Get value in dropdown, Codeigniter

I want to edit/update the value of an item but I can't get its value from database. I have something like this in my database

Products table
   -id
   -category_id
   -sub_category_id
   -name
Category table
   -id
   -category
Sub Category table
   -id
   -sub_category

In my form, I have something like this. What should I do if the category_id in my products table exist, it should display its corresponding category name? I tried to use something like this in my form

<div class="form-group">
    <label for="" class="control-label"> Category</label>
        <select name="category_id" id="category" class="custom-select select">
            <option value="">Select Category</option>
               <?php
                   foreach ($category as $row) {
                       echo '<option value="' . isset($products->category_id) ? $row['id'] : ''  . '">' . $row['category'] . '</option>';
                 }
               ?>
      </select>
   </div>
<div class="form-group">
 <label for="" class="control-label">Sub Category</label>
      <select name="sub_category_id" id="subcategory" class="custom-select select">
<option value="<?php isset($products->sub_category_id) ? $products->sub_category_id : ''; ?>">Select Sub Category</option>
</select>
</div>

Here's my controller

 public function edit_product($id)
{
    $data['title'] = 'Update Product';

    $this->load->view('../admin/template/admin_header');
    $products = new Admin_model;
    $data['category'] = $this->Admin_model->category();
    $data['products'] = $products->edit_product($id);
    $this->load->view('../admin/template/admin_topnav');
    $this->load->view('../admin/template/admin_sidebar');
    $this->load->view('../admin/products/manage_product', $data);
    $this->load->view('../admin/template/admin_footer');
}

And my model

public function edit_product($id)
{
    $query = $this->db->get_where("products", array('id' => $id));
    return $query->row();
}

public function category()
{
    $response = array();

    $this->search(array(), 'date_created');

    $this->db->select('*');
    $query = $this->db->get('categories');
    $response = $query->result_array();

    return $response;
}

Solution

For each category that you're printing in the select box, check if the category id is the same as the product's category id. If they're the same, add 'selected' to the option:

           <?php
               foreach ($category as $row) {
                   echo '<option value="' . $row['id'] . '"';
                   if ($row['id'] == $products->category_id) {
                        echo ' selected'
                   }
                   echo '>' . $row['category'] . '</option>';
             }
           ?>

This selects the product's category name.

If your subcategory has a parent_id, the method to get all the subcategories for a certain category would look something like this (model):

public function sub_category($parent_id) {
    return $this->db->get_where('subcategories', array('parent_id' => $parent_id)->result_array();
}

Controller:

 public function edit_product($id)
{
    $data['title'] = 'Update Product';

    $this->load->view('../admin/template/admin_header');
    $products = new Admin_model;
    $data['products'] = $products->edit_product($id);
    $data['category'] = $this->Admin_model->category();
    $data['subcategory'] = $this->Admin_model->sub_category($data['products']->category_id);
    $this->load->view('../admin/template/admin_topnav');
    $this->load->view('../admin/template/admin_sidebar');
    $this->load->view('../admin/products/manage_product', $data);
    $this->load->view('../admin/template/admin_footer');
}

And select the product's subcategory in the view:

       <?php
           foreach ($subcategory as $row) {
               echo '<option value="' . $row['id'] . '"';
               if ($row['id'] == $products->sub_category_id) {
                    echo ' selected'
               }
               echo '>' . $row['sub_category'] . '</option>';
         }
       ?>

You would probably also need to add some Javascript to your view to load the corresponding subcategories when the value of the category select is changed, but that's going too far off topic for this question to explain here.

When using the same form for insert and update, check if $products exists first:

       <?php
           foreach ($category as $row) {
               echo '<option value="' . $row['id'] . '"';
               if (isset($products) && $row['id'] == $products->category_id) {
                    echo ' selected'
               }
               echo '>' . $row['category'] . '</option>';
         }
       ?>