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Add support for preserve references on JSON (dotnet#655)
* Initial commit for JSON reference handling / preserve references * Remove ReferenceHandling.Ignore option * Code clean-up. * Remove stale tests. * Address PR feedback * Reference handling inline (dotnet#1) * Inline ReferenceHandling logic within main methods. * remove stale Handle*Ref methods * Refactor the code for Deserialization * Create methods to reuse code * Try to isolate Preserve logic as much as I can * Replaced Exceptions for ThrowHelper methods * Remove stale condition on $ref * Add AggressiveInlining to HandlePropertyNameDefault * Inline feature code in Serialization * Fix preserve references for ExtensionData * Split Reference dictionary into two, for (De)Serialize each. Add Reference EqualityComparer to Serialize dictionary. * Do not set PropertyName to s_missingProperty to avoid race condition issues. * Remove Asserts that compare against an exception message. * Set preserved array passing setPropertyDirectly = true to avoid issue when enumerable is already initialized. * Code clean-up. * Separate write code into WritePreservedObject and WriteReferenceObject * Address some PR feedback: * Switched ReferenceResolver to access it through a read-only property that initializes it the first time is tried to be accesed. * Renamed some methods and properties * Refactored WriteReference* methods. * Fixed Exception messages * Removed literal message comparison on tests. * * Add round-tripping coverage to suitable unit tests * Fix issues found with Round-tripping scenarios * Move DictionaryPropertyIsPreserved to EndProperty() in order to fix issue where two dictionary properties were next to each other and the DictionaryPropertyIsPreserved was not reset. * Add ReadStackFrame.IsNestedPreservedArray in order to identify preserved arrays nested and prevent using setPropertyDirectly on them. * Add nullability annotations * Code clean-up, reword comments and removed unnecesary properties in ReferenceHandling * Fix issue where an object that tries to map into an enumerable could skip the validation that prevents this. * Fix issue where the wrong type was passed into the throw helper for nested enumerable in HandleStartObject * Address PR comments. * Refactor flags on ReadStackFrame to avoid using unrelated fields for validation. * Consolidated MetadataPropertyName enum logic on read and write. * Reuse HandleStartObjectInEnumerable to handle arrays with metadata nested in a Dictionary. * Refactor code: * Change ReferenceResolver from class to struct to avoid one allocation. * Replace propertyName.ToArray() for constant arrays in order to avoid allocation. * Move some exception logic to the ThrowHelper class. * * Apply optimizations: * Use PropertyCacheArray on Values property lookup. * Make Comparer static field to avoid one allocation at runtime. * Document reasoning for DefaultReferenceResolver and ReferenreEqualsEqualityComparer * Address PR comments. * Addres more PR feedback: * Add documentation to DefaultReferenceResolver public methods. * Address PR feedback. * Adderss more PR suggestions. * * Move tests to Serialization namespace. * On $values, set PropertyName on state.Current.JsonPropertyName instead.
