21 - Services and Repositories

Overview of Services and Repositories

• Essential components in Nest applications to handle business logic and data storage.

Definitions

Services

• Classes responsible for implementing business logic.

• Used to perform calculations and handle requests for data.

• Often retrieve data from repositories.

Repositories

• Classes dedicated to storage-related logic.

• Interact directly with databases or any data storage (e.g., files).

• Manages reading and writing data from/to storage (e.g., a plain text file for messages).

Relationship Between Services and Repositories

• Services use one or multiple repositories to access and manipulate data.

• In this context:

  • Messages Repository: Manages a plain text file to store and retrieve messages.

  • Messages Service: Interacts with the repository to access messages.

Common Use Cases

• Services typically contain methods that closely resemble those in the corresponding repository.

• Example methods in Messages Repository:

  • findOne: Retrieve a specific message by ID.

  • findAll: Retrieve all messages stored in the file.

  • create: Add a new message to the file.

• Example methods in Messages Service:

  • findOne: Access a specific message using the repository's method.

  • findAll: Access all messages from the repository.

  • create: Create a new message, forwarding the request to the repository.

Purpose of Services in Nest

• Services act as a layer of abstraction over repositories, allowing for:

  • Combining data from multiple repositories.

  • Managing complex business logic that may involve multiple data sources.

  • Easier testing by decoupling business logic from data storage logic.

Identical Methods in Services and Repositories

• It's common for methods in services to mirror those in repositories:

  • This duplication is intentional and serves specific design purposes.

  • It emphasizes the service's role in handling requests and business rules, even if some underlying mechanics appear redundant.

Conclusion

• Understanding the distinction and cooperation between services and repositories is crucial for effective application architecture in Nest.

• As we progress, setting up our Messages Service and Messages Repository will help solidify these concepts.