Scala/ZIO 2.x: Postgres/Slick/Tapir/zio-http Example

This example illustrates use of:

• Postgres database and Slick for data access
• Tapir/zio-http for building the underlying REST API with Swagger UI.

As Slick does not provide support for ZIO, zio-slick-interop is used to ensure a bottom-up use of zio as far as possible.

This example also:

• Leverages the ZIO dependencies injection pattern ZLayer (IoC)
• Provides some database integration tests by combining zio-test and test-container
• Use zio-prelude ZValidation to ensure that data model objects are always clean and validated

References

• ZIO
• Introduction to Dependency injection in ZIO
• ZIO validation with ZValidation from zio Prelude
• Introduction to ZIO Test
• Provides idiomatic, easy-to-use ZLayers for Testcontainers-scala
• Slick library for Scala
• zio-slick-interop, small library, that provides interop between Slick and ZIO
• Introduction to ZIO http
• Tapir, running as a zio-http server

Running a Postgres docker container and running the example

Before running the example and/or tests, you need a Postgres image and a running container:

$ docker run -d --name zio-example-postgres -p 5432:5432 -e POSTGRES_PASSWORD=password postgres

Pay attention to the configuration file settings to correctly address the postgres container:

example = {
    driver = "org.postgresql.Driver",
    url = "jdbc:postgresql://localhost:5432/postgres",
    user = "postgres",
    password = "password",
    connectionPool = disabled
}

To run the example, type $ sbt run

The data model

The object data model resides in the model package. This quite dummy model is composed by two tables: User and Post.

User

Field	Data type	Description	Constraint
login	String	id of a user	Primary key, Not empty, Length must be upper or equal than 6
email	String	Email of the user	Not Null, Must be a valid email

Post

Field	Data type	Description	Constraint
id	Long	id of a post	Primary key
dateOfIssue	Instant	Date of issue	Not Null
userLogin	String	The user who issued the post	Foreign key (User)
message	String	The message	Not Null, Not empty

Http server

This example provides a simple REST API for managing users and posts, based on zio-http. As currently this library is not yet available within the official dev.zio ecosystem, the maven version is used ([email protected]). Hope [email protected] will be soon available and would provide test server features. This example leverages tapir capabilities for swagger docs and UI. Try http://localhost:8080/docs/ to get the swagger UI.