Cosmos DB - CreateDocumentQuery 不反序列化抽象类型答案

【问题标题】：Cosmos DB - CreateDocumentQuery not Deserializing Abstract TypeCosmos DB - CreateDocumentQuery 不反序列化抽象类型
【发布时间】：2018-01-16 06:22:33
【问题描述】：

我正在尝试让 Cosmos DB .NET SDK v1.19.1 使用 Json.net 序列化设置自动将对象反序列化为正确的类型。除了查询文档时，这似乎工作正常。以如下代码为例：

    public abstract class Shape
    {
        public int Area { get; set; }
    }

    public class Square : Shape { }
    public class Triangle : Shape { }

    public class Entity
    {
        public string Id { get; set; }
        public string Name { get; set; }
        public Shape Shape { get; set; }
    }

    static void Main(string[] args)
    {
        JsonConvert.DefaultSettings = () => new JsonSerializerSettings()
        {
            ContractResolver = new CamelCasePropertyNamesContractResolver(),
            TypeNameHandling = TypeNameHandling.Auto
        };
        var database = "db";
        var collection = "coll";
        var client = new DocumentClient(new Uri("https://docdburi.documents.azure.com:443/"), "supersecretkey", JsonConvert.DefaultSettings());

        var entity = new Entity() { Id = "testid", Name = "John Doe", Shape = new Square() { Area = 5 } };
        var doc = client.CreateDocumentAsync(UriFactory.CreateDocumentCollectionUri(database, collection), entity).Result;
        entity = client.ReadDocumentAsync<Entity>(UriFactory.CreateDocumentUri(database, collection, entity.Id)).Result;

        // all good so far ... next line throws serialization exception on abstract shape type
        var result = client.CreateDocumentQuery<Entity>(UriFactory.CreateDocumentCollectionUri(database, collection), new FeedOptions() { MaxItemCount = 1 })
            .Where(x => x.Id == entity.Id).AsDocumentQuery()
            .ExecuteNextAsync<Entity>().Result;

文档在 Cosmos DB 中创建，形状上的 $type 属性符合预期，并且检索文档工作正常。只有当我尝试查询引发异常的文档时。关于如何让它发挥作用的任何想法？

关于如何最好地处理抽象类型还有其他建议吗？我有一个包含多层抽象类型的相当深的对象图。

【问题讨论】：

标签： c# json azure-cosmosdb

【解决方案1】：

这个助手通常对我有用：

public abstract class SerializableObject<T>
{    
    public static T FromJObject(JObject jObject) => 
         Parse($"{jObject}");

    public static T Parse(string json) =>
        JsonConvert.DeserializeObject<T>(json, 
            new JsonSerializerSettings
            {
                TypeNameHandling = TypeNameHandling.Objects
            });

    public JObject ToJObject() => JObject.Parse(ToJson());

    public string ToJson() =>
        JsonConvert.SerializeObject(this, Formatting.Indented, 
            new JsonSerializerSettings
            {
                TypeNameHandling = TypeNameHandling.Objects
            });
}

现在继承你的 Entity 类：

public class Entity : SerializableObject<Entity>
{
    public string Id { get; set; }
    public string Name { get; set; }
    public Shape Shape { get; set; }
}

并尝试使用JObject 以某种方式查询它：

var result = client.CreateDocumentQuery<JObject>(
    UriFactory.CreateDocumentCollectionUri(database, collection), 
    new FeedOptions() { MaxItemCount = 1 })
        .Where(x => x.Id == entity.Id)
        .AsEnumerable()
        .Select(Entity.FromJObject)
        .FirstOrDefault();

【讨论】：