MissingMethodException showing up on save action - exception

Question

I'm working an example from Grails in Action, specifically implementing a Service for the first time and shifting the work from the Controller to the Service.
I have a Post object containing a User and String content.
The service code is
class PostService {
boolean transactional= true
Post createPost(String user, String content){
def thisUser = User.findByUserID(user)
if (user){
def post = new Post(content:content)
if (user.save()){
return post
} else
throw new PostException(message: "Invalid post", post:post)
}
throw new PostException(message:"Invalid User ID")
}
}
and the controller code is
def addPost = {
try{
def newPost = postService.createPost(params.id, params.content)
flash.message= "Added new Post: $newPost.content}"
} catch (PostException pe){
flash.message = pe.message
}
redirect(action:'timeline', id:params.id)
}
The way this code is supposed to work is an input is made in the form, which is passed to addPost as a params object. Said params object is then handed off to the Service, where a new Post is to be made and bound to the User.
However, I'm getting the error at user.save(). The specific error message is
No signature of method: java.lang.String.save() is applicable for argument
types: () values: []
If I erase the service connector and implement the service code in the controller as
def user = User.findByUserID(params.id)
if (user) {
def post= new Post(params)
user.addToPosts(post)
if (user.save()){
flash.message= "Sucessfully created Post"
}
else {
user.discard()
flash.message = "Invalid or empty post"
}
} else {
flash.message = "Invalid User ID"
}
redirect(action: 'timeline', id:params.id)
}
the action works. So why am I getting a user.save() error on the service implementation, but not the controller?

Answer 1

user is the String you're passing to the service method. thisUser is the actual User object you're getting that you can call save() on.