ASP.Net WebAPI - What is idempotent using Post and PUT - asp.net-web-api

Question

I am new developer and i have not much knowledge on http service. so i was finding the difference between PUT and POST. i read this one https://forums.asp.net/t/2100831.aspx?WebApi+what+is+difference+between+PUT+and+POST
below things not clear specially what is idempotent?
i found one guy said - The PUT method is defined to be idempotent ( ie : have the same result over subsequent calls ). PUT would always update the same resource and return 200 status code.
But POST would create a new resource and return 201 status code.
anyone would mind to explain why PUT is considered as idempotent. thanks

Answer 1

From a pure RESTful point of view PUT is considered idempotent because it does not matter how many times you make the same request, the result will be the same.
However, this being said, don't forget that the object you are trying to update might have its state changed between these identical PUT requests so the response you get might not actually be the same.
This does not mean that if you fire 100 PUT requests only one goes through though like in a previous response.
One more thing, just to be clear, POST is used to create new resources and typically returns the unique identifier of the created resource.
PUT is used to update resources and typically returns the entire updated resource so you can see what changes have been made to it.
There have been many discussions on what data should each of these accept, my personal view is that POST takes the fields required create the resource, no ID, while PUT takes the fields take will be updated and if the ID is part of the URL then it can be omitted again
for example, let's say you issue a PUT request to an endpoint like this:
api/users/1
where 1 is the id you need to identify this user, then your method could look like this:
[HttpPut]
public UserClass Put(int id, UserClass user)
{}
in this case your UserClass does not need the id as you already have it from the URL.
Hope all of this makes sense, I find the use of "idempotent" in a RESTful context quite confusing!

Answer 2

Let's say you want to update an User object so you call the PutUser method this way
$.ajax({
url: "yourUrl/PutUser/1",
type: 'PUT',
data: "firstName: fName, lastName: lName",
success: function(data) {
alert('User Updated.');
}
});
And your PutUser method looks like this
[HttpPut]
public dynamic PutUser(int id, UserClass user)
{}
In this case if you make the Ajax PUT request using the same parameters 1, 2..5 or N times the result will be identical, that is what idempotent means.
On the other hand if you have this
$.ajax({
url: "yourUrl/PostUser",
type: 'POST',
data: "firstName: fName, lastName: lName",
success: function(data) {
alert('User Updated.');
}
});
And your PostUser method looks like this
[HttpPost]
public dynamic PostUser(UserClass user)
{}
And call the PostUser method with the same parameters N times, you will Post N identical users and that could mean for example in 100 identical rows in your database, so all your calls will be processed.