Deserialize json on different classes

Question

I have a json with different kind of blocks in it. There are simple block, like text, there's no problems in deserializing them, so I won't cover them up. The problems are with three kind of blocks: media, list and quiz:

{
  "blocks": [
    {
      "type": "text",
      "data": {
           "text": "my awesome text",
           "text_truncated": "<<<same>>>"
        },
      "cover": false,
      "anchor": ""
    },
    {
      "type": "media",
      "data": {
        "items": [
          {
            "title": "title1",
            "author": "author1",
            "image": {
              "type": "image",
              "data": {
                "uuid": "eb19f678-3c9f-58f0-90c2-33bcb8237b17",
                "width": 1024,
                "height": 756,
                "size": 448952,
                "type": "jpg",
                "color": "d3c58f",
                "hash": "",
                "external_service": []
              }
            }
          },
          {
            "title": "title2",
            "author": "author2",
            "image": {
              "type": "image",
              "data": {
                "uuid": "9274038e-1e9b-5cab-9db5-4936ce88a5c9",
                "width": 750,
                "height": 563,
                "size": 164261,
                "type": "jpg",
                "color": "b7a58d",
                "hash": "",
                "external_service": []
              }
            }
          }
        ],
        "with_background": false,
        "with_border": false
      },
      "cover": false,
      "anchor": ""
    },
    {
      "type": "list",
      "data": {
        "items": [
          "foo",
          "bar"
        ],
        "type": "UL"
      },
      "cover": false,
      "anchor": ""
    },
    {
      "type": "quiz",
      "data": {
        "uid": "00bde249ff735f481620328765695",
        "hash": "29d6bf8fec36eee3",
        "tmp_hash": "",
        "title": "When?",
        "items": {
          "a16203287650": "Ashita",
          "a16203287651": "Kinou",
          "a16203287742": "Ima"
        },
        "is_public": false,
        "date_created": 1620328765
      },
      "cover": false,
      "anchor": ""
    }
  ]
}

These blocks's items property is different from one to another.

For serializing/deserializing I'm using System.Text.Json, built in net5.0. While I can deserialize this json's items into JsonElement and work with it further, I'd like to deserialize them to exact classes automatically, when I call JsonSerializer.Deserialize(...); e.g. IEnumerable<MediaBlockData>, IEnumerable<string> and so on, depending on what type (I mean json's property) it is.

While looking for answer I found out an article on mircosoft website, but I'm not wholly understand on how to implement it for my case:

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to?pivots=dotnet-5-0

Update 1

My blocks implementation:

    public class Block
    {
        [JsonPropertyName("type")]
        public string Type { get; set; }

        [JsonPropertyName("data")]
        public JsonElement Data { get; set; }

        public IBlockData ParsedData { get; set; }

        [JsonPropertyName("cover")]
        public bool Cover { get; set; }

        [JsonPropertyName("anchor")]
        public string Anchor { get; set; }

        private Type GetBlockDataType() => Type switch
        {
            "audio" => typeof(AudioBlockData),
            "code" => typeof(CodeBlockData),
            "delimiter" => typeof(DelimiterBlockData),
            "header" => typeof(HeaderBlockData),
            "image" => typeof(ImageBlockData),
            "incut" => typeof(IncutBlockData),
            "instagram" => typeof(InstagramBlockData),
            "link" => typeof(LinkBlockData),
            "list" => typeof(ListBlockData),
            "media" => typeof(MediaBlockData),
            "number" => typeof(NumberBlockData),
            "person" => typeof(PersonBlockData),
            "quiz" => typeof(QuizBlockData),
            "quote" => typeof(QuoteBlockData),
            "spotify" => typeof(SpotifyBlockData),
            "telegram" => typeof(TelegramBlockData),
            "text" => typeof(TextBlockData),
            "tiktok" => typeof(TikTokBlockData),
            "tweet" => typeof(TweetBlockData),
            "universalbox" => typeof(UniversalBoxBlockData),
            "video" => typeof(VideoBlockData),
            "yamusic" => typeof(YaMusicBlockData),
            _ => typeof(object)
        };

        public IBlockData GetBlockData()
        {
            var blockType = GetBlockDataType();

            return (IBlockData)JsonSerializer.Deserialize(Data.ToString(), blockType);
        }
    }
    
    public class ListBlockData : IBlockData
    {
        [JsonPropertyName("items")]
        public IEnumerable<string> Items { get; set; }

