在典型的微服务体系结构中，如何在微服务的单独的RDBMS数据库中链接相关数据？

Question

Let us say that I am designing an e learning portal where in a user can choose the courses he wishes to take and then do the payment online and then he/ she can use the courses.So I have modules like 1) Courses 2) Payments 3) User management. I choose to design 3 separate microservices ie a) Courses b) Payments and c) User management based on the domain. Now if this system was a monolith then we could have used a foreign key and would have linked the user , courses and payments tables for relating the data. Now since these 3 are different micro-services and will have its own databases, then how is the data linked together? ie If I want to relate that a particular user 'X' has enrolled to 'A','B','C' courses?

Answer 1

The micro service consumer of another other micro service can store identifiers of a specific external resource and relate it logically to its own resources in its database (RDBMS or any DB type).
That is not a database constraint relation but if this constraint is a have to, you can of course add some check about its presence and its consistency.

Supposing that the relation between the micro services be :

User Management  ->  Courses
                uses

The User Management could store resource identifiers of Courses resources associated to Users.
In this way you have a way to join the data of two domains in a specific way.
If the other dependency way is necessary ( Courses -> User Management), nothing prevents you to perform the same logical.

Not your question but important consequence of data relationship between micro service : data update of external resources have to be handled. Pull, push ? With or without cache ? It essentially depends on your use cases.