title: Data modelling: parent and child 'dual' relationship
body: <p>I am trying to create a proper parent/child relationship within my data model. I have a typical one to many relationship between the parent and children.</p>
  
  <p>I am wondering if I have parents that know about their children, is it </p>
  
  <ol>
  <li>ever acceptable, and  </li>
  <li>a good idea </li>
  </ol>
  
  <p>for each child to specifically know about its parent?. (a child can only have one parent in my case)</p>
  
  <pre><code>parent      
  -------------
  PARENT_ID
  OTHER_COL
  ...
  
  child
  -------------
  CHILD_ID
  PARENT_ID    // &lt;-- Should this column be here?
  OTHER_COL
  ...
  
  parent_has_children
  --------------------
  PARENT_ID
  CHILD_ID
  </code></pre>
  
  <p>The advantage I see for having the parent column in the child, is for easily retrieving the parent from a child. But, is this just lazy design?</p>
  
  <p>Thanks in advance.</p>