        [JsonPropertyName("type")]
        public string Type { get; set; }
    }
    
    public class QuizBlockData : IBlockData
    {
        [JsonPropertyName("uid")]
        public string Uid { get; set; }

        [JsonPropertyName("hash")]
        public string Hash { get; set; }

        [JsonPropertyName("tmp_hash")]
        public string TempHash { get; set; }

        [JsonPropertyName("title")]
        public string Title { get; set; }

        [JsonPropertyName("items")]
        public JsonElement Items { get; set; }

        [JsonPropertyName("is_public")]
        public bool IsPublic { get; set; }

        [JsonPropertyName("date_created")]
        public long DateCreated { get; set; }
    }
    
    public class MediaBlockData : IBlockData
    {
        [JsonPropertyName("items")]
        public IEnumerable<MediaItem> Items { get; set; }

        [JsonPropertyName("with_background")]
        public bool WithBackground { get; set; }

        [JsonPropertyName("with_border")]
        public bool WithBorder { get; set; }
    }

    public class MediaItem : Block
    {
        [JsonPropertyName("title")]
        public string Title { get; set; }

        [JsonPropertyName("author")]
        public string Author { get; set; }

        [JsonPropertyName("image")]
        public Block Image { get; set; }
    }

Update 2

Here's minimal reproducable code sample with json string in it:

using System;
using System.Collections.Generic;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace ConsoleApp1
{
    public interface IBlockData
    {

    }

    public class TextBlockData : IBlockData
    {
        [JsonPropertyName("text")]
        public string Text { get; set; }

        [JsonPropertyName("text_truncated")]
        public string TextTruncated { get; set; }
    }

    public class MediaItem : Block
    {
        [JsonPropertyName("title")]
        public string Title { get; set; }

        [JsonPropertyName("author")]
        public string Author { get; set; }

        [JsonPropertyName("image")]
        public Block Image { get; set; }
    }

    public class QuizBlockData : IBlockData
    {
        [JsonPropertyName("uid")]
        public string Uid { get; set; }

        [JsonPropertyName("hash")]
        public string Hash { get; set; }

        [JsonPropertyName("tmp_hash")]
        public string TempHash { get; set; }

        [JsonPropertyName("title")]
        public string Title { get; set; }

        [JsonPropertyName("items")]
        public JsonElement Items { get; set; } // TODO: normal class instead of JsonElement

        [JsonPropertyName("is_public")]
        public bool IsPublic { get; set; }

        [JsonPropertyName("date_created")]
        public long DateCreated { get; set; }
    }

    public class MediaBlockData : IBlockData
    {
        [JsonPropertyName("items")]
        public IEnumerable<MediaItem> Items { get; set; }

        [JsonPropertyName("with_background")]
        public bool WithBackground { get; set; }

        [JsonPropertyName("with_border")]
        public bool WithBorder { get; set; }
    }

    public class ListBlockData : IBlockData
    {
        [JsonPropertyName("items")]
        public IEnumerable<string> Items { get; set; }

        [JsonPropertyName("type")]
        public string Type { get; set; }
    }

    public class ImageBlockData : IBlockData
    {
        [JsonPropertyName("uuid")]
        public Guid Uuid { get; set; }

        [JsonPropertyName("width")]
        public int Width { get; set; }

        [JsonPropertyName("height")]
        public int Height { get; set; }

        [JsonPropertyName("size")]
        public long Size { get; set; }

        [JsonPropertyName("type")]
        public string Type { get; set; }

        [JsonPropertyName("color")]
        public string Color { get; set; }

        [JsonPropertyName("hash")]
        public string Hash { get; set; }

        [JsonPropertyName("external_service")]
        public IEnumerable<ExternalService> ExternalService { get; set; }
    }

    public class ExternalService
    {
        [JsonPropertyName("name")]
        public string Name { get; set; }

        [JsonPropertyName("id")]
        public string Id { get; set; }
    }

    public class Block
    {
        [JsonPropertyName("type")]
        public string Type { get; set; }

