title: set values in form fields in edit mode when data comes from multipal tables
body: <p>I am developing a custom module for a project. I created a custom form and that custom form's data saved in two tables. Now when form open in edit mode I am not able to get saved data from both tables. I have no idea how can I get resolve this issue, please help me.</p>
  
  <p>Here are my two tables structures:</p>
  
  <p>Table1-</p>
  
  <pre><code>-------------------------
  id | page_id | title
  
  1  |  3      |  ABC
  
  2  | 4       |  PQRS
  
  3  | 10      |  XYZ
  </code></pre>
  
  <p>Table2-</p>
  
  <pre><code>--------------------------------
  id | page_id | child  | position
  
  1  | 3       |  8     |  left
  
  2  | 3       |  7     |  right
  
  3  | 3       |  15    |  right
  
  4  | 4       |  14    |  right
  
  5  | 4       |  15    |  left
  
  6  | 10      |  15    |  left
  
  --------------------------------
  </code></pre>
  
  <p>Here i am attaching a screen-shot to more explain myself. I want to selected saved option values in 'left' &amp; 'right' text-area  in edit mode, values comes from table2.</p>
  
  <p><img src="https://i.stack.imgur.com/xwGqP.jpg" alt="form fields"></p>
  
  <p>Please suggest me. Thanks in advance.</p>