[9.0][REF]stock_auto_move: fix action_assign() (OCA#373)

* The `_apply` method should not be overridden. In case of three step
operation with the last step set to auto move. The override of the
`_apply` method was causing the second move to be automatic as well.

**Use case**: doing a reception operation in two steps where the moves on
the second step are set to be automatic (using the push rule in this
case), and the reception is done partially.
**Expected Result**: When doing a first reception step partially a back
order is created, and we expect the second step to have a back order for
the remaining qty as well.
**Current behavior**: The correct move is processed automatically but no
backorder is created. The reason for that behavior is we processing the
move directly (i.e calling `action_done` of the `stock.move`) without
going through the normal process (i.e processing the second step
picking).
**The solution to the problem**: The processing the of the automatic
stock move should follow the same behavior as done from the user interface.
I've added a new function in `stock.picking` model called
`_transfer_pickings_with_auto_move` to simulate the same behavior this
function is called inside the `action_assign` of the stock move instead
of calling the `action_done` of the move.

stock_auto_move/models/stock_auto_move.py

@@ -12,15 +12,43 @@ class StockMove(models.Model):
         help="If this option is selected, the move will be automatically "
         "processed as soon as the products are available.")
 
+    @api.model
+    def _get_auto_moves_by_pickings(self, auto_moves):
+        """ Group moves by picking.
+        @param auto_moves: stock.move data set
+        @return dict dict of moves grouped by pickings
+        {stock.picking(id): stock.move(id1, id2, id3 ...), ...}
+        """
+        auto_moves_by_pickings = dict()
+        for move in auto_moves:
+            if move.picking_id in auto_moves_by_pickings:
+                auto_moves_by_pickings[move.picking_id] |= move
+            else:
+                auto_moves_by_pickings.update({move.picking_id: move})
+        return auto_moves_by_pickings
+
     @api.multi
     def action_assign(self, no_prepare=False):
-        super(StockMove, self).action_assign(no_prepare=no_prepare)
-        # Transfer all pickings which have an auto move assigned
-        moves = self.filtered(lambda m: m.state == 'assigned' and m.auto_move)
-        todo_pickings = moves.mapped('picking_id')
-        # We create packing operations to keep packing if any
-        todo_pickings.do_prepare_partial()
-        moves.action_done()
+
+        already_assigned_moves = self.filtered(
+            lambda m: m.state == 'assigned')
+
+        not_assigned_auto_move = self - already_assigned_moves
+
+        res = super(StockMove, self).action_assign(
+            no_prepare=no_prepare)
+
+        # Process only moves that have been processed recently
+        auto_moves = not_assigned_auto_move.filtered(
+            lambda m: m.state == 'assigned' and m.auto_move)
+
+        # group the moves by pickings
+        auto_moves_by_pickings = self._get_auto_moves_by_pickings(auto_moves)
+
+        # process the moves by creating backorders
+        self.env['stock.picking']._transfer_pickings_with_auto_move(
+            auto_moves_by_pickings)
+        return res
 
     @api.multi
     def _change_procurement_group(self):

stock_auto_move/models/stock_picking.py

@@ -0,0 +1,34 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 ACSONE SA/NV
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from odoo import api, models
+
+
+class StockPicking(models.Model):
+
+    _inherit = 'stock.picking'
+
+    @api.model
+    def _transfer_pickings_with_auto_move(self, auto_moves_by_pickings):
+        """This function is meant to simulate what a user would normally
+        transfer a picking from the user interface either partial processing
+        or full processing.
+        @params auto_moves_by_pickings: dict of moves grouped by pickings
+        {stock.picking(id): stock.move(id1, id2, id3 ...), ...}
+        """
+        for picking in auto_moves_by_pickings:
+            if len(picking.move_lines) != len(auto_moves_by_pickings[picking]):
+                # Create a back order for remaning moves
+                backorder_moves = \
+                    picking.move_lines - auto_moves_by_pickings[picking]
+                picking._create_backorder(backorder_moves=backorder_moves)
+
+            # Create immediate transfer wizard so it will fill the qty_done
+            # on the auto move linked operation
+            picking.do_prepare_partial()
+            wizard = self.env['stock.immediate.transfer'].create(
+                {'pick_id': picking.id})
+            wizard.process()
+
+        return