How do I convert a dictionary to a JSON String in C#?

Question

I want to convert my Dictionary<int,List<int>> to JSON string. Does anyone know how to achieve this in C#?

Solution 1

Serializing data structures containing only numeric or boolean values is fairly straightforward. If you don't have much to serialize, you can write a method for your specific type.

For a Dictionary<int, List<int>> as you have specified, you can use Linq:

string MyDictionaryToJson(Dictionary<int, List<int>> dict)
{
    var entries = dict.Select(d =>
        string.Format("\"{0}\": [{1}]", d.Key, string.Join(",", d.Value)));
    return "{" + string.Join(",", entries) + "}";
}

But, if you are serializing several different classes, or more complex data structures, or especially if your data contains string values, you would be better off using a reputable JSON library that already knows how to handle things like escape characters and line breaks. Json.NET is a popular option.

Solution 2

This answer mentions Json.NET but stops short of telling you how you can use Json.NET to serialize a dictionary:

return JsonConvert.SerializeObject( myDictionary );

As opposed to JavaScriptSerializer, myDictionary does not have to be a dictionary of type <string, string> for JsonConvert to work.

Solution 3

Json.NET probably serializes C# dictionaries adequately now, but when the OP originally posted this question, many MVC developers may have been using the JavaScriptSerializer class because that was the default option out of the box.

If you're working on a legacy project (MVC 1 or MVC 2), and you can't use Json.NET, I recommend that you use a List<KeyValuePair<K,V>> instead of a Dictionary<K,V>>. The legacy JavaScriptSerializer class will serialize this type just fine, but it will have problems with a dictionary.

Documentation: Serializing Collections with Json.NET

Solution 4

Simple One-Line Answer

(using System.Web.Script.Serialization )

This code will convert any Dictionary<Key,Value> to Dictionary<string,string> and then serialize it as a JSON string:

var json = new JavaScriptSerializer().Serialize(yourDictionary.ToDictionary(item => item.Key.ToString(), item => item.Value.ToString()));

It is worthwhile to note that something like Dictionary<int, MyClass> can also be serialized in this way while preserving the complex type/object.

---

Explanation (breakdown)

var yourDictionary = new Dictionary<Key,Value>(); //This is just to represent your current Dictionary.

You can replace the variable yourDictionary with your actual variable.

var convertedDictionary = yourDictionary.ToDictionary(item => item.Key.ToString(), item => item.Value.ToString()); //This converts your dictionary to have the Key and Value of type string.

We do this, because both the Key and Value has to be of type string, as a requirement for serialization of a Dictionary.

var json = new JavaScriptSerializer().Serialize(convertedDictionary); //You can then serialize the Dictionary, as both the Key and Value is of type string, which is required for serialization.

Solution 5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.Serialization.Json;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<int, List<int>> foo = new Dictionary<int, List<int>>();

            foo.Add(1, new List<int>( new int[] { 1, 2, 3, 4 }));
            foo.Add(2, new List<int>(new int[] { 2, 3, 4, 1 }));
            foo.Add(3, new List<int>(new int[] { 3, 4, 1, 2 }));
            foo.Add(4, new List<int>(new int[] { 4, 1, 2, 3 }));

            DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(Dictionary<int, List<int>>));

            using (MemoryStream ms = new MemoryStream())
            {
                serializer.WriteObject(ms, foo);
                Console.WriteLine(Encoding.Default.GetString(ms.ToArray()));
            }
        }
    }
}

This will write to the console:

[{\"Key\":1,\"Value\":[1,2,3,4]},{\"Key\":2,\"Value\":[2,3,4,1]},{\"Key\":3,\"Value\":[3,4,1,2]},{\"Key\":4,\"Value\":[4,1,2,3]}]

View more solutions

Comments

[RayLoveless]

Use newtonSoft.json nuget package. JsonConvert.SerializeObject(yourObject)

[TheDOSandDONTS]

are dictionaries serializeable?

[Twelve47]

I would have thought this would work - string json = serializer.Serialize((object)dict);

[daehaai]

I think this works better in my case as its is simple. All I need to do now is to use JSON.parse() (in javascript) in my javascript and I have my data struct ready . thx

[Pavel Chuchuva]

It throws ArgumentException: Type 'System.Collections.Generic.Dictionary`2 is not supported for serialization/deserialization of a dictionary, keys must be strings or objects.

[Pavel Chuchuva]

See stackoverflow.com/questions/3685732/…

[jacobsimeon]

This solution is naive at best. Use a real json serialization library.

[gilly3]

@Jacob - Naive? Ouch. Personally, I can't justify including another assembly when all I need to do can be accomplished with one short and simple method.

