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Query: Lift more subqueries in the QueryOptimizer
Query models following a simple pattern of selecting from a subquery only to create a projection can often be flattened by lifting the subquery. These changes do that, which results in more efficient queries for such cases, and in the case of Relational, more compact SQL statements.
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src/EFCore/Query/ExpressionVisitors/Internal/MainFromClauseFlatteningQueryModelVisitor.cs
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| @@ -0,0 +1,101 @@ | ||
| // Copyright (c) .NET Foundation. All rights reserved. | ||
| // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. | ||
|
|
||
| using System.Collections.Generic; | ||
| using System.Linq; | ||
| using System.Linq.Expressions; | ||
| using JetBrains.Annotations; | ||
| using Microsoft.EntityFrameworkCore.Query.Internal; | ||
| using Microsoft.EntityFrameworkCore.Query.ResultOperators; | ||
| using Remotion.Linq; | ||
| using Remotion.Linq.Clauses; | ||
| using Remotion.Linq.Clauses.Expressions; | ||
| using Remotion.Linq.Clauses.ResultOperators; | ||
| using Remotion.Linq.Parsing; | ||
|
|
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| namespace Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal | ||
| { | ||
| /// <summary> | ||
| /// This API supports the Entity Framework Core infrastructure and is not intended to be used | ||
| /// directly from your code. This API may change or be removed in future releases. | ||
| /// </summary> | ||
| public class MainFromClauseFlatteningQueryModelVisitor : QueryModelVisitorBase | ||
| { | ||
| private readonly IEnumerable<IQueryAnnotation> _queryAnnotations; | ||
| private readonly SubQueryExpressionVisitor _subQueryExpressionVisitor; | ||
|
|
||
| /// <summary> | ||
| /// This API supports the Entity Framework Core infrastructure and is not intended to be used | ||
| /// directly from your code. This API may change or be removed in future releases. | ||
| /// </summary> | ||
| public MainFromClauseFlatteningQueryModelVisitor([NotNull] IEnumerable<IQueryAnnotation> queryAnnotations) | ||
| { | ||
| _queryAnnotations = queryAnnotations; | ||
| _subQueryExpressionVisitor = new SubQueryExpressionVisitor(this); | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// This API supports the Entity Framework Core infrastructure and is not intended to be used | ||
| /// directly from your code. This API may change or be removed in future releases. | ||
| /// </summary> | ||
| public override void VisitQueryModel([NotNull] QueryModel queryModel) | ||
| { | ||
| queryModel.TransformExpressions(_subQueryExpressionVisitor.Visit); | ||
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|
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| base.VisitQueryModel(queryModel); | ||
| } | ||
|
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| /// <summary> | ||
| /// This API supports the Entity Framework Core infrastructure and is not intended to be used | ||
| /// directly from your code. This API may change or be removed in future releases. | ||
| /// </summary> | ||
| public override void VisitMainFromClause([NotNull] MainFromClause fromClause, [NotNull] QueryModel queryModel) | ||
| { | ||
| if (fromClause.FromExpression is SubQueryExpression subQueryExpression) | ||
| { | ||
| var subQueryModel = subQueryExpression.QueryModel; | ||
|
|
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| if (subQueryModel.SelectClause.Selector is QuerySourceReferenceExpression | ||
| && !subQueryModel.ResultOperators.OfType<GroupResultOperator>().Any() | ||
| && !queryModel.BodyClauses.Any()) | ||
| { | ||
| queryModel.UpdateQuerySourceMapping( | ||
| queryModel.MainFromClause, | ||
| subQueryModel.SelectClause.Selector, | ||
| _queryAnnotations); | ||
|
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| queryModel.MainFromClause = subQueryModel.MainFromClause; | ||
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| foreach (var bodyClause in subQueryModel.BodyClauses) | ||
| { | ||
| queryModel.BodyClauses.Add(bodyClause); | ||
| } | ||
|
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| foreach (var resultOperator in subQueryModel.ResultOperators.Reverse()) | ||
| { | ||
| queryModel.ResultOperators.Insert(0, resultOperator); | ||
| } | ||
|
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| return; | ||
| } | ||
| } | ||
| } | ||
|
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| private class SubQueryExpressionVisitor : RelinqExpressionVisitor | ||
| { | ||
| private readonly MainFromClauseFlatteningQueryModelVisitor _queryModelVisitor; | ||
|
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| public SubQueryExpressionVisitor(MainFromClauseFlatteningQueryModelVisitor queryModelVisitor) | ||
| { | ||
| _queryModelVisitor = queryModelVisitor; | ||
| } | ||
|
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| protected override Expression VisitSubQuery(SubQueryExpression expression) | ||
| { | ||
| _queryModelVisitor.VisitQueryModel(expression.QueryModel); | ||
|
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| return expression; | ||
| } | ||
| } | ||
| } | ||
| } |
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