protected override Expression VisitJoin(DbJoinExpression join) { join = (DbJoinExpression)base.VisitJoin(join); if (join.Join == DbJoinType.CrossApply || join.Join == DbJoinType.OuterApply) { if (join.Right is DbTableExpression) { return(new DbJoinExpression(DbJoinType.CrossJoin, join.Left, join.Right, null)); } else { DbSelectExpression select = join.Right as DbSelectExpression; // Only consider rewriting cross apply if // 1) right side is a select // 2) other than in the where clause in the right-side select, no left-side declared aliases are referenced // 3) and has no behavior that would change semantics if the where clause is removed (like groups, aggregates, take, skip, etc). // Note: it is best to attempt this after redundant subqueries have been removed. if (select != null && select.Take == null && select.Skip == null && !AggregateChecker.HasAggregates(select) && (select.GroupBy == null || select.GroupBy.Count == 0)) { DbSelectExpression selectWithoutWhere = select.SetWhere(null); HashSet <DbTableAlias> referencedAliases = ReferencedAliasGatherer.Gather(selectWithoutWhere); HashSet <DbTableAlias> declaredAliases = DeclaredAliasGatherer.Gather(join.Left); referencedAliases.IntersectWith(declaredAliases); if (referencedAliases.Count == 0) { Expression where = select.Where; select = selectWithoutWhere; var pc = ColumnProjector.ProjectColumns(this.CanBeColumn, where, select.Columns, select.Alias, DeclaredAliasGatherer.Gather(select.From)); select = select.SetColumns(pc.Columns); where = pc.Projector; DbJoinType jt = (where == null) ? DbJoinType.CrossJoin : (join.Join == DbJoinType.CrossApply ? DbJoinType.InnerJoin : DbJoinType.LeftOuter); return(new DbJoinExpression(jt, join.Left, select, where)); } } } } return(join); }
protected override Expression VisitSelect(DbSelectExpression select) { select = (DbSelectExpression)base.VisitSelect(select); if (select.Skip != null) { DbSelectExpression newSelect = select.SetSkip(null).SetTake(null); bool canAddColumn = !select.IsDistinct && (select.GroupBy == null || select.GroupBy.Count == 0); if (!canAddColumn) { newSelect = newSelect.AddRedundantSelect(new DbTableAlias()); } newSelect = newSelect.AddColumn(new DbColumnDeclaration("rownum", new DbRowNumberExpression(select.OrderBy))); // add layer for WHERE clause that references new rownum column newSelect = newSelect.AddRedundantSelect(new DbTableAlias()); newSelect = newSelect.RemoveColumn(newSelect.Columns.Single(c => c.Name == "rownum")); var newAlias = ((DbSelectExpression)newSelect.From).Alias; DbColumnExpression rnCol = new DbColumnExpression(typeof(int), null, newAlias, "rownum"); Expression where; if (select.Take != null) { where = new DbBetweenExpression(rnCol, Expression.Add(select.Skip, Expression.Constant(1)), Expression.Add(select.Skip, select.Take)); } else { where = rnCol.GreaterThan(select.Skip); } if (newSelect.Where != null) { where = newSelect.Where.And(where); } newSelect = newSelect.SetWhere(where); select = newSelect; } return(select); }