Fix/force blocks in a region inside a tableDrag

Question

I'm trying to alter/patch/hack node_level_blocks (like the admin blocks overview page) so that some users are restricted in choosing regions for certain blocks. For instance the "New Content" view must always be in the Right region. The normal user can change the weight and add more blocks to that region, but they can't remove that block from that region.

What I did (I'm pretty close):

• Form alter the <select> to that it contains only 1 option
• Override Drupal.tableDrag.blocks.onDrag to fix and improve the standard tableDrag handler and make the row jump back to its forced position

That works, but the user can still drag the block around to regions it doesn't belong. (I don't have a demo online.)

How do I tell tableDrag to NOT let some blocks out of their original regions? I don't understand its 400 options...

Answer 1

The checking-magic comes from Drupal.tableDrag.prototype.row.prototype.isValidSwap and you can override that to add a custom validation. This solved my problem:

// onDomReady: override Drupal.tableDrag.prototype.row.prototype.isValidSwap to add swap-validation.
jQuery(function($) {
  if (Drupal.tableDrag) {
    var _isValidSwap = Drupal.tableDrag.prototype.row.prototype.isValidSwap;
    Drupal.tableDrag.prototype.row.prototype.isValidSwap = function(tr) {
      // Do standard tableDrag validation.
      var valid = _isValidSwap.apply(this, arguments);
      if (!valid) {
        return false;
      }

      // One of us?
      var $select = $('.form-select', this.element),
        loner = $select[0].options.length <= 1;
      if (loner) {
        // Can't swap with non-draggables, since that would mean a boundary.
        if (!$(tr).is('.draggable')) {
          return false;
        }

        // Can't skip over any rows, since that might be a boundary.
        var diff = tr.rowIndex - this.element.rowIndex;
        if (Math.abs(diff) > 1) {
          return false;
        }
      }

      return true;
    };
  }
});

All thanks to Mołot of course.