        [JsonPropertyName("data")]
        public JsonElement Data { get; set; }

        public IBlockData ParsedData { get; set; }

        [JsonPropertyName("cover")]
        public bool Cover { get; set; }

        [JsonPropertyName("anchor")]
        public string Anchor { get; set; }

        private Type GetBlockDataType() => Type switch
        {
            "image" => typeof(ImageBlockData),
            "list" => typeof(ListBlockData),
            "media" => typeof(MediaBlockData),
            "quiz" => typeof(QuizBlockData),
            "text" => typeof(TextBlockData),
            _ => typeof(object)
        };

        public IBlockData GetBlockData()
        {
            var blockType = GetBlockDataType();

            return (IBlockData)JsonSerializer.Deserialize(Data.ToString(), blockType);
        }
    }

    public class Root
    {
        [JsonPropertyName("blocks")]
        public IEnumerable<Block> Blocks { get; set; }
    }

    internal static class Program
    {
        private static void Main()
        {
            var json = "{\"blocks\":[{\"type\":\"text\",\"data\":{\"text\":\"my awesome text\",\"text_truncated\":\"<<<same>>>\"},\"cover\":false,\"anchor\":\"\"},{\"type\":\"media\",\"data\":{\"items\":[{\"title\":\"title1\",\"author\":\"author1\",\"image\":{\"type\":\"image\",\"data\":{\"uuid\":\"eb19f678-3c9f-58f0-90c2-33bcb8237b17\",\"width\":1024,\"height\":756,\"size\":448952,\"type\":\"jpg\",\"color\":\"d3c58f\",\"hash\":\"\",\"external_service\":[]}}},{\"title\":\"title2\",\"author\":\"author2\",\"image\":{\"type\":\"image\",\"data\":{\"uuid\":\"9274038e-1e9b-5cab-9db5-4936ce88a5c9\",\"width\":750,\"height\":563,\"size\":164261,\"type\":\"jpg\",\"color\":\"b7a58d\",\"hash\":\"\",\"external_service\":[]}}}],\"with_background\":false,\"with_border\":false},\"cover\":false,\"anchor\":\"\"},{\"type\":\"list\",\"data\":{\"items\":[\"foo\",\"bar\"],\"type\":\"UL\"},\"cover\":false,\"anchor\":\"\"},{\"type\":\"quiz\",\"data\":{\"uid\":\"00bde249ff735f481620328765695\",\"hash\":\"29d6bf8fec36eee3\",\"tmp_hash\":\"\",\"title\":\"When?\",\"items\":{\"a16203287650\":\"Ashita\",\"a16203287651\":\"Kinou\",\"a16203287742\":\"Ima\"},\"is_public\":false,\"date_created\":1620328765},\"cover\":false,\"anchor\":\"\"}]}";

            var root = JsonSerializer.Deserialize<Root>(json);

            // Example on how it can be deserialized afterwards
            foreach (Block block in root.Blocks)
            {
                block.ParsedData = block.GetBlockData();
            }
        }
    }
}

Update 3

I've been able to deserialize blocks correctly (hope there are no major issues with this code), thanks to @dbc and this post:

Deserialize JSON array which has mixed values System.Text.JSON

Updated code:

using System;
using System.Collections.Generic;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace ConsoleApp1
{
    public class BlockData
    {

    }

    public class TextBlockData : BlockData
    {
        [JsonPropertyName("text")]
        public string Text { get; set; }

        [JsonPropertyName("text_truncated")]
        public string TextTruncated { get; set; }
    }

    public class MediaItemBlock : Block
    {
        [JsonPropertyName("title")]
        public string Title { get; set; }

        [JsonPropertyName("author")]
        public string Author { get; set; }

        [JsonPropertyName("image")]
        public Block Image { get; set; }
    }

    public class QuizBlockData : BlockData
    {
        [JsonPropertyName("uid")]
        public string Uid { get; set; }

        [JsonPropertyName("hash")]
        public string Hash { get; set; }

        [JsonPropertyName("tmp_hash")]
        public string TempHash { get; set; }

        [JsonPropertyName("title")]
        public string Title { get; set; }

        [JsonPropertyName("items")]
        public Dictionary<string, string> Items { get; set; }

