Empty Json Array is received on Post

Question

i have an MVC application that is calling a web api to pass some data.

MVC-code

     [AcceptVerbs(HttpVerbs.Post)]
    public async System.Threading.Tasks.Task<ActionResult> StudentViewModels_Create([DataSourceRequest]DataSourceRequest request, [Bind(Prefix = "models")]IEnumerable<StudentViewModel> studentviewmodels)
    {
        using (System.Net.Http.HttpClient client = new System.Net.Http.HttpClient())
        {
            string  baseUrl = "http://localhost:51514/api/Students";
            client.BaseAddress = new Uri(baseUrl);
            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));

            JArray postData = new JArray();
            //postData.Add(JsonConvert.SerializeObject(request));
            foreach(StudentViewModel student in studentviewmodels)
            {
                postData.Add(JsonConvert.SerializeObject(student));
            }
           // call the web-api and pass the data
           System.Net.Http.HttpResponseMessage response = await client.PostAsync(baseUrl, new StringContent(new JavaScriptSerializer().Serialize(postData), Encoding.UTF8, "application/json"));
            if (!response.IsSuccessStatusCode)
            {
                var data = response.Content.ReadAsStringAsync();
            }
        }

        // this will return new data
        //return Json("");
    }

here is picture of the data that is in postData variable before it is sent

However, when the call reaches the Api, the Json array is empty.

Web-api

    public  IHttpActionResult Students_Create(JArray inputData)
    {

        var students = new List<Student>();

        for (int i = 1; i<inputData.Count; i++)
        {
            var tempStudent = new Student();
            tempStudent = (Student)JsonConvert.DeserializeObject(inputData[i].ToString());
            students.Add(tempStudent);
        }

        // Will keep the inserted entitites here. Used to return the result later.
        var entities = students;
        if (ModelState.IsValid)
        {
            using (var northwind = new StudentEntities())
            {
                foreach (var student in students)
                {
                    // Create a new Student entity and set its properties from the posted StudentViewModel.
                    var entity = new Student
                    {
                        Studentid = student.Studentid,
                        Firstname = student.Firstname,
                        Lastname = student.Lastname,
                        Age = student.Age
                    };
                    // Add the entity.
                    northwind.Students.Add(entity);
                    // Store the entity for later use.
                    entities.Add(entity);
                }
                // Insert the entities in the database.
                northwind.SaveChanges();
            }
        }

        return Json(db.Students);
    }

picture of inputData variable

Any ideas as to why this is happening?. thanks for the help.

Answer 1

Not an answer, but more of an observation of the code you provided. You don't appear to be calling your Students_Create method anywhere in the StudentViewModels_Create . Which leads me to believe you are passing the returned result of StudentViewModels_Create to Students_Create which will not work since StudentViewModels_Create returns an empty Json object ( return Json("") ).

Answer 2

The problem is with the Json Array. this piece of code in the MVC-code section

        JArray postData = new JArray();
        //postData.Add(JsonConvert.SerializeObject(request));
        foreach(StudentViewModel student in studentviewmodels)
        {
            postData.Add(JsonConvert.SerializeObject(student));
        }

when i pass the array through the serializer

       var serializer = new JavaScriptSerializer();
       var json = new System.Web.Script.Serialization.JavaScriptSerializer().Serialize(postData);
       var stringContent = new StringContent(json, Encoding.UTF8, "application/json");

       // pass the data to the api
       System.Net.Http.HttpResponseMessage response = await client.PostAsync(baseUrl, stringContent);

the json varaible only contains an empty array, so what is passed to the api, is an empty array. hence why i was only getting an empty array.

I decided to try an ArrayList instead of a JArray, then passed it through the serializer and it worked. I am not 100% certain as to why this solved the issue, i am still researching for a concrete reason.

        ArrayList postData = new ArrayList();
        postData.Add(JsonConvert.SerializeObject(request));
        foreach (StudentViewModel student in studentviewmodels)
        {
            postData.Add(JsonConvert.SerializeObject(student));
        }