Removes one or more SelectExpression's by rewriting the expression tree to not include them, promoting their from clause expressions and rewriting any column expressions that may have referenced them to now reference the underlying data directly.
Inheritance: DbExpressionVisitor
Ejemplo n.º 1
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 protected override Expression VisitProjection(ProjectionExpression proj)
 {
     proj = (ProjectionExpression)base.VisitProjection(proj);
     if (proj.Select.From is SelectExpression)
     {
         List <SelectExpression> redundant = RedundantSubqueryGatherer.Gather(proj.Select);
         if (redundant != null)
         {
             proj = SubqueryRemover.Remove(proj, redundant);
         }
     }
     return(proj);
 }
Ejemplo n.º 2
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        protected override Expression VisitSelect(SelectExpression select)
        {
            select = (SelectExpression)base.VisitSelect(select);

            // first remove all purely redundant subqueries
            List <SelectExpression> redundant = RedundantSubqueryGatherer.Gather(select.From);

            if (redundant != null)
            {
                select = SubqueryRemover.Remove(select, redundant);
            }

            return(select);
        }
Ejemplo n.º 3
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            protected override Expression VisitSelect(SelectExpression select)
            {
                bool wasTopLevel = isTopLevel;

                isTopLevel = false;

                select = (SelectExpression)base.VisitSelect(select);

                // next attempt to merge subqueries that would have been removed by the above
                // logic except for the existence of a where clause
                while (CanMergeWithFrom(select, wasTopLevel))
                {
                    SelectExpression fromSelect = GetLeftMostSelect(select.From);

                    // remove the redundant subquery
                    select = SubqueryRemover.Remove(select, fromSelect);

                    // merge where expressions
                    Expression where = select.Where;
                    if (fromSelect.Where != null)
                    {
                        if (where != null)
                        {
                            where = fromSelect.Where.And(where);
                        }
                        else
                        {
                            where = fromSelect.Where;
                        }
                    }
                    var        orderBy    = select.OrderBy != null && select.OrderBy.Count > 0 ? select.OrderBy : fromSelect.OrderBy;
                    var        groupBy    = select.GroupBy != null && select.GroupBy.Count > 0 ? select.GroupBy : fromSelect.GroupBy;
                    Expression skip       = select.Skip != null ? select.Skip : fromSelect.Skip;
                    Expression take       = select.Take != null ? select.Take : fromSelect.Take;
                    bool       isDistinct = select.IsDistinct | fromSelect.IsDistinct;

                    if (where != select.Where ||
                        orderBy != select.OrderBy ||
                        groupBy != select.GroupBy ||
                        isDistinct != select.IsDistinct ||
                        skip != select.Skip ||
                        take != select.Take)
                    {
                        select = new SelectExpression(select.Alias, select.Columns, select.From, where, orderBy, groupBy, isDistinct, skip, take, select.IsReverse);
                    }
                }

                return(select);
            }