System.Text.Json 和动态解析多态对象

Question

我不相信我正在考虑如何在解析 json 结果时正确使用 JsonConverter 进行多态性。

在我的场景中，我的目标是 TFS 中的 Git 策略配置。策略配置：

"value": [
{
        "createdBy": {
            "displayName": "username",
            "url": "url",
            "id": "id",
            "uniqueName": "user",
            "imageUrl": "url"
        },
        "createdDate": "2020-03-21T18:17:24.3240783Z",
        "isEnabled": true,
        "isBlocking": true,
        "isDeleted": false,
        "settings": {
            "minimumApproverCount": 1,
            "creatorVoteCounts": false,
            "allowDownvotes": false,
            "resetOnSourcePush": true,
            "scope": [{
                    "refName": "refs/heads/master",
                    "matchKind": "Exact",
                    "repositoryId": "id"
                }
            ]
        },
        "_links": {
            "self": {
                "href": "url"
            },
            "policyType": {
                "href": "url"
            }
        },
        "revision": 1,
        "id": 974,
        "url": "url",
        "type": {
            "id": "id",
            "url": "url",
            "displayName": "Minimum number of reviewers"
        },
{...}]

更多settings示例：需要合并策略

"settings": {
        "useSquashMerge": true,
        "scope": [
            {
                "refName": "refs/heads/master",
                "matchKind": "Exact",
                "repositoryId": "id"
            }
        ]
    }

所需的审稿人

    "settings": {
        "requiredReviewerIds": [
            "id"
        ],
        "scope": [
            {
                "refName": "refs/heads/master",
                "matchKind": "Exact",
                "repositoryId": "id"
            }
        ]
    }

在上面的 json 片段中，设置对象因配置类型而异。

与可以动态序列化/反序列化设置对象相比，编写转换器的最佳方法是什么？我已经阅读了几篇关于此的文章，但无法完全理解它。

---

这就是我目前反序列化我所有 API 结果的方式，到目前为止它们都是简单的结果集。

async Task<List<T>> ParseResults<T>( HttpResponseMessage result, string parameter )
{
    List<T> results = new List<T>();

    if ( result.IsSuccessStatusCode )
    {
        using var stream = await result.Content.ReadAsStreamAsync();
        JsonDocument doc = JsonDocument.Parse( stream );
        JsonElement collection = doc.RootElement.GetProperty( parameter ).Clone();

        foreach ( var item in collection.EnumerateArray() )
        {
            results.Add( JsonSerializer.Deserialize<T>( item.ToString() ) );
        }
    }

    return results;
}

我的集成测试。

PolicyConfiguration 是我试图反序列化的类型。

[Test]
public async Task Get_TestMasterBranchPolicyConfigurations()
{
    HttpResponseMessage result = await GetResult( $"{_collection}/ProductionBuildTesting/_apis/policy/configurations?api-version=4.1" );

    List<PolicyConfiguration> configurations = await ParseResults<PolicyConfiguration>( result, "value" );
    Assert.AreEqual( 16, configurations.Count );
    JsonPrint( configurations );
}

我目前针对这种解析情况的课程

public class CreatedBy
{
    [JsonPropertyName( "displayName" )]
    public string DisplayName { get; set; }
    [JsonPropertyName( "url" )]
    public string Url { get; set; }
    [JsonPropertyName( "id" )]
    public Guid Id { get; set; }
    [JsonPropertyName( "uniqueName" )]
    public string UniqueName { get; set; }
    [JsonPropertyName( "imageUrl" )]
    public string ImageUrl { get; set; }
}

public class PolicyConfigurationScope
{
    [JsonPropertyName( "refName" )]
    public string RefName { get; set; }
    [JsonPropertyName( "matchKind" )]
    public string MatchKind { get; set; }
    [JsonPropertyName( "repositoryId" )]
    public Guid RepositoryId { get; set; }
}

public class PolicyConfigurationSettings_MinimumNumberOfReviewers
{
    [JsonPropertyName( "minimumApproverCount" )]
    public int MinimumApproverCount { get; set; }
    [JsonPropertyName( "creatorVoteCounts" )]
    public bool CreatorVoteCounts { get; set; }
    [JsonPropertyName( "allowDownvotes" )]
    public bool AllowDownvotes { get; set; }
    [JsonPropertyName( "resetOnSourcePush" )]
    public bool ResetOnSourcePush { get; set; }
    [JsonPropertyName( "scope" )]
    public List<PolicyConfigurationScope> Scope { get; set; }
}