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92 changes: 92 additions & 0 deletions
92
...libraries/System.Text.Json/src/System/Text/Json/Serialization/DefaultReferenceResolver.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,92 @@ | ||
| // Licensed to the.NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
| // See the LICENSE file in the project root for more information. | ||
|
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| using System.Collections.Generic; | ||
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| namespace System.Text.Json.Serialization | ||
| { | ||
| /// <summary> | ||
| /// The default ReferenceResolver implementation to handle duplicate object references. | ||
| /// </summary> | ||
| /// <remarks> | ||
| /// It is currently a struct to save one unnecessary allcation while (de)serializing. | ||
| /// If we choose to expose the ReferenceResolver in a future, we may need to create an abstract class/interface and change this type to become a class that inherits from that abstract class/interface. | ||
| /// </remarks> | ||
| internal struct DefaultReferenceResolver | ||
| { | ||
| private uint _referenceCount; | ||
| private readonly Dictionary<string, object>? _referenceIdToObjectMap; | ||
| private readonly Dictionary<object, string>? _objectToReferenceIdMap; | ||
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| public DefaultReferenceResolver(bool writing) | ||
| { | ||
| _referenceCount = default; | ||
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| if (writing) | ||
| { | ||
| // Comparer used here to always do a Reference Equality comparison on serialization which is where we use the objects as the TKey in our dictionary. | ||
| _objectToReferenceIdMap = new Dictionary<object, string>(ReferenceEqualsEqualityComparer<object>.Comparer); | ||
| _referenceIdToObjectMap = null; | ||
| } | ||
| else | ||
| { | ||
| _referenceIdToObjectMap = new Dictionary<string, object>(); | ||
| _objectToReferenceIdMap = null; | ||
| } | ||
| } | ||
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| /// <summary> | ||
| /// Adds an entry to the bag of references using the specified id and value. | ||
| /// This method gets called when an $id metadata property from a JSON object is read. | ||
| /// </summary> | ||
| /// <param name="referenceId">The identifier of the respective JSON object or array.</param> | ||
| /// <param name="value">The value of the respective CLR reference type object that results from parsing the JSON object.</param> | ||
| public void AddReferenceOnDeserialize(string referenceId, object value) | ||
| { | ||
| if (!JsonHelpers.TryAdd(_referenceIdToObjectMap!, referenceId, value)) | ||
| { | ||
| ThrowHelper.ThrowJsonException_MetadataDuplicateIdFound(referenceId); | ||
| } | ||
| } | ||
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| /// <summary> | ||
| /// Gets the reference id of the specified value if exists; otherwise a new id is assigned. | ||
| /// This method gets called before a CLR object is written so we can decide whether to write $id and the rest of its properties or $ref and step into the next object. | ||
| /// The first $id value will be 1. | ||
| /// </summary> | ||
| /// <param name="value">The value of the CLR reference type object to get or add an id for.</param> | ||
| /// <param name="referenceId">The id realated to the object.</param> | ||
| /// <returns></returns> | ||
| public bool TryGetOrAddReferenceOnSerialize(object value, out string referenceId) | ||
| { | ||
| if (!_objectToReferenceIdMap!.TryGetValue(value, out referenceId!)) | ||
| { | ||
| _referenceCount++; | ||
| referenceId = _referenceCount.ToString(); | ||
| _objectToReferenceIdMap.Add(value, referenceId); | ||
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| return false; | ||
| } | ||
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| return true; | ||
| } | ||
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| /// <summary> | ||
| /// Resolves the CLR reference type object related to the specified reference id. | ||
| /// This method gets called when $ref metadata property is read. | ||
| /// </summary> | ||
| /// <param name="referenceId">The id related to the returned object.</param> | ||
| /// <returns></returns> | ||
| public object ResolveReferenceOnDeserialize(string referenceId) | ||
| { | ||
| if (!_referenceIdToObjectMap!.TryGetValue(referenceId, out object? value)) | ||
| { | ||
| ThrowHelper.ThrowJsonException_MetadataReferenceNotFound(referenceId); | ||
| } | ||
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| return value; | ||
| } | ||
| } | ||
| } |
18 changes: 18 additions & 0 deletions
18
...ries/System.Text.Json/src/System/Text/Json/Serialization/JsonPreservableArrayReference.cs
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,18 @@ | ||
| // Licensed to the .NET Foundation under one or more agreements. | ||
| // The .NET Foundation licenses this file to you under the MIT license. | ||
| // See the LICENSE file in the project root for more information. | ||
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| namespace System.Text.Json | ||
| { | ||
| /// <summary> | ||
| /// JSON objects that contain metadata properties and the nested JSON array are wrapped into this class. | ||
| /// </summary> | ||
| /// <typeparam name="T">The original type of the enumerable.</typeparam> | ||
| internal class JsonPreservableArrayReference<T> | ||
| { | ||
| /// <summary> | ||
| /// The actual enumerable instance being preserved is extracted when we finish processing the JSON object on HandleEndObject. | ||
| /// </summary> | ||
| public T Values { get; set; } = default!; | ||
| } | ||
| } |
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