Designing a database that handles inventory tracking with product variations

Question

I am designing a database for a project that handles inventory management for shops.

Basically, each Product can have the variations Color , and Size , and obviously, the number of products (stock) of each possible variation will vary.

Example:

[
    {
        "product": "Plain T-Shirt",
        "color": "Red",
        "size": "Medium",
        "stock": 10,
    },
    {
        "product": "Plain T-Shirt",
        "color": "Red",
        "size": "Large",
        "stock": 2,
    },

]

Here, the same product (Plain T-Shirt) has different stocks for different variations. As you can probably imagine, I need to be able to update each stock independently.

So, what would be the most efficient way to design such a database? I am using PostgreSQL, so the design needs to be relational, but I also have access to JSON fields.

Right now, my current design looks sort of like this:

Product

• Name (Character field)
• Quantities (JSON field)

Color

• Name (Character field)
• Product (Foreign Key of Many-to-One Relationship)

Size

• Name (Character field)
• Product (Foreign Key of Many-to-One Relationship)

The colors, and sizes can be dynamically added by the user, so the system has to compensate for that.

Regarding the Quantities field, lets say a product P1 has the colors 'Red', and 'Green', and the sizes 'S', and 'M'. I am trying to make the Quantities field something like this: 4 keys of all the possible combinations: (Red, S), (Red, M), (Green, S), (Green, M) with values representing the stock those variations currently have in inventory.

So, my question is this: Am I on the right path? Is this design effective or is there a better way to do this? Thanks.

Answer 1

The problem I see in your design is that for every product that is colored 'Red' you'd have a record for 'Red' in the colors table. Same with the sizes. And then using JSON to define the quantities would create a lot of opportunities for inconsistencies (eg if you delete a color from the colors table and then you forget to delete the quantity, it's not very 'relationy').

Here's how I would do it: Using a trenary relationship.

You tables would look something like this:

PRODUCTS(id,name,...)
COLORS(id,name,...)
SIZES(id,size_label,...)
STOCKS(id,product_id,color_id,size_id,quantity)

The STOCKS table represents the trenary relationship.

This way you can keep things separate enough and it's easier to keep track of your stock using a single query to do it.

Answer 2

You can use variations dynamically. The inventory table contains your variation_ids and product_ids. So you can easily track your inventories.