public class PolicyConfigurationType
{
    [JsonPropertyName( "id" )]
    public Guid Id { get; set; }
    [JsonPropertyName( "url" )]
    public string Url { get; set; }
    [JsonPropertyName( "displayName" )]
    public string DisplayName { get; set; }
}

public class PolicyConfiguration
{
    [JsonPropertyName( "createdBy" )]
    public CreatedBy CreatedBy { get; set; }
    [JsonPropertyName( "createdDate" )]
    public DateTime CreatedDate { get; set; }
    [JsonPropertyName( "isEnabled" )]
    public bool IsEnabled { get; set; }
    [JsonPropertyName( "isBlocking" )]
    public bool IsBlocking { get; set; }
    [JsonPropertyName( "isDeleted" )]
    public bool IsDeleted { get; set; }
    //[JsonPropertyName( "settings" )]
    //public PolicyConfigurationSettings_MinimumNumberOfReviewersSettings Settings { get; set; }
    [JsonPropertyName( "revision" )]
    public int Revision { get; set; }
    [JsonPropertyName( "id" )]
    public int Id { get; set; }
    [JsonPropertyName( "url" )]
    public string Url { get; set; }
    [JsonPropertyName( "type" )]
    public PolicyConfigurationType Type { get; set; }
}

Answer 1

我最终以与之前使用鉴别器看到的文章相同的方式解决了我的问题。因为我不控制 API 提要，所以我没有可以驱散的鉴别器，所以我依赖于 Json 对象的属性。

需要创建一个转换器：

public class PolicyConfigurationSettingsConverter : JsonConverter<PolicyConfigurationSettings>
{
    public override PolicyConfigurationSettings Read( ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options )
    {
        JsonDocument doc;
        JsonDocument.TryParseValue( ref reader, out doc );

        if ( doc.RootElement.TryGetProperty( "minimumApproverCount", out _ ) )
            return JsonSerializer.Deserialize<MinimumNumberOfReviewers>( doc.RootElement.ToString(), options );
        if ( doc.RootElement.TryGetProperty( "useSquashMerge", out _ ) )
            return JsonSerializer.Deserialize<RequireAMergeStrategy>( doc.RootElement.ToString(), options );
        if ( doc.RootElement.TryGetProperty( "scope", out _ ) )
            return JsonSerializer.Deserialize<PolicyConfigurationSettingsScope>( doc.RootElement.ToString(), options );

        return null;
    }

    public override void Write( Utf8JsonWriter writer, [DisallowNull] PolicyConfigurationSettings value, JsonSerializerOptions options )
    {
        if ( value.GetType() == typeof( MinimumNumberOfReviewers ) )
            JsonSerializer.Serialize( writer, ( MinimumNumberOfReviewers )value, options );
        if ( value.GetType() == typeof( RequireAMergeStrategy ) )
            JsonSerializer.Serialize( writer, ( RequireAMergeStrategy )value, options );
        if ( value.GetType() == typeof( PolicyConfigurationSettingsScope ) )
            JsonSerializer.Serialize( writer, ( PolicyConfigurationSettingsScope )value, options );
    }
}

然后需要创建一个JsonSerializerOptions对象来添加Converter

public static JsonSerializerOptions PolicyConfigurationSettingsSerializerOptions()
{
    var serializeOptions = new JsonSerializerOptions();
    serializeOptions.Converters.Add( new PolicyConfigurationSettingsConverter() );
    return serializeOptions;
}

将选项传递到您的 Serializer/Deserializer 语句中。

下面是PolicyConfigurationSettings班级

public abstract class PolicyConfigurationSettings
{
    [JsonPropertyName( "scope" )]
    public List<PolicyConfigurationScope> Scope { get; set; }
}

public class MinimumNumberOfReviewers : PolicyConfigurationSettings
{
    [JsonPropertyName( "minimumApproverCount" )]
    public int MinimumApproverCount { get; set; }
    [JsonPropertyName( "creatorVoteCounts" )]
    public bool CreatorVoteCounts { get; set; }
    [JsonPropertyName( "allowDownvotes" )]
    public bool AllowDownvotes { get; set; }
    [JsonPropertyName( "resetOnSourcePush" )]
    public bool ResetOnSourcePush { get; set; }
}

public class RequireAMergeStrategy : PolicyConfigurationSettings
{
    [JsonPropertyName( "useSquashMerge" )]
    public bool UseSquashMerge { get; set; }
}

public class PolicyConfigurationSettingsScope : PolicyConfigurationSettings { }