mymodel_select_all

--- models.py ---
class MyModel(Model):
    picking = fields.Many2one(comodel_name='stock.picking')
    operations = fields.One2many(comodel_name='stock.pack.operation',
                                 related='return_picking.pack_operation_ids',
                                 readonly=True,
                                 states={constants.States.NEW:
                                         [('readonly', False)]},)

    # necessary for a second operations field in view
    operations_aux = fields.One2many(comodel_name='stock.pack.operation',
                                     related='operations',
                                     select=True)

    @api.multi
    def _get_scheduled_operations(self):
        operations = self.operations.search( # results in an empty recordset
            [('scheduled_for_operation', '=', True)])

        operations.write({'scheduled_for_operation': False}) # invalidate the ones that were retrieved
        return operations

    @api.one
    def delete_selected_operations(self):
        self._get_scheduled_operations().unlink()


class StockPackOperationExtension(Model):
    _inherit = 'stock.pack.operation'

    scheduled_for_operation = fields.Boolean(default=False)

--- xml view ---

<button type="object" name="delete_selected_operations" string="Delete Selected" class="oe_edit_only" attrs="{'invisible': ['!', '|', ('state','=','draft'), ('state','=','new')]}"/>

<!-- START: OPERATIONS FIELD-->
<!-- Operations in Edit Mode-->
<field name="operations" class="oe_edit_only">
    <tree editable="bottom" create="false">
        <field name="scheduled_for_operation" string="Select"/> <!-- Extra field in edit mode -->
        ... bla bla other fields ...
    </tree>
</field>

<!-- Operations in Read Only Mode-->
<field name="operations_aux" class="oe_read_only">
    <tree editable="bottom" create="false">
     ... bla bla fields ...
    </tree>
</field>
<!-- END: OPERATIONS FIELD -->