Yes, it is a priority question. Below doc from stock. About priority in bold.

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Routes

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A Route is a collection of procurement rules and push rules. Routes can be applied on:

* Product

* Product Category

* Warehouse

* Sale Order Line (activated through setting Settings > Configuration > Sales > Choose MTO, Dropship, ... on sale order lines)

On the route itself you can specify if you let the user change it on one of the above models. For example, MTO and buy routes will simply be configured on the product level and then the user can choose the routes he want in the product form.

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How does the system choose the correct procurement rule

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When a sales order creates a procurement it passes some useful information to it. First, a sales order has a warehouse where the goods need to be picked up. This warehouse will be copied on the procurement. For example, when you have a procurement in Customers, but you know it has to be delivered from Warehouse WH, it can add a route with a procurement rule from WH/Stock to Customers and it will not apply a procurement rule from WH2/Stock to Customers. Second, it is possible to supply an extra route on the sale order line itself. This can come in handy when you decide on the sale order what route to follow e.g. if you sometimes decide to do dropshipping, you could enter it there. These routes are copied on the procurement related to the sale order line.

These routes on the procurement itself can also come in handy when the procurement can not find a suitable rule. By adding a route, you can solve the procurement according to the situation. (e.g. a certain product needs to be manufactured sometimes or bought sometimes)

When Odoo needs to find a procurement/push rule, it will check the routes that can be applied to the procurement as follows:

* It will try to find a rule from the route(s) on the procurement first

* If it does not find any, it will try to find a rule from the route(s) on the product and product category (+ its parents)

* If it does not find any there, it will try to find a rule from the route(s) on the warehouse

If in any of these cases, multiple rules are found, it will select the rule with the highest priority. This sequence can be changed in Warehouse > Routes (drag/drop the lines). Normally, this will play almost no role as configuring this way makes it really complex.

Actually, when you select MTO on a product, this is a route that is chosen. As in the basic configuration, it is defined on the product. (it is shown in the product form in a special widget that shows all the possible elements it could have in the one2many and you can select them) As such, this route will be chosen over the standard route and will have a rule that puts procure method "Create Procurement on Source" to stock. In the route MTO all such rules for all warehouses will be put in the standard configuration.

The reason behind such a configuration is that in most situations, the routes followed through the warehouse are the same for almost all products. The exceptions on it can be defined for certain product categories or products. Some things like MTO or buy/manufacture might be better to put on product level. And then it is still possible that you change your mind on the sales order line.

For the inter-warehouse configurations, there is also a possibility to put a warehouse on a procurement rule. These rules will only be applied if the warehouse on the procurement is the same.