Deserializing JSON search results into strongly typed lists (JSON.NET)

Question

I have search results in JSON and I want to deserialize it into strongly typed objects

For example:

{
    searchresult: {
        resultscount: 15,
        results: [
            {
                resultnumber: 1,
                values: [
                    {
                        key:    "bookid",
                        value:  1424
                    },
                    {
                        key:    "name",
                        value:  "C# in depth"
                    },
                ]
            }
        ]
    }
}

And I have this POCO

public class Book {
    public int BookId { get; set; }
    public string Name { get; set; }
}

I want to get a list of books. Yes, I can write my own custom deserializer for this case, but I want to use a default deserializer.

Is it possible to do something like that?

IEnumerable<Book> books = JsonConvert.DeserializeObject<IEnumerable<Book>>(json);

You're 90% there.. Just create a few intermediate classes that contain the search result data. — Jeroen Vannevel
Yes, but I will get something like List<KeyValuePair<string, object>>, but I want to get List<Book> — alexvaluyskiy

dbc dbc · Accepted Answer · 2015-02-21T15:18:28

Json.NET will not do this without any customization. You have the following approaches:

Post your classes to http://json2csharp.com/ to create a literal representation of your JSON, then use Linq to transform the result into a list of Book classes:

public class Value
{
    public string key { get; set; }
    public string value { get; set; } // Type changed from "object" to "string".
}

public class Result
{
    public int resultnumber { get; set; }
    public List<Value> values { get; set; }
}

public class Searchresult
{
    public int resultscount { get; set; }
    public List<Result> results { get; set; }
}

public class RootObject
{
    public Searchresult searchresult { get; set; }
}

And then

    var root = JsonConvert.DeserializeObject<RootObject>(json);
    var books = root.searchresult.results.Select(result => new Book { Name = result.values.Find(v => v.key == "name").value, BookId = result.values.Find(v => v.key == "bookid").value });

Create a custom JsonConverter to convert the JSON to your POCO as it is being read, for instance:

internal class BookConverter : JsonConverter
{
    public override bool CanWrite
    {
        get
        {
            return false;
        }
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Book);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var values = serializer.Deserialize<List<KeyValuePair<string, string>>>(reader);
        if (values == null)
            return existingValue;
        var book = existingValue as Book;
        if (book == null)
            book = new Book();
        // The following throws an exception on missing keys.  You could handle this differently if you prefer.
        book.BookId = values.Find(v => v.Key == "bookid").Value;
        book.Name = values.Find(v => v.Key == "name").Value;
        return book;
    }

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

public class Result
{
    public int resultnumber { get; set; }

    [JsonProperty("values")] 
    [JsonConverter(typeof(BookConverter))]
    public Book Book { get; set; }
}

public class Searchresult
{
    public int resultscount { get; set; }
    public List<Result> results { get; set; }
}

public class RootObject
{
    public Searchresult searchresult { get; set; }
}

and then

    var root = JsonConvert.DeserializeObject<RootObject>(json);
    var books = root.searchresult.results.Select(result => result.Book);

Here I only implemented ReadJson as your question only asks about deserialization . You could implement WriteJson similarly if required.

Use Linq to JSON to load the JSON into a structured hierarchy of JObject's then convert the result to Book's with Linq:

    var books = 
        JObject.Parse(json).Descendants()
            .OfType<JProperty>()
            .Where(p => p.Name == "values")
            .Select(p => p.Value.ToObject<List<KeyValuePair<string, string>>>())
            .Select(values => new Book { Name = values.Find(v => v.Key == "name").Value, BookId = values.Find(v => v.Key == "bookid").Value })
            .ToList();

Deserializing JSON search results into strongly typed lists (JSON.NET)

1 Answers