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Pass multiple complex objects to Web API action

Working with ASP.NET Web API, the most unexpected thing is the limited support of POST data values to simple ApiController methods.

When a parameter has [FromBody], Web API uses the Content-Type header to select a formatter. At most one parameter is allowed to read from the message body. The reason for this rule is that the request body might be stored in a non-buffered stream that can only be read once.

A simple principle, you can send any content in HTTP request, it only need to be serializable into a string. So, it could be multiple JSON object. In this example, the content type is "application/json" and the request body is a raw JSON string (not a JSON object).

Here I found a workaround to pass multiple complex objects (using the above principle) from jquery to a WEB API using JObject, and then cast back to your required specific object type in api controller. This objects provides a concrete type specifically designed for working with JSON.

var customer = {
"Name": "jhon",
"Id": 1,
};
var product = {
"Name": "table",
"CategoryId": 5,
"Count": 100
};
var employee = {
"Name": "Fatih",
"Id": 4,
};

var combinedObj = {}; 
combinedObj["obj1"] = customer; 
combinedObj["obj2"] = product; 
combinedObj["obj3"] = employee;

$.ajax({
type: 'POST',
async: true, 
url: 'api/PostGenericObjects/',
data: JSON.stringify(combinedObj),
success: function (response) {
console.log("Response Data ↓");
console.log(response);
},
error: function (err) {
console.log(err);
}
});


and then you can get this object in your ApiController

using Newtonsoft.Json.Linq;

public string PostGenericObjects(object obj)
{
string[] str = GeneralMethods.UnWrapObjects(obj);
var customer = JsonConvert.DeserializeObject<Customer>(str[0]);
var product = JsonConvert.DeserializeObject<Product>(str[1]); 
var employee = JsonConvert.DeserializeObject<Employee>(str[2]);

//... other work....

}  

I have made a generic function to unwrap the complex object, so there is no limitation of number of objects while sending and unwrapping. We can even send more than two objects

public class GeneralMethods
{
  public static string[] UnWrapObjects(object obj)
  {
    JObject o = JObject.Parse(obj.ToString());

    string[] str = new string[o.Count];

    for (int i = 0; i < o.Count; i++)
    {
      string var = "obj" + (i + 1).ToString();
      str[i] = o[var].ToString();
    }
    return str;
  }
}



I hope it would help someone. I would be interested to hear from the experts here regarding the pros and cons of using this methodology. Do share your feedback.

Happy Coding!


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