52 lines
1.8 KiB
C#
52 lines
1.8 KiB
C#
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Linq.Expressions;
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using System.Data;
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namespace System.Data.Linq.SqlClient {
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using System.Data.Linq;
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/// <summary>
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/// SQL doesn't allow constants in ORDER BY.
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///
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/// Worse, an integer constant greater than 0 is treated as ORDER BY ProjectionColumn[i] so the results
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/// can be unexpected.
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///
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/// The LINQ semantic for OrderBy(o=>constant) is for it to have no effect on the ordering. We enforce
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/// that semantic here by removing all constant columns from OrderBy.
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/// </summary>
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internal class SqlRemoveConstantOrderBy {
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private class Visitor : SqlVisitor {
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internal override SqlSelect VisitSelect(SqlSelect select) {
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int i = 0;
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List<SqlOrderExpression> orders = select.OrderBy;
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while (i < orders.Count) {
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SqlExpression expr = orders[i].Expression;
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while (expr.NodeType == SqlNodeType.DiscriminatedType) {
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expr = ((SqlDiscriminatedType)expr).Discriminator;
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}
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switch (expr.NodeType) {
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case SqlNodeType.Value:
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case SqlNodeType.Parameter:
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orders.RemoveAt(i);
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break;
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default:
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++i;
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break;
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}
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}
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return base.VisitSelect(select);
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}
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}
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/// <summary>
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/// Remove relative constants from OrderBy.
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/// </summary>
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internal static SqlNode Remove(SqlNode node) {
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return new Visitor().Visit(node);
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}
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}
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}
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