55 lines
1.9 KiB
C#
55 lines
1.9 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq.Expressions;
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using System.Data.Linq;
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namespace System.Data.Linq.SqlClient {
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// converts correlated scalar subqueries into outer-applies
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// must be run after flattener.
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internal class SqlRewriteScalarSubqueries {
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Visitor visitor;
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internal SqlRewriteScalarSubqueries(SqlFactory sqlFactory) {
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this.visitor = new Visitor(sqlFactory);
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}
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internal SqlNode Rewrite(SqlNode node) {
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return this.visitor.Visit(node);
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}
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class Visitor : SqlVisitor {
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SqlFactory sql;
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SqlSelect currentSelect;
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SqlAggregateChecker aggregateChecker;
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internal Visitor(SqlFactory sqlFactory) {
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this.sql = sqlFactory;
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this.aggregateChecker = new SqlAggregateChecker();
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}
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internal override SqlExpression VisitScalarSubSelect(SqlSubSelect ss) {
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SqlSelect innerSelect = this.VisitSelect(ss.Select);
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if (!this.aggregateChecker.HasAggregates(innerSelect)) {
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innerSelect.Top = this.sql.ValueFromObject(1, ss.SourceExpression);
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}
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innerSelect.OrderingType = SqlOrderingType.Blocked;
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SqlAlias alias = new SqlAlias(innerSelect);
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this.currentSelect.From = new SqlJoin(SqlJoinType.OuterApply, this.currentSelect.From, alias, null, ss.SourceExpression);
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return new SqlColumnRef(innerSelect.Row.Columns[0]);
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}
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internal override SqlSelect VisitSelect(SqlSelect select) {
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SqlSelect save = this.currentSelect;
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try {
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this.currentSelect = select;
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return base.VisitSelect(select);
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}
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finally {
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this.currentSelect = save;
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}
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}
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}
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}
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}
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