Question 225175 in Json Question posted in
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Json – Deserialize field with array or string

in my .NET 5 application I deserialize data using the System.Text.Json functions. This works for the most part.
Except for one field in the received JSON document, which can contain a number array, a string array or a single string (without array).

I can handle the first two cases by defining the field in my target type as List<dynamic>. But if the third case occurs, the standalone string, an exception is thrown.

How can I achieve that this third case is also handled without exception. I would prefer to get a single element in my list. Is this possible?

This are 3 possible values in JSON:

{
  "range": [
    0,
    100
  ]
}

{
  "range": [
    "yes",
    "no"
  ]
}

{
  "range": "n/a"
}
Tags:

2

Answers


  1. 0

    You will need either to write custom converter or dive into dynamic deserialization for example with JsonDocument:

    // .NET 7 feature here - raw string literals:
var jsons = new[]
{
    """
    {
      "range": [
        0,
        100
      ]
    }
    """,
    """
    {
      "range": [
        "yes",
        "no"
      ]
    }
    """,
    """
    {
      "range": "n/a"
    }
    """
};

foreach (var jsonStr in jsons)
{
    using var jd = JsonDocument.Parse(jsonStr);
    var jsonElement = jd.RootElement.GetProperty("range");
    switch (jsonElement.ValueKind)
    {
        case JsonValueKind.Array:
            var array = jsonElement.Deserialize<object[]>();
            Console.WriteLine(array.Length);
            break;
        case JsonValueKind.String:
            Console.WriteLine(jsonElement.GetString());
            break;
    }
}

    Demo @sharplab.io

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  2. 0

    you can try this custom converter

    var testRange = System.Text.Json.JsonSerializer.Deserialize<TestRange>(json);

public class TestRange
{
    [System.Text.Json.Serialization.JsonConverter(typeof(ToListJsonConverter))]
    public List<object>? range { get; set; }
}

public class ToListJsonConverter : System.Text.Json.Serialization.JsonConverter<List<object>>
{
    public override List<object> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.StartArray)
        {
            var arr = System.Text.Json.JsonSerializer.Deserialize<List<object>>(ref reader, options);
            if (arr is null) return default;
                  else  return  arr;
        }
        else if (reader.TokenType == JsonTokenType.String) return new List<object> { reader.GetString() };
        return default;
    }

    public override void Write(Utf8JsonWriter writer, List<object> value, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
}
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