Tuesday, April 19, 2016

Deserialize JSON string to C# dynamic type


This is the age of APIs in computer science. To be more specific web APIs. Don't get confused with the specific technology of .Net Web API. Any methods or resources which are exposed via URL in a structure is an API. From our apps we can call them to do achieve the functionality.

Resources are now a days exposed via ReST protocol and the format is JSON. It works well with JavaScript. But when coming to .Net world, its little difficult to keep the JSON as is in our app. Often we need to convert those resources into entity classes. Creating entity class for each API response is a tricky tasks. It puts more time to complete the API integration tasks. Often after using one API for months we may need to switch to another API providing same service. At that time we need to rewrite it. Creating classes to get exact replica of response is really difficult to manage.

But its always suggested to have entity classes which are for our application regardless of the API we are using. As soon as we got the response from the web API, we should convert the response to our model and that should go on from that point on wards.

Dynamic object to hold JSON

In the beginning people were programming without type safety. Then the strong typed languages were introduced and everybody went behind that. Now its the time everybody again going to dynamic typing. May be its because of JavaScript's success.

VB always gave us the option to have dynamic typing. But in C# its introduced with .Net 4.0. The dynamic keyword is introduced to denote the variables which are not type safe. In other words a type which we don't know at compile time, what it is going to contain. Kind of key value store / dictionary.

Enough theory. Below is the code to convert a GitHub API response. The API url is 

private Project GetProjectFromJSON(string json)
    JavaScriptSerializer ser = new JavaScriptSerializer();
    dynamic projectNode = ser.Deserialize<dynamic>(json);
    return new Project()
        Name = projectNode["name"],
        Description = projectNode["description"],
        SourceUrl = projectNode["html_url"],
        Url = projectNode["homepage"]

JavaScriptSerializer is a .Net framework class. We don't need to add any dependency to third parties. There are other .Net libraries which are helping to convert JSON to dynamic object but those will add unwanted dependencies. Hope this is self explanatory.

Important thing to note here is the usage of dynamic. Do not ever return dynamic to outer world. This method should hide the complexities of getting the project from GitHub. The consumers of this method then don't need to change when the logic of GitHub API interaction changes.

More details about usage in real application can be seen in this file.

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