[ADD] inventory: Using product variants

https://docs.google.com/document/d/1VUg2ZMBMkEl78wN597cJfEP7EHNr66JKF9VKkRYU1Tw/edit

inventory/settings/products.rst

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+========
+Products
+========
+
+.. toctree::
+   :titlesonly:
+   :glob:
+
+   products/variants

inventory/settings/products/variants.rst

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+======================
+Using product variants
+======================
+
+Product variants are used to manage products having different
+variations, like size, color, etc. It allows managing the product at the
+template level (for all variations) and at the variant level (specific
+attributes).
+
+As an example, a company selling t-shirts may have the following
+product:
+
+- B&C T-shirt
+
+  - Sizes: S, M, L, XL, XXL
+  - Colors: Blue, Red, White, Black
+
+In this example, **B&C T-Shirt** is called the product template and
+**B&C T-Shirt, S, Blue** is a variant. Sizes and color are
+**attributes**.
+
+The above example has a total of 20 different products (5 sizes x 4
+colors). Each one of these products has its own inventory, sales, etc.
+
+Impact of variants
+==================
+
+- **Barcode**: the code and barcode is associated to a variant, not the
+  template. Every variant may have its own barcode / SKU.
+
+- **Price**: every product variant has its own public price that is
+  computed based on the template price ($20) with an optional extra
+  for every variant (+$3 for color red). However, you can define
+  pricelist rules that apply on the template or the variant.
+
+- **Inventory**: the inventory is managed by product variant. You don't
+  own t-shirts, you only own "T-shirts, S, Red", or "T-Shirts, M,
+  Blue". For information purpose, on the product template form, you
+  get the inventory that is the sum of every variant. (but the
+  actual inventory is computed by variant)
+
+- **Picture**: the picture is related to the variant, every variation
+  of a product may have its own primary picture.
+
+- **Other fields**: most of the other fields belongs to the product
+  template. If you update them, it updates automatically all the
+  variants. (example: Income Account, Taxes)
+
+Should you use variants?
+========================
+
+When should you use variants?
+-----------------------------
+
+Using variants has the following impacts:
+
+- **eCommerce**: in your online shop, the customer will only see
+  product templates in the catalog page. Once the visitor click on
+  such a product, he will have options to choose amongst the
+  variants (colors, sizes, …)
+
+- **Manufacturing**: Using variants allows to define only one bill of
+  material for a product template and slight variations for some of
+  the variants. Example: instead of creating a Bill of Material for
+  "T-shirt, Red, S", you create a bill of material for "T-shirt"
+  and add some lines that are specific to the dimension S, and
+  other lines specific to the color Red.
+
+- **Pricing**: The default price of a product is computed using the
+  price of the product template and add the optional extra price on
+  each dimension of the variant. This way, variant prices are
+  easier to maintain since you don't have to set the price for
+  every variant. However, it's possible to create pricelist rules
+  to fix price per variants too.
+
+When should you avoid using variants?
+-------------------------------------
+
+Using variants may add a level of complexity on the way you use Odoo.
+You should consider using variants only if you need it to reduce the
+complexity of managing lots of products that are similars.
+
+As an example, importing your initial product catalog is more complex if
+you use variants. You can't just import a list of products, you must
+import product templates and all their related variations.
+
+In addition to that, you should also carefully select the dimensions
+that you manage as separate product templates and those as variants. As
+an example, a company having these products:
+
+- Quality: T-Shirts, Polos, Shirts
+
+- Color: Red, Blue
+
+- Size: S, M, L, XL
+
+In such a use case, you could create 1 template with three dimensions of
+variants (Layout, T-Shirts, Polos). But, it's recommended to create two
+different product templates as T-shirts may highly differ from polos or
+shirts and customer expect to see these as two different products in the
+e-Commerce:
+
+- Product Template: T-shirt
+
+  - Color: Red, Blue
+  - Size: S, M, L, XL
+
+- Product Template: Polos
+
+  - Color: Red, Blue
+  - Size: S, M, L, XL
+
+Configuration
+=============
+
+Activate the variant feature
+----------------------------
+
+Before you can use product variants, you must first activate the product
+variants in the settings. To do so, you must go to the Sales app. In the
+menu :menuselection:`Configuration --> Settings`, locate the **Products Variants** line,
+and tick the option **Products can have several attributes**, then click
+on **Apply**.
+
+.. image:: media/variant01.png
+   :align: center
+
+Creating products with variants
+-------------------------------
+
+Once you have activated the variant option, you can add variants to your
+products. To do so, go to the Sales module, :menuselection:`Sales --> Products`.
+It is also accessible from the Purchase and inventory modules.
+
+Now, click on the product you wish to add variants to.
+
+In the product page, a new tab called Variants has appeared. The number
+in purple written on top is the number of variants this product
+currently has. To add new variants, click on the tile. In the new
+window, click on **Create**.
+
+In **Attributes**, click on the rolldown menu and select the type of
+variance you wish to add. If the variant does not yet exist, you can
+create it on the fly by clicking on Create and edit…
+
+.. image:: media/variant02.png
+   :align: center
+
+In the Attributes window, the **Value** field is the description of the
+attribute such as Green, Plastic or 32GB. The **Attribute** field is the
+type of variant such as Color, Material or Memory.
+
+.. image:: media/variant03.png
+   :align: center
+
+You can add a cost for the variant on the fly by adding it in the
+**Attribute Price Extra** field, or choose to modify it later. Click on
+**Save**.
+
+You can also add a different barcode and internal reference to the
+variant.
+
+When you have entered all the specifications of the variant, click on
+**Save**.
+
+Managing Product Variants
+=========================
+
+Introduction
+------------
+
+The examples below are all based on this product template that has two
+variant attributes :
+
+-  T-Shirt B&C
+
+   -  Color: Red, Blue, White
+
+   -  Size: S, M, L, XL, XXL
+
+Managing combination possibilities
+----------------------------------
+
+By default, with the above product template, you get 15 different
+products (3 colors, 5 sizes). If the XXL size does not exist for red and
+blue t-shirts, you can deactivate this product variant.
+
+To do this, click on the **Variants** button, select the XXL, White
+T-shirt. From the product form, uncheck the **Active** box of the T-shirt
+White, XXL.
+
+.. image:: media/variant04.png
+   :align: center
+
+.. tip::
+
+  That deactivating a product is different than having an inventory of 0.
+
+Setting a price per variant
+---------------------------
+
+You can add a cost over the main price for some of the variants of a
+product.
+
+Once you have activated the variant option, you can add variants to your
+products. To do so, go to the Sales module, open :menuselection:`Sales --> Products`
+and click on the product you want to modify. Click on the **Variant Prices**
+button to access the list of variant values.
+
+.. image:: media/variant05.png
+   :align: center
+
+Click on the variant name you wish to add a value to, to make the 3
+fields editable. In the **Attribute Price Extra** field, add the cost of
+the variant that will be added to the original price.
+
+.. image:: media/variant06.png
+   :align: center
+
+When you have entered all the extra values, click on **Save**.
+
+.. todo::
+
+  .. seealso::
+
+      * Accounting Memento: Details of Journal Entries
+      * Process Overview: From Billing to Payment Orders