QueryNode VisitFilter(Filter filter)
{
QueryNode result = OptimizeFilter(filter);
filter = result as Filter;
if (filter == null)
return result;
return ReorderFilter(filter);
}
/// <summary>
/// Optimizes the filter; but does not try to combine nested filter (etc.)
/// </summary>
QueryNode OptimizeFilter(Filter filter)
{
QueryNode target = Visit(filter.Target);
List<LambdaExpression> newConditions = new List<LambdaExpression>();
OptimizeQueryExpressionVisitor optimizer = new OptimizeQueryExpressionVisitor();
foreach (LambdaExpression expr in filter.Conditions) {
Expression optimizedExpr = optimizer.Visit(expr.Body);
if (optimizedExpr.NodeType == ExpressionType.Constant && optimizedExpr.Type == typeof(bool)) {
bool val = (bool)((ConstantExpression)optimizedExpr).Value;
if (val)
continue;
}
newConditions.Add(Expression.Lambda(optimizedExpr, expr.Parameters));
}
if (newConditions.Count == 0)
return target;
else
return new Filter(target, newConditions.ToArray());
}
/// <summary>
/// Tries to combine nested filters;
/// move 'MergeByName' nodes out of filter, if possible
/// </summary>
QueryNode ReorderFilter(Filter filter)
{
if (filter.Target is Filter) {
// x.Filter(y).Filter(z) -> x.Filter(y && z)
Filter innerFilter = (Filter)filter.Target;
return ReorderFilter(new Filter(innerFilter.Target, innerFilter.Conditions.Concat(filter.Conditions).ToArray()));
} else if (filter.Target is MergeByName) {
// x.MergeByName().Filter(<criteria>) -> x.Filter(x, <criteria>).MergeByName() for some safe criterias
QueryNode innerTarget = filter.Target.Target;
var conditionsToMoveIntoFilter = filter.Conditions.Where(c => IsConditionSafeVisitor.Test(c, SafeMembersForMoveIntoMergeByName)).ToArray();
if (conditionsToMoveIntoFilter.Length != 0) {
MergeByName newTarget = new MergeByName(ReorderFilter(new Filter(innerTarget, conditionsToMoveIntoFilter)));
var conditionsKeptOutsideFilter = filter.Conditions.Except(conditionsToMoveIntoFilter).ToArray();
if (conditionsKeptOutsideFilter.Length == 0)
return newTarget;
else
return new Filter(newTarget, conditionsKeptOutsideFilter);
} else {
return filter;
}
} else {
return filter;
}
}