        [JsonPropertyName("is_public")]
        public bool IsPublic { get; set; }

        [JsonPropertyName("date_created")]
        public long DateCreated { get; set; }
    }

    public class MediaBlockData : BlockData
    {
        [JsonPropertyName("items")]
        public IEnumerable<MediaItemBlock> Items { get; set; }

        [JsonPropertyName("with_background")]
        public bool WithBackground { get; set; }

        [JsonPropertyName("with_border")]
        public bool WithBorder { get; set; }
    }

    public class ListBlockData : BlockData
    {
        [JsonPropertyName("items")]
        public IEnumerable<string> Items { get; set; }

        [JsonPropertyName("type")]
        public string Type { get; set; }
    }

    public class ImageBlockData : BlockData
    {
        [JsonPropertyName("uuid")]
        public Guid Uuid { get; set; }

        [JsonPropertyName("width")]
        public int Width { get; set; }

        [JsonPropertyName("height")]
        public int Height { get; set; }

        [JsonPropertyName("size")]
        public long Size { get; set; }

        [JsonPropertyName("type")]
        public string Type { get; set; }

        [JsonPropertyName("color")]
        public string Color { get; set; }

        [JsonPropertyName("hash")]
        public string Hash { get; set; }

        [JsonPropertyName("external_service")]
        public IEnumerable<ExternalService> ExternalService { get; set; }
    }

    public class ExternalService
    {
        [JsonPropertyName("name")]
        public string Name { get; set; }

        [JsonPropertyName("id")]
        public string Id { get; set; }
    }

    public class Block
    {
        [JsonPropertyName("type")]
        public string Type { get; set; }

        [JsonPropertyName("data")]
        public BlockData Data { get; set; }

        [JsonPropertyName("cover")]
        public bool Cover { get; set; }

        [JsonPropertyName("anchor")]
        public string Anchor { get; set; }

        public static Type GetBlockDataType(string type) => type switch
        {
            "image" => typeof(ImageBlockData),
            "list" => typeof(ListBlockData),
            "media" => typeof(MediaBlockData),
            "quiz" => typeof(QuizBlockData),
            "text" => typeof(TextBlockData),
            _ => typeof(object)
        };
    }

    public class Root
    {
        [JsonPropertyName("blocks")]
        public IEnumerable<Block> Blocks { get; set; }
    }

    internal static class Program
    {
        private static void Main()
        {
            var json = "{\"blocks\":[{\"type\":\"text\",\"data\":{\"text\":\"my awesome text\",\"text_truncated\":\"<<<same>>>\"},\"cover\":false,\"anchor\":\"\"},{\"type\":\"media\",\"data\":{\"items\":[{\"title\":\"title1\",\"author\":\"author1\",\"image\":{\"type\":\"image\",\"data\":{\"uuid\":\"eb19f678-3c9f-58f0-90c2-33bcb8237b17\",\"width\":1024,\"height\":756,\"size\":448952,\"type\":\"jpg\",\"color\":\"d3c58f\",\"hash\":\"\",\"external_service\":[]}}},{\"title\":\"title2\",\"author\":\"author2\",\"image\":{\"type\":\"image\",\"data\":{\"uuid\":\"9274038e-1e9b-5cab-9db5-4936ce88a5c9\",\"width\":750,\"height\":563,\"size\":164261,\"type\":\"jpg\",\"color\":\"b7a58d\",\"hash\":\"\",\"external_service\":[]}}}],\"with_background\":false,\"with_border\":false},\"cover\":false,\"anchor\":\"\"},{\"type\":\"list\",\"data\":{\"items\":[\"foo\",\"bar\"],\"type\":\"UL\"},\"cover\":false,\"anchor\":\"\"},{\"type\":\"quiz\",\"data\":{\"uid\":\"00bde249ff735f481620328765695\",\"hash\":\"29d6bf8fec36eee3\",\"tmp_hash\":\"\",\"title\":\"When?\",\"items\":{\"a16203287650\":\"Ashita\",\"a16203287651\":\"Kinou\",\"a16203287742\":\"Ima\"},\"is_public\":false,\"date_created\":1620328765},\"cover\":false,\"anchor\":\"\"}]}";

            var options = new JsonSerializerOptions
            {
                Converters = { new BlockConverter() }
            };

            var root = JsonSerializer.Deserialize<Root>(json, options);
            var ser = JsonSerializer.Serialize(root, options);
        }
    }

    public class BlockConverter : JsonConverter<Block>
    {
        public override Block Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
        {
            using JsonDocument doc = JsonDocument.ParseValue(ref reader);

