How to Properly Handle JSON POST Data with Model Binding in ASP.NET MVC4 Web API?

Passing JSON POST Data as an Object in Web API

ASP.NET MVC4 Web API applications often define POST methods to handle data submissions. When receiving JSON data in the request body, developers may encounter issues where POST parameters are set to null. To resolve this, it is important to ensure the correct usage of Content-Type and model binding.

Content-Type:

By default, ASP.NET uses Content-Type: application/x-www-form-urlencoded, which is not ideal for sending JSON data. To specify JSON, set Content-Type: application/json in your request headers.

Model Binding:

To enable model binding, decorate the POST method parameter with [FromBody]. This attribute specifies that the data should be bound from the request body rather than the URL query string.

Example:

In the provided example, the controller method expects a Customer object in the request body. To fix the null value issue, ensure that you specify Content-Type: application/json in your request headers and decorate the parameter with [FromBody] as follows:

public object Post([FromBody] Customer customer)

On the client side, use JSON.stringify to convert the Customer object to a JSON string before sending the POST request.

Complex Objects:

For more complex objects, such as objects with nested properties or lists, the same approach applies. Use JSON.stringify to serialize the object on the client side and ensure the correct Content-Type header is set.

Troubleshooting:

If model binding is not working correctly, consider the following:

• Ensure [FromBody] is applied to the method parameter.
• Verify that the Content-Type header is set to application/json in the request.
• Check if the model classes match the expected data structure on both the client and server sides.

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