Error undefined offset: 2 in php code-igniter

Question

I want delete user and user role by using checkbox. first check then submit button click. After click, selected user and user_role should be deleted.

got php undefined offset 2 error on line 491

this is my model:

public function add_participation(){
    $user = $this->input->post('user');
    $role = $this->input->post('role');
    $delete = $this->input->post('delete');
    for($i=0;$i<count($user);$i++){
        if($user[$i] !=""){

            $this->db->where('workflow_activity_id',$this->input->post('batch'));
            $this->db->where('role_id',$role[$i]);
            $this->db->where('user_id',$user[$i]);
            $exist = $this->db->get('workflow_participation');  

            $data = array(
                'user_id'                   => $user[$i],
                'role_id'                   => $role[$i],
                'workflow_activity_id'      => $this->input->post('batch'),
            );
            if($exist->num_rows() == 0){
                $this->db->insert('workflow_participation',$data);
            }else{
                $this->db->where('workflow_activity_id',$this->input->post('batch'));
                $this->db->where('role_id',$role[$i]);
                $this->db->where('user_id',$user[$i]);              
                $this->db->update('workflow_participation',$data);
            }                
                if($delete[$i] == '1'){  //**error on this line**
                $this->db->where('workflow_activity_id',$this->input->post('batch'));
                $this->db->where('role_id',$role[$i]);
                $this->db->where('user_id',$user[$i]);
                $this->db->delete('workflow_participation');
            }
        }
    }
    return true;
}

In this view page user and user_role show in drop-down.

This is my view page

<div class="form-group">
<label class="control-label col-md-3">User :</label>
<div class="col-md-8">
    <select id="user" name="user[]" class="select form-control">
        <option value="" selected="selected">-------</option>
        <?php 
        if(!empty($user)){
        foreach($user as $user_result){?>
            <option value="<?=$user_result->id;?>" <?php if(!empty($participent) && !empty($participent[1]) && $participent[1]->user_id == $user_result->id){?>selected="selected"<?php }?>><?=$user_result->username;?></option>
        <?php }}?>
    </select>
</div>
<label class="control-label col-md-3">Role :</label>
<div class="col-md-8">
    <select id="role" name="role[]" class="select form-control">
        <option value="" selected="selected">-------</option>
        <?php 
        if(!empty($role)){
            foreach($role as $role_result){?>
        <option value="<?=$role_result->id;?>" <?php if(!empty($participent) && !empty($participent[1]) && $participent[1]->role_id == $role_result->id){?>selected="selected"<?php }?>><?=$role_result->name;?></option>
        <?php }}?>
    </select>
</div>
<label class="control-label col-md-3">Delete :</label>
<div class="col-md-8">
    <input type="checkbox" name="delete[]" value="1">
</div>

Answer 1

First check if the variable $role have the same amount of data as $user, if it's not so you have a problem.

Next for the line for($i=0;$i<count($user);$i++) , create an outside variable for your count, here everytime you enter the for, the count() is called, bad optimisation.

Answer 2

Since you are using delete[] as array, i hope your view is in a loop. a checkbox value is submitted only when it is checked. So you will receive your input in wrong order. ie, you selected first user and role and checked last delete, you may receive delete for first user. The second and third delete will be undefined. Please see this link for details and hidden field hack for this issue

So I suggest change the following 3 lines in your html as following. you can use $participent[1]->user_id ( or a counter) as index in view file.

<select id="user" name="user[<?php echo $participent[1]->user_id;?>]" class="select form-control">
...
<select id="role" name="role[<?php echo $participent[1]->user_id;?>]" class="select form-control">
...
<input type="checkbox" name="delete[<?php echo $participent[1]->user_id;?>]" value="1">

change the loop from this

for($i=0;$i<count($user);$i++){

to

foreach( $user as $i => $unused ) {

Then instead of equal checking

if($delete[$i] == '1'){  //**error on this line**

use

if( isset($delete[$i]) ){  //**error on this line**
    // if( $delete[$i] == '1' ){  //uncomment if you need double confirmation