            // Get type for convert
            string type = doc.RootElement.GetProperty("type").GetString();

            // Create new block with default deserializer
            Block block = JsonSerializer.Deserialize<Block>(doc.RootElement.GetRawText());

            // Warning: recursive for types with blocks inside
            block.Data = (BlockData)JsonSerializer.Deserialize(doc.RootElement.GetProperty("data").GetRawText(),
                                                               Block.GetBlockDataType(type), options);

            return block;
        }

        public override void Write(Utf8JsonWriter writer, Block value, JsonSerializerOptions options)
        {
            throw new NotImplementedException();
        }
    }
}

Now I'm trying to serialize it back to string correctly, not yet happening.

Can you also add the class structure and code you are using in the code? You shouldn't need a custom converter for this as object deserialisation is supported by the .Net5 library. — blockingHD, May 07 '21 at 12:55
@blockingHD sure! I've updated the question with code snippet. — Gigas002, May 07 '21 at 13:06
Looks like you have a polymorphic type hierarchy. Serialization of such hierarchies is not supported out of the box by `System.Text.Json`. You will need to write a custom converter to do that. To do so, see [Is polymorphic deserialization possible in System.Text.Json?](https://stackoverflow.com/q/58074304/3744182). Does that answer your question, or do you need additional help? — dbc, May 07 '21 at 13:16
@dbc thank you for your answer! I've seen similar example on microsoft guilde to json converters for `System.Text.Json`, but I honestly don't quite understand on how to implement it for my case. — Gigas002, May 07 '21 at 13:31
Then can you strip your code down into a [mcve]? The code you have shared so far does not even compile, see https://dotnetfiddle.net/8UT9r4. Without a complete, compilable example, all we can do is point you to [Is polymorphic deserialization possible in System.Text.Json?](https://stackoverflow.com/q/58074304/3744182) — dbc, May 07 '21 at 13:40
@dbc I've updated the question with minimal reproducable code sample with json from this question included. — Gigas002, May 07 '21 at 14:07
@dbc I've managed to deserialize json correctly, thanks for your help! Now I'm stuck at serializing it back to string though — Gigas002, May 07 '21 at 19:36

score 1 · Answer 1 · answered May 10 '21 at 02:41

Here's a version that desieralises this json without using a converter.

var media = new List<MediaBlock>();
var texts = new List<TextBlock>();

using var doc = JsonDocument.Parse(json);
foreach (var block in doc.RootElement.GetProperty("blocks").EnumerateArray())
{
    switch (block.GetProperty("type").GetString())
    {
        case "text": texts.Add(Deserialise<TextBlock>(block.GetProperty("data"))); break;
        case "media": media.Add(Deserialise<MediaBlock>(block.GetProperty("data"))); break;
        // ... 
    }
}

var composite = new 
{
    Texts = texts,// compsite.Texts[0].Text is 'my awesome text'
    Media = media // compsite.Media.Items[0].Author is 'author1'
};

// This is OK, but if you need speed, please have a look at
// https://stackoverflow.com/questions/58138793/system-text-json-jsonelement-toobject-workaround
static T Deserialise<T>(JsonElement e) => JsonSerializer.Deserialize<T>(e.GetRawText(), options: new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

The auxiliary classes I used are:

class MediaBlock
{
    public List<MediaItem> Items { get; set; }
}

class MediaItem
{
    public string Author { get; set; }
    public string Title { get; set; }
    // ...
}

class TextBlock
{
    public string Text { get; set; }
}

Interesting approach, thanks for additional info! – Gigas002 May 10 '21 at 17:18 — Gigas002, May 10 '21 at 17:18

Deserialize json on different classes

1 Answers1