Assuming to create an App that manages the admin side of the quotes, how can I store this data?
The scenario is simple, there is a "Quotation" entity that has a relationship with the already existing entities: Customer and Products.
There does not seem to be the possibility of creating a custom object (in this case Quotation). How should it be managed in Shopify logic?
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This is an accepted solution.
Shopify doesn't give developers access to its database to store custom objects like this.
If I understand correctly what you're trying to achieve, then in order to create 'Quotations' that are connected to customers and products, you will need to develop a standalone web application that connects to a database (for example MySQL or Postgres). You could use then the Shopify Admin API and webhooks to communicate with your application to fetch and store product and customer data alongside quotations.
Shopify has a great blog post on how to get started developing Apps in this way: https://www.shopify.com/partners/blog/how-to-build-a-shopify-app
Is this the kind of thing you're trying to achieve?
You won't be able to fetch your own data (i.e. Quotations) through the Shopify GraphQL API. Instead you will have to communicate with your own API connected to your database which in turn should fetch data from the Shopify API.
You can of course choose to make your own GraphQL API. Some good starting points for building APIs with if you're not a developer or don't have much experience building APIs are tools like Strapi and Hasura.
Very clear, I wanted to understand if an internal data merge logic was available, instead it seems to be a business logic to keep the shopify database intact so from this point of view it is understandable.
I am a developer and I am researching now on Shopify, before diving into the technical specifications I wanted to understand the Business Logic so as to facilitate the understanding of the choices made by Shopify.