Session value to array - php

Question

I have this function that save data after the button is clicked.
$data=$_POST;
$details = array();
$details['title'] = $data['title'];
$details['content'] = $data['text'];
$details['snippet'] = $data['hidden_snippet'];
$details['createdDate']=date('Y-m-d H:i:s');
$result=$this->ask_model->book_add($details);
I want to add the session value which contains the user id from another table in a column named "author_id" .
$data= $this->session->userdata('user_id');
I tried to do this but the value I'm getting is null.
$data= $this->session->userdata('user_id');
$data=$_POST;
$details = array();
$details['title'] = $data['title'];
$details['content'] = $data['text'];
$details['snippet'] = $data['hidden_snippet'];
$details['createdDate']=date('Y-m-d H:i:s');
$details['author_id']= $data;
$result=$this->ask_model->book_add($details);
Here's the error:
Errors
What do I need to convert the session value into so I could add it to the array?
Update:
OK I'm a beginner at CodeIgniter and this problem is because of my own stupidity. The model I used was not set on $autoload['model'] on autoload.php plus I've been calling the wrong url in my ajax at my view file. The comments does solve one of my problem so thank you so much!

Answer 1

I think you are replacing data unnecessarily. This way I think you should do it
$user_id= $this->session->userdata('user_id');
$data=$_POST;
$details = array();
$details['title'] = $data['title'];
$details['content'] = $data['text'];
$details['snippet'] = $data['hidden_snippet'];
$details['createdDate']=date('Y-m-d H:i:s');
$details['author_id']= $user_id;
$result=$this->ask_model->book_add($details);

Answer 2

First load model in application/config/autoload.php
$autoload['model'] = array('Ask_model');
Make sure the first letter of file and class name should be capitalized. It should be Ask_model not ask_model
$data = $_POST overwriting the value of $this->session->userdata('user_id') because you are also giving the same variable name.
Overwriting here
$data= $this->session->userdata('user_id');
$data=$_POST;
Do like this
$author_id = $this->session->userdata('user_id');
$data=$_POST;
$details = array();
$details['title'] = $data['title'];
$details['content'] = $data['text'];
$details['snippet'] = $data['hidden_snippet'];
$details['createdDate']=date('Y-m-d H:i:s');
$details['author_id']= $author_id ;
$result=$this->ask_model->book_add($details);