Question 251407 in Json Question posted in
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C# – Deserialize array of JSON objects into Dictionary

 {
   "TestObjects": [
     {"the": "goal"},
     {"is": "to"},
     {"deserialize": "this"},
     {"simple": "array"},
     {"of": "objects"},
     {"into": "a"},
     {"C#": "Dictionary"}
    ]
}

Using .NET System.Text.Json. Seeking methodology to deserialize an array of objects where each object has two strings, as shown above, into a Dictionary<string, string>.

I have seen answers that describe deserializing into Dictionary<string, string>[] whereby each object is placed in a distinct Dictionary<string, string>, and that works. E.g. Ten objects results in an array of ten dictionaries. Example below works:

public class TestClass
{
    public Dictionary<string, string>[] TestObjects { get; set; }
}

var stream = File.OpenRead(@"C:testtest.json");

TestClass result = JsonSerializer.Deserialize<TestClass>(stream);

So, referring to the above example that works, the goal is to deserialize into a C# property of the form
Dictionary<string, string> TestObjects { get; set; } as opposed to
Dictionary<string, string>[] TestObjects { get; set; }

Thank You

Tags:

3

Answers


  1. 0

    you can convert an array to a dictionary

    Dictionary<string, string> result = JsonDocument.Parse(json)
            .RootElement.GetProperty("SimpleArray").EnumerateArray()
            .ToDictionary(x => x.EnumerateObject().FirstOrDefault().Name,
                        x => x.EnumerateObject().FirstOrDefault().Value.ToString());

    But remember the dictionary shoud have the unique keys, otherwise you will get an exception

    or if you want to deserialize to a class, you will need to write a json converter

    TestClass result = System.Text.Json.JsonSerializer.Deserialize<TestClass>(json);

public class ToDictConverter : System.Text.Json.Serialization.JsonConverter<Dictionary<string, string>>
{
    public override Dictionary<string, string> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.StartArray)
        {
            var dict = new Dictionary<string, string>();
            while (reader.Read())
            {
                if (reader.TokenType == JsonTokenType.EndArray) return dict;
                if (reader.TokenType == JsonTokenType.PropertyName)
                {
                    string propName = reader.GetString();
                    if (reader.Read()) dict.Add(propName, reader.GetString());
                }
            }
        }
        return null;
    }

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

public class TestClass
{

[System.Text.Json.Serialization.JsonConverter(typeof(ToDictConverter))]
public Dictionary<string, string> SimpleArray { get; set; }

}
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  2. 0

    In order for it to deserialize as a Dictionary, it would have to be in this format:

    {
  "TestObjects": {
    "the": "goal",
    "is": "to",
    "convert": "this",
    "simple": "array",
    "of": "objects",
    "into": "a",
    "C#": "Dictionary"
  }
}

    You could, however, add another read-only property that converts the array of dictionaries into one dictionary.

    public class TestClass1
{
    public Dictionary<string, string>[] TestObjects { get; set; }

    public Dictionary<string, string> TestObjectsDict
    {
        get
        {
            return TestObjects.Select(x => x.First()).ToDictionary(x => x.Key, x => x.Value);
        }
    }
}
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  3. 0

    You could use a simple converter.

    Decorate the Property with [JsonConverter(...)]:

    public class TestClass2 {
    [JsonConverter(typeof(ObjectsToDictionaryConverter))]
    public Dictionary<string, string> TestObjects { get; set; }
}

    The custom converter reads each property and value from the array of objects and uses them as the Key and Value of a Dictionary.
    It’s assumed that all keys (Properties) have a different name.

    When the Utf8JsonReader gets to the end of the arrays, i.e., when [Utf8JsonReader].TokenType == JsonTokenType.EndArray, return the Dictionary:

    Note: there’s no real error checking here. I leave it to you, since you know what the real JSON contains.

    class ObjectsToDictionaryConverter : JsonConverter<Dictionary<string, string>> {
    public override Dictionary<string, string> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) {

        if (reader.TokenType != JsonTokenType.StartArray) {
            throw new JsonException($"Array of objects expected. Got {reader.TokenType}");
        }

        var dict = new Dictionary<string, string>();
        while (reader.Read()) {
            if (reader.TokenType == JsonTokenType.EndArray) break;

            if (reader.TokenType == JsonTokenType.StartObject) {
                reader.Read();
                string key = reader.GetString();
                reader.Read();
                string value = reader.GetString();
                dict.Add(key, value);
            }
        }
        return dict;
    }

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