예제 #1
0
        private Expression MakeSubquery(Expression expression)
        {
            var newAlias = new TableAlias();
            HashSet <TableAlias> aliases = DeclaredAliasGatherer.Gather(expression);

            var decls = new List <ColumnDeclaration>();

            foreach (TableAlias ta in aliases)
            {
                foreach (ColumnExpression col in columns[ta])
                {
                    string name = decls.GetAvailableColumnName(col.Name);
                    var    decl = new ColumnDeclaration(name, col, col.QueryType);
                    decls.Add(decl);
                    var newCol = new ColumnExpression(col.Type, col.QueryType, newAlias, col.Name);
                    map.Add(col, newCol);
                }
            }

            return(new SelectExpression(newAlias, decls, expression, null));
        }
예제 #2
0
 protected override Expression VisitJoin(JoinExpression join)
 {
     join = (JoinExpression)base.VisitJoin(join);
     if (join.Join == JoinType.CrossJoin && currentWhere != null)
     {
         // try to figure out which parts of the current where expression can be used for a join condition
         HashSet <TableAlias> declaredLeft  = DeclaredAliasGatherer.Gather(join.Left);
         HashSet <TableAlias> declaredRight = DeclaredAliasGatherer.Gather(join.Right);
         var               declared         = new HashSet <TableAlias>(declaredLeft.Union(declaredRight));
         Expression[]      exprs            = currentWhere.Split(ExpressionType.And, ExpressionType.AndAlso);
         List <Expression> good             = exprs.Where(e => CanBeJoinCondition(e, declaredLeft, declaredRight, declared)).ToList();
         if (good.Count > 0)
         {
             Expression condition = good.Join(ExpressionType.And);
             join = UpdateJoin(join, JoinType.InnerJoin, join.Left, join.Right, condition);
             Expression newWhere = exprs.Where(e => !good.Contains(e)).Join(ExpressionType.And);
             currentWhere = newWhere;
         }
     }
     return(join);
 }
예제 #3
0
        protected override Expression VisitJoin(JoinExpression join)
        {
            join = (JoinExpression)base.VisitJoin(join);

            if (join.Join == JoinType.CrossApply || join.Join == JoinType.OuterApply)
            {
                if (join.Right is TableExpression)
                {
                    return(new JoinExpression(JoinType.CrossJoin, join.Left, join.Right, null));
                }
                else
                {
                    var select = join.Right as SelectExpression;
                    // 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))
                    {
                        SelectExpression     selectWithoutWhere = select.SetWhere(null);
                        HashSet <TableAlias> referencedAliases  = ReferencedAliasGatherer.Gather(selectWithoutWhere);
                        HashSet <TableAlias> declaredAliases    = DeclaredAliasGatherer.Gather(join.Left);
                        referencedAliases.IntersectWith(declaredAliases);
                        if (referencedAliases.Count == 0)
                        {
                            Expression where = select.Where;
                            select           = selectWithoutWhere;
                            ProjectedColumns pc = ColumnProjector.ProjectColumns(language, where, select.Columns, select.Alias, DeclaredAliasGatherer.Gather(select.From));
                            select = select.SetColumns(pc.Columns);
                            where  = pc.Projector;
                            JoinType jt = (where == null) ? JoinType.CrossJoin : (join.Join == JoinType.CrossApply ? JoinType.InnerJoin : JoinType.LeftOuter);
                            return(new JoinExpression(jt, join.Left, select, where));
                        }
                    }
                }
            }

            return(join);
        }