How to Handle JSON Data with Mixed Single and Array Values for the Same Property?

JSON data

Question:

When processing JSON data, the same attribute can often be expressed as a single value, or it can be represented as a value array. For example, the following valid loads obtained from Sendgrid API:

"Category" attribute illustrates this problem. For certain projects, it is a string, and for other items, it is a string array. JSON.NET provides two methods to deal with this inconsistency: modify the transmitted data or configure json.net to accept differences.

<code class="language-json">[
  {
    "email": "[email protected]",
    "timestamp": 1337966815,
    "category": [
      "newuser",
      "transactional"
    ],
    "event": "open"
  },
  {
    "email": "[email protected]",
    "timestamp": 1337966815,
    "category": "olduser",
    "event": "open"
  }
]</code>

Solution: Jsonconveter

The recommended method is to use custom JSONCONVERRER. Let us define a class to retrofit data:

For the attributes that may be a single item or array (in this example, "Category"), we define it as list

and specify a custom converter to process its retrofit.

<code class="language-csharp">class Item
{
    [JsonProperty("email")]
    public string Email { get; set; }

    [JsonProperty("timestamp")]
    public int Timestamp { get; set; }

    [JsonProperty("event")]
    public string Event { get; set; }

    [JsonProperty("category")]
    [JsonConverter(typeof(SingleOrArrayConverter<string>))]
    public List<string> Categories { get; set; }
}</code>

The following is the implementation of the converter:

This converter determines whether the label passed into an array or a single item is processed accordingly. If it is an array, it converts it to List

; otherwise, it will pack the project in a new list.

<code class="language-csharp">class SingleOrArrayConverter<T> : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(List<T>));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JToken token = JToken.Load(reader);
        if (token.Type == JTokenType.Array)
        {
            return token.ToObject<List<T>>();
        }
        if (token.Type == JTokenType.Null)
        {
            return null;
        }
        return new List<T> { token.ToObject<T>() };
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}</code>

Usage and output

To use a custom converter, please update the derivative code as shown below:

The program will be correctly serialized JSON data, and the "Category" attribute will be appropriately filled into a string list for a single situation and array situation.

This method provides a flexible method to process JSON data with the same property with a mixed value type. It does not need to modify the data or cause potential data loss due to inconsistent processing.

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