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Better handling of nullable element comparers (#31672)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,164 @@ | ||
| // Licensed to the .NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
|
|
||
| namespace Microsoft.EntityFrameworkCore.ChangeTracking; | ||
|
|
||
| /// <summary> | ||
| /// A <see cref="ValueComparer{T}"/> for lists of primitive items. The list can be typed as <see cref="IEnumerable{T}"/>, | ||
| /// but can only be used with instances that implement <see cref="IList{T}"/>. | ||
| /// </summary> | ||
| /// <remarks> | ||
| /// <para> | ||
| /// This comparer should be used when the element of the comparer is typed as <see cref="object"/>. | ||
| /// </para> | ||
| /// <para> | ||
| /// See <see href="https://aka.ms/efcore-docs-value-comparers">EF Core value comparers</see> for more information and examples. | ||
| /// </para> | ||
| /// </remarks> | ||
| /// <typeparam name="TElement">The element type.</typeparam> | ||
| public sealed class ObjectListComparer<TElement> : ValueComparer<IEnumerable<TElement>> | ||
| { | ||
| /// <summary> | ||
| /// Creates a new instance of the list comparer. | ||
| /// </summary> | ||
| /// <param name="elementComparer">The comparer to use for comparing elements.</param> | ||
| public ObjectListComparer(ValueComparer elementComparer) | ||
| : base( | ||
| (a, b) => Compare(a, b, elementComparer), | ||
| o => GetHashCode(o, elementComparer), | ||
| source => Snapshot(source, elementComparer)) | ||
| { | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// This is an internal API that supports the Entity Framework Core infrastructure and not subject to | ||
| /// the same compatibility standards as public APIs. It may be changed or removed without notice in | ||
| /// any release. You should only use it directly in your code with extreme caution and knowing that | ||
| /// doing so can result in application failures when updating to a new Entity Framework Core release. | ||
| /// </summary> | ||
| [EntityFrameworkInternal] | ||
| public static bool Compare(IEnumerable<TElement>? a, IEnumerable<TElement>? b, ValueComparer elementComparer) | ||
| { | ||
| if (ReferenceEquals(a, b)) | ||
| { | ||
| return true; | ||
| } | ||
|
|
||
| if (a is null) | ||
| { | ||
| return b is null; | ||
| } | ||
|
|
||
| if (b is null) | ||
| { | ||
| return false; | ||
| } | ||
|
|
||
| if (a is IList<object?> aList && b is IList<object?> bList) | ||
| { | ||
| if (aList.Count != bList.Count) | ||
| { | ||
| return false; | ||
| } | ||
|
|
||
| for (var i = 0; i < aList.Count; i++) | ||
| { | ||
| var (el1, el2) = (aList[i], bList[i]); | ||
| if (el1 is null) | ||
| { | ||
| if (el2 is null) | ||
| { | ||
| continue; | ||
| } | ||
|
|
||
| return false; | ||
| } | ||
|
|
||
| if (el2 is null) | ||
| { | ||
| return false; | ||
| } | ||
|
|
||
| if (!elementComparer.Equals(el1, el2)) | ||
| { | ||
| return false; | ||
| } | ||
| } | ||
|
|
||
| return true; | ||
| } | ||
|
|
||
| throw new InvalidOperationException( | ||
| CoreStrings.BadListType( | ||
| (a is IList<TElement?> ? b : a).GetType().ShortDisplayName(), | ||
| typeof(ListComparer<TElement?>).ShortDisplayName(), | ||
| typeof(IList<>).MakeGenericType(elementComparer.Type).ShortDisplayName())); | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// This is an internal API that supports the Entity Framework Core infrastructure and not subject to | ||
| /// the same compatibility standards as public APIs. It may be changed or removed without notice in | ||
| /// any release. You should only use it directly in your code with extreme caution and knowing that | ||
| /// doing so can result in application failures when updating to a new Entity Framework Core release. | ||
| /// </summary> | ||
| [EntityFrameworkInternal] | ||
| public static int GetHashCode(IEnumerable<TElement> source, ValueComparer elementComparer) | ||
| { | ||
| var hash = new HashCode(); | ||
|
|
||
| foreach (var el in source) | ||
| { | ||
| hash.Add(el == null ? 0 : elementComparer.GetHashCode(el)); | ||
| } | ||
|
|
||
| return hash.ToHashCode(); | ||
| } | ||
|
|
||
| /// <summary> | ||
| /// This is an internal API that supports the Entity Framework Core infrastructure and not subject to | ||
| /// the same compatibility standards as public APIs. It may be changed or removed without notice in | ||
| /// any release. You should only use it directly in your code with extreme caution and knowing that | ||
| /// doing so can result in application failures when updating to a new Entity Framework Core release. | ||
| /// </summary> | ||
| [EntityFrameworkInternal] | ||
| public static IList<TElement> Snapshot(IEnumerable<TElement> source, ValueComparer elementComparer) | ||
| { | ||
| if (source is not IList<TElement> sourceList) | ||
| { | ||
| throw new InvalidOperationException( | ||
| CoreStrings.BadListType( | ||
| source.GetType().ShortDisplayName(), | ||
| typeof(ListComparer<TElement?>).ShortDisplayName(), | ||
| typeof(IList<>).MakeGenericType(elementComparer.Type).ShortDisplayName())); | ||
| } | ||
|
|
||
| if (sourceList.IsReadOnly) | ||
| { | ||
| var snapshot = new TElement[sourceList.Count]; | ||
|
|
||
| for (var i = 0; i < sourceList.Count; i++) | ||
| { | ||
| var instance = sourceList[i]; | ||
| if (instance != null) | ||
| { | ||
| snapshot[i] = (TElement)elementComparer.Snapshot(instance); | ||
| } | ||
| } | ||
|
|
||
| return snapshot; | ||
| } | ||
| else | ||
| { | ||
| var snapshot = (source is List<TElement> || sourceList.IsReadOnly) | ||
| ? new List<TElement>(sourceList.Count) | ||
| : (IList<TElement>)Activator.CreateInstance(source.GetType())!; | ||
|
|
||
| foreach (var e in sourceList) | ||
| { | ||
| snapshot.Add(e == null ? (TElement)(object?)null! : (TElement)elementComparer.Snapshot(e)); | ||
| } | ||
|
|
||
| return snapshot; | ||
| } | ||
| } | ||
| } |
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