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164
MarkMpn.Sql4Cds.Engine/Visitors/RemoveRecursiveCTETableReferencesVisitor.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,164 @@ | ||
| using System; | ||
| using System.Collections.Generic; | ||
| using System.Text; | ||
| using Microsoft.SqlServer.TransactSql.ScriptDom; | ||
|
|
||
| namespace MarkMpn.Sql4Cds.Engine.Visitors | ||
| { | ||
| /// <summary> | ||
| /// Finds recursive references in a CTE definition and removes them, moving join predicates to the WHERE clause | ||
| /// </summary> | ||
| class RemoveRecursiveCTETableReferencesVisitor : TSqlConcreteFragmentVisitor | ||
| { | ||
| private readonly string _name; | ||
| private readonly string[] _columnNames; | ||
| private readonly Dictionary<string, string> _outerReferences; | ||
| private BooleanExpression _joinPredicate; | ||
| private int _inUnqualifiedJoin; | ||
|
|
||
| public RemoveRecursiveCTETableReferencesVisitor(string name, string[] columnNames, Dictionary<string, string> outerReferences) | ||
| { | ||
| _name = name; | ||
| _columnNames = columnNames; | ||
| _outerReferences = outerReferences; | ||
| } | ||
|
|
||
| private bool IsRecursiveReference(TableReference tableReference) | ||
| { | ||
| if (!(tableReference is NamedTableReference namedTable)) | ||
| return false; | ||
|
|
||
| if (namedTable.SchemaObject.Identifiers.Count != 1) | ||
| return false; | ||
|
|
||
| return namedTable.SchemaObject.BaseIdentifier.Value.Equals(_name, StringComparison.OrdinalIgnoreCase); | ||
| } | ||
|
|
||
| private InlineDerivedTable CreateInlineDerivedTable() | ||
| { | ||
| var table = new InlineDerivedTable | ||
| { | ||
| Alias = new Identifier { Value = _name }, | ||
| RowValues = { new RowValue() } | ||
| }; | ||
|
|
||
| foreach (var col in _columnNames) | ||
| { | ||
| table.Columns.Add(new Identifier { Value = col }); | ||
| table.RowValues[0].ColumnValues.Add(new VariableReference { Name = _outerReferences[col] }); | ||
| } | ||
|
|
||
| return table; | ||
| } | ||
|
|
||
| private bool RemoveRecursiveJoin(TableReference tableReference, out TableReference removed) | ||
| { | ||
| removed = null; | ||
|
|
||
| if (!(tableReference is JoinTableReference join)) | ||
| return false; | ||
|
|
||
| if (IsRecursiveReference(join.FirstTableReference)) | ||
| { | ||
| if (_inUnqualifiedJoin > 0) | ||
| { | ||
| join.FirstTableReference = CreateInlineDerivedTable(); | ||
| return false; | ||
| } | ||
|
|
||
| _joinPredicate = (join as QualifiedJoin)?.SearchCondition; | ||
| removed = join.SecondTableReference; | ||
| return true; | ||
| } | ||
|
|
||
| if (IsRecursiveReference(join.SecondTableReference)) | ||
| { | ||
| if (_inUnqualifiedJoin > 0) | ||
| { | ||
| join.SecondTableReference = CreateInlineDerivedTable(); | ||
| return false; | ||
| } | ||
|
|
||
| _joinPredicate = (join as QualifiedJoin)?.SearchCondition; | ||
| removed = join.FirstTableReference; | ||
| return true; | ||
| } | ||
|
|
||
| return false; | ||
| } | ||
|
|
||
| public override void Visit(FromClause node) | ||
| { | ||
| base.Visit(node); | ||
|
|
||
| for (var i = 0; i < node.TableReferences.Count; i++) | ||
| { | ||
| if (IsRecursiveReference(node.TableReferences[i])) | ||
| { | ||
| if (_inUnqualifiedJoin > 0) | ||
| node.TableReferences[i] = CreateInlineDerivedTable(); | ||
| else | ||
| node.TableReferences.RemoveAt(i); | ||
| } | ||
| else if (RemoveRecursiveJoin(node.TableReferences[i], out var removed)) | ||
| { | ||
| node.TableReferences[i] = removed; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| public override void Visit(QualifiedJoin node) | ||
| { | ||
| base.Visit(node); | ||
|
|
||
| if (RemoveRecursiveJoin(node.FirstTableReference, out var removed)) | ||
| node.FirstTableReference = removed; | ||
|
|
||
| if (RemoveRecursiveJoin(node.SecondTableReference, out removed)) | ||
| node.SecondTableReference = removed; | ||
| } | ||
|
|
||
| public override void Visit(UnqualifiedJoin node) | ||
| { | ||
| base.Visit(node); | ||
|
|
||
| if (RemoveRecursiveJoin(node.FirstTableReference, out var removed)) | ||
| node.FirstTableReference = removed; | ||
| } | ||
|
|
||
| public override void ExplicitVisit(UnqualifiedJoin node) | ||
| { | ||
| node.FirstTableReference.Accept(this); | ||
|
|
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| _inUnqualifiedJoin++; | ||
|
|
||
| if (RemoveRecursiveJoin(node.SecondTableReference, out var removed)) | ||
| node.SecondTableReference = removed; | ||
|
|
||
| node.SecondTableReference.Accept(this); | ||
| _inUnqualifiedJoin--; | ||
| } | ||
|
|
||
| public override void ExplicitVisit(QuerySpecification node) | ||
| { | ||
| base.ExplicitVisit(node); | ||
|
|
||
| if (_joinPredicate != null) | ||
| { | ||
| if (node.WhereClause == null) | ||
| { | ||
| node.WhereClause = new WhereClause { SearchCondition = _joinPredicate }; | ||
| } | ||
| else | ||
| { | ||
| node.WhereClause.SearchCondition = new BooleanBinaryExpression | ||
| { | ||
| FirstExpression = node.WhereClause.SearchCondition, | ||
| BinaryExpressionType = BooleanBinaryExpressionType.And, | ||
| SecondExpression = _joinPredicate | ||
| }; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |