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https://github.com/lastland/scala-forklift-quill

A demonstration of using Scala-Forklift to support database migrations on Quill.
https://github.com/lastland/scala-forklift-quill

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A demonstration of using Scala-Forklift to support database migrations on Quill.

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README 

        
This is a simple demonstration of using [Scala-Forklift](https://github.com/lastland/scala-forklift) to support database migrations on [Quill](https://github.com/getquill/quill). This demo still contains some hard code and unimplemented features, but it's sufficient to show how it works.



## How to Use



*Note* : Don't directly compile the project in your `sbt`. If you haven't run any of the commands listed below, it will fail.



Clone this repo. Edit the database configuration in `app/src/main/resources/application.conf` to your database settings. Once it's done, enter `sbt` in the project root. Type the following command in your sbt:



    > mg init

    [info] Running MyMigrations init

    [success] Total time: 1 s, completed



Then find the code in `migrations/src/main/scala/Migrations.scala`, uncomment the following code:



    case class Migrations(id: Int)

    lazy val lookupMigration = quote {

        query[Migrations].map(_.id)

    }

    lazy val applyMigration = quote {

        (id: Int) => query[Migrations].insert(_.id -> id)

    }



    override def alreadyAppliedIds = {

        db.run(lookupMigration)

    }



    def latest =

        if (alreadyAppliedIds.isEmpty) None

        else Some(alreadyAppliedIds.last)



    override protected def up(migrations: Iterator[Migration[Int, Unit]]) {

        for (m <- migrations) {

            m.up

            db.run(applyMigration).using(List(m.id))

        }

    }



And comment out the following code:



    override def alreadyAppliedIds = List()



Back to your sbt, enter the following command:



    > mg update

    [info] Running MyMigrations update

    create link to ./migrations/src/main/scala/migrations/1.scala for /path-to-quill-example/./migrations/src_migrations/main/scala/1.scala

    [success] Total time: 0 s, completed

    > mg apply

    [info] Compiling 2 Scala sources to /path-to-quill-example/migrations/target/scala-2.11/classes...

    [info] Running MyMigrations apply

    applying migrations: 1

    [success] Total time: 1 s, completed



This will execute the migration defined in `migrations/src_migrations/main/scala/1.scala`:



    db.execute("create table `users` (`id` integer not null primary key, `name` varchar(255) not null)"))



Once the `users` table is created, you can run the application code:



    > app/run

    [info] Running Application

    List()

    [success] Total time: 0 s, completed



To add some data into this list, we need to execute the next migration defined in `migrations/src_migrations/main/scala/2.scala`:



    val insert = quote {

        (id: Int, name: String) => query[Users].insert(_.id -> id, _.name -> name)

    }

    db.run(insert).using(List((1, "Harry Potter"),

        (2, "Ron Weasley"), (3, "Hermione Granger")))



Apply the migration in your sbt:



    > mg update

    [info] Running MyMigrations update

    create link to ./migrations/src/main/scala/migrations/2.scala for /path-to-quill-example/./migrations/src_migrations/main/scala/2.scala

    [success] Total time: 0 s, completed

    > mg apply

    [info] Compiling 2 Scala sources to /path-to-quill-example/migrations/target/scala-2.11/classes...

    [info] /path-to-quill-example/migrations/src/main/scala/migrations/2.scala:12: INSERT INTO users (id,name) VALUES (?, ?)

    [info]       db.run(insert).using(List((1, "Harry Potter"),

    [info]             ^

    [info] Running MyMigrations apply

    applying migrations: 2

    [success] Total time: 2 s, completed



Then checkout the application:



    > app/run

    [info] Running Application

    List(Harry Potter, Ron Weasley, Hermione Granger)

    [success] Total time: 0 s, completde



## Challenges



Different with Slick, Quill uses probes to check if a database schema matches the Scala queries at compile time. This is why some code fragments in `Migrations.scala` has to be commentted out at first: `migrations` table was not created until `mg init` was executed.



This may not be a problem if this part of code was in the library, because it has already been compiled. However, this will still cause troubles when users want to extend the library.



## Others



For more information on Scala-Forklift, please refer to https://github.com/lastland/scala-forklift. A more detailed example of using Slick can be found here: https://github.com/lastland/scala-forklift/tree/develop/example