExpression)base.VisitSelect(select);
if (select.Skip != null && select.Take != null && select.OrderBy.Count > 0)
{
var skip = select.Skip;
var take = select.Take;
var skipPlusTake = PartialEvaluator.Eval(Expression.Add(skip, take));
select = select.SetTake(skipPlusTake).SetSkip(null);
select = select.AddRedundantSelect(this.language, new TableAlias());
select = select.SetTake(take);
// propogate order-bys to new layer
select = (SelectExpression)OrderByRewriter.Rewrite(this.language, select);
var inverted = select.OrderBy.Select(ob => new OrderExpression(
ob.OrderType == OrderType.Ascending ? OrderType.Descending : OrderType.Ascending,
ob.Expression
));
select = select.SetOrderBy(inverted);
select = select.AddRedundantSelect(this.language, new TableAlias());
select = select.SetTake(Expression.Constant(0)); // temporary
select = (SelectExpression)OrderByRewriter.Rewrite(this.language, select);
var reverted = select.OrderBy.Select(ob => new OrderExpression(
ob.OrderType == OrderType.Ascending ? OrderType.Descending : OrderType.Ascending,
ob.Expression
));
select = select.SetOrderBy(reverted);
select = select.SetTake(null);
}
return(select);
}
public override Expression ApplyPolicy(Expression expression, MemberInfo member)
{
List <LambdaExpression> ops;
if (this.policy.operations.TryGetValue(member, out ops))
{
var result = expression;
foreach (var fnOp in ops)
{
var pop = PartialEvaluator.Eval(fnOp, this.Translator.Mapper.Mapping.CanBeEvaluatedLocally);
result = this.Translator.Mapper.ApplyMapping(Expression.Invoke(pop, result));
}
var projection = (ProjectionExpression)result;
if (projection.Type != expression.Type)
{
var fnAgg = Aggregator.GetAggregator(expression.Type, projection.Type);
projection = new ProjectionExpression(projection.Select, projection.Projector, fnAgg);
}
return(projection);
}
return(expression);
}
internal IQueryProvider FindProvider(Expression expression, object[] args)
{
Expression root = this.FindProviderInExpression(expression) as ConstantExpression;
if (root == null && args != null && args.Length > 0)
{
Expression replaced = ExpressionReplacer.ReplaceAll(
expression,
this.query.Parameters.ToArray(),
args.Select((a, i) => Expression.Constant(a, this.query.Parameters[i].Type)).ToArray()
);
root = this.FindProviderInExpression(replaced);
}
if (root != null)
{
ConstantExpression cex = root as ConstantExpression;
if (cex == null)
{
cex = PartialEvaluator.Eval(root) as ConstantExpression;
}
if (cex != null)
{
IQueryProvider provider = cex.Value as IQueryProvider;
if (provider == null)
{
IQueryable query = cex.Value as IQueryable;
if (query != null)
{
provider = query.Provider;
}
}
return(provider);
}
}
return(null);
}
