Decrease stock as soon as a product is added to cart

also we need to consider abandoned orders. this can be handled using Commerce Cart Expiration.
I think we had a similar issue before may not have the answer for you but worth tracking it down.

@idflood, how did you get on with this, did you manage to resolve your issue with the "After deleting a commerce order" rule?

@idflood, would you happen to have any screenshots of how you set this up on your rules pages?

I'm creating an events ticket purchasing site and need the ability to have stock deducted once its added to the cart and have it added it back if the user doesnt process the order fully within 20 minutes.

This method - described in the issue summary - has a big problem: it calculates wrong values when a user tries to add the same product to the cart twice.

This is because the only input parameter for "decrease the product stock for a given line item" action is a line item. When you have a x product with qty 2 in the cart and try to add another 1, the line item will have a qty of 3 when calling this action. This means it will decrease the stock by 3 not by 1.

I have solved this problem by manually calculating the stock amount:

{ "rules_commerce_ss_stock_decrease_when_adding_to_cart" : {
    "LABEL" : "Decrease stock when adding to cart",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "TAGS" : [ "stock_control" ],
    "REQUIRES" : [ "rules", "commerce_cart" ],
    "ON" : { "commerce_cart_product_add" : [] },
    "DO" : [
      { "data_calc" : {
          "USING" : {
            "input_1" : [ "commerce-product:commerce-stock" ],
            "op" : "-",
            "input_2" : [ "quantity" ]
          },
          "PROVIDE" : { "result" : { "new_quantity" : "New Quantity" } }
        }
      },
      { "data_set" : {
          "data" : [ "commerce-product:commerce-stock" ],
          "value" : [ "new-quantity" ]
        }
      }
    ]
  }
}

This works well in conjunction with the increase method described in the issue summary:

{ "rules_increase_stock_when_item_removed_from_cart" : {
    "LABEL" : "Increase stock when item removed from cart",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "TAGS" : [ "stock_control" ],
    "REQUIRES" : [ "commerce_ss", "commerce_cart" ],
    "ON" : { "commerce_cart_product_remove" : [] },
    "DO" : [
      { "commerce_ss_increase_by_line_item" : { "commerce_line_item" : [ "commerce-line-item" ] } }
    ]
  }
}

But this method has problems too:
- When you try to modify the amounts on the cart page, it won't affect the stock.
- When you modify the quantity of an item on the cart page and press the remove button (instead of update cart), it will increase the stock by the entered value, not the original qty.

This can be avoided by disabling the editable quantity field in cart view.

@roland.molnar

This seems to solve your first issue:

{ "rules_test" : {
    "LABEL" : "Test",
    "PLUGIN" : "reaction rule",
    "REQUIRES" : [ "rules", "entity" ],
    "ON" : { "commerce_line_item_update" : [] },
    "IF" : [
      { "entity_has_field" : { "entity" : [ "commerce-line-item" ], "field" : "commerce_product" } }
    ],
    "DO" : [
      { "data_calc" : {
          "USING" : {
            "input_1" : [ "commerce-line-item:quantity" ],
            "op" : "-",
            "input_2" : [ "commerce-line-item-unchanged:quantity" ]
          },
          "PROVIDE" : { "result" : { "net_quantity" : "Net quantity" } }
        }
      },
      { "data_calc" : {
          "USING" : {
            "input_1" : [ "commerce-line-item:commerce-product:commerce-stock" ],
            "op" : "-",
            "input_2" : [ "net-quantity" ]
          },
          "PROVIDE" : { "result" : { "new_product_quantity" : "New product quantity" } }
        }
      },
      { "data_set" : {
          "data" : [ "commerce-line-item:commerce-product:commerce-stock" ],
          "value" : [ "new-product-quantity" ]
        }
      }
    ]
  }
}

I have started work on this problem in a module called Commerce Stock Reserve. Please have a look and see if it meets your needs.

Hi pjcdawkins
That's exiting news. it would good to give more details about the technical implementation and how it interacts with commerce stock. I created an issue on your project and looking forward to spend more time looking at the module.

Marking this fixed as Commerce Stock Reserve does what is requested.

Required functionality for commerce 2 (drupal 8) How to do it?