[Gomes]

Perfect answer for asp.net mvc3 and mvc4 users

[Léon Pelletier]

One more + on gilly3 comment. Sometime you're coding on Windows Phone. You're adding zlip, twitter, google, audio processing stuff, image processing stuff. You're better implement simple method like it, and some basic HttpRequests for social media interaction if your usage is simple. When adding an assembly, you always have to deal with bugs, and with the impossibility of getting a lite version. By the way, inside json libs, there are naive methods like this and no magic.

[Léon Pelletier]

There should be a page on every open project telling you: "Hey, most of the time, you'll only want to execute this 10 lines algo. Here's the code."

[EternalWulf]

@Numenor Yes, they are, but only if the Key AND Value are of type string. I have posted an answer here that includes that, if you want to have a look.

[Sleeper Smith]

dict.add("RandomKey\"", "RandomValue\""); BOOOOOOOOOOOOOOOOM. Naive at best. Use a real json serialization library.

[Jonny]

What's a LINQ? There is nothing that doesn't require foreign library?

[Jonny]

I don't have JavaScriptSerializer in my C#.

[gilly3]

@jonny - LINQ is built in to .Net. It is not a foreign library.

[James Newton-King]

This is not a good answer for dictionaries with string keys or values. Double quotes, slashes and line breaks will all result in broken JSON. It should be updated to include a warning.

[gilly3]

@JamesNewton-King - Done. Funny, I was legitimately confused by Jacob's comment, and its accompanying upvotes. I was baffled again by Sleeper's comment, but it at least got me thinking. It never even occurred to me that readers were considering my method for serializing strings. "Of course this is a bad approach for strings", I thought, "that's obvious." I now understand the haters. This question probably ranks highly in search results for serializing dictionaries, but my answer isn't a great general purpose answer for serializing any IDictionary<TKey, TValue>. Sorry to have been so blind!

[Gyum Fox]

@HowlinWulf to be more exact, the value doesn't have to be a string. But for the key, it cannot definitely be an int. Strings work best as key.

[StingyJack]

JsonConvert.SerializeObject does not appear to handle serializing c# dictionaries to a type of enumerable collection when read back into Javascript. Rather, it makes an object where each pair in the C# collection is now a plain property/value in an object, that cant be easily enumerated like a collection. So, unless I have a bad version from nuget, Json.NET is still not adequate.in this regard.

[StingyJack]

Oh, yes. I was doing a similar thing already, but trying to find out another way, and stumbled upon this. I felt it may be useful to let others know to avoid the Json.NET rabbit hole for this item (works great otherwise).

[aminhotob]

@Jonny you are missing reference assembly System.Web.Extensions msdn.microsoft.com/en-us/library/…

[vapcguy]

I referenced System.Core and then tried to reference using Newtonsoft.Json and no joy. I think Newtonsoft is a 3rd-party library.

[vapcguy]

I've read that System.Web.Extensions is not in the Client Framework version, but requires the full version, too.

[Skorunka František]

@vapcguy Yes, Newtonsoft is 3rd-party but widely used and adopted also by MS in their products. nuget.org/packages/Newtonsoft.Json

[vapcguy]

@Twelve47 Should include a sample usage, in case that link is ever moved. Otherwise this answer could become useless, one day.

[Suncat2000]

Could be a solution for limited applications, but forcing all values to type string won't yield the correct JSON if any object properties are not type string.

[Andrew]

This is a good solution if you're not dealing with complicated data structures. It avoids adding any special libraries.

[Michael Freidgeim]

It is useful for serializing of collection objects similar to key/value, such as ClaimsPrincipal.Claims

[Bernardo Dal Corno]

If you dont convert it works as well. Value can be another dictionary just like json

[T.Todua]

best answer on this topic.

[Naga]

This did not work for me this code has produced json {"abc,1": [xyz], "abc,2": [lmn]...when tested this json in online json formatter gave me error I think better to use library for stable solution

[Max]

Agreed, this is not an appropriate answer as it will not generate valid JSON in all cases

[Christos Lytras]

We can combine this with Dictionary<string, dynamic> and have all JSON primitive types like intergers, floats, booleans, strings, even nulls and within one object. +1

[GunWanderer]

This should be the answer.

[Mali Tbt]

I have a dictionary result = new Dictionary<string, object>(); and when serialize itr JsonConvert.SerializeObject(result), it converts number from 1 to 1.0 . Any idea how to avoid it?

[James Westgate]

The OP asked about integer values. Is this narrowly defined scope, this is still a valuable answer.