web-api POST body object always null

Solution 1:

FromBody is a strange attribute in that the input POST values need to be in a specific format for the parameter to be non-null, when it is not a primitive type. (student here)

Try your request with {"name":"John Doe", "age":18, "country":"United States of America"} as the json.
Remove the [FromBody] attribute and try the solution. It should work for non-primitive types. (student)
With the [FromBody] attribute, the other option is to send the values in =Value format, rather than key=value format. This would mean your key value of student should be an empty string...

There are also other options to write a custom model binder for the student class and attribute the parameter with your custom binder.

Solution 2:

I was looking for a solution to my problem for some minutes now, so I'll share my solution.

When you have a custom constructor within your model, your model also needs to have an empty/default constructor. Otherwise the model can't be created, obviously. Be careful while refactoring.

Solution 3:

I spend several hours with this issue... :( Getters and setters are REQUIRED in POST parameters object declaration. I do not recommend using simple data objects (string,int, ...) as they require special request format.

[HttpPost]
public HttpResponseMessage PostProcedure(EdiconLogFilter filter){
...
}

Does not work when:

public class EdiconLogFilter
{
    public string fClientName;
    public string fUserName;
    public string fMinutes;
    public string fLogDate;
}

Works fine when:

public class EdiconLogFilter
{
    public string fClientName { get; set; }
    public string fUserName { get; set; }
    public string fMinutes { get; set; }
    public string fLogDate { get; set; }
}

Solution 4:

If the any of values of the request's JSON object are not the same type as expected by the service then the [FromBody] argument will be null.

For example, if the age property in the json had a float value:

"age":18.0

but the API service expects it to be an int

"age":18

then student will be null. (No error messages will be sent in the response unless no null reference check).

Solution 5:

This is a little old one and my answer will go down to the last place but even so I would like to share my experience.

Tried every suggestion but still having the same "null" value in a PUT [FromBody].

Finally found it was all about Date format while JSON serializing the EndDate property of my Angular Object.

No error was thrown, just received an empty FromBody object....