Simple Program

In this section, we first explain the basic usage of ldbc by creating and executing a simple program.

※ The program environment used here is assumed to be the one built in the setup.

The first program

In this program, we will create a program that connects to a database and retrieves the results of a calculation.

Now, let's create a query that asks the database to calculate a constant using sql string interpolator.

val program: Executor[IO, Option[Int]] = sql"SELECT 2".query[Int].to[Option]

Queries created with sql string interpolator use the query method to determine the type to retrieve. Here, query[Int] is used to get the Int type. Also, the to method determines the type to retrieve. Here, to[Option] is used to get the Option type.

Finally, write a program that connects to the database and returns a value. This program connects to the database, executes the query, and retrieves the results.

connection
  .use { conn =>
    program.readOnly(conn).map(println(_))
  }
  .unsafeRunSync()

Connected to database to calculate constants. Quite impressive.

Execute with Scala CLI

This program can also be run using the Scala CLI. The following command will execute this program.

scala-cli https://github.com/takapi327/ldbc/tree/master/docs/src/main/scala/02-Program.scala --dependency io.github.takapi327::ldbc-dsl:0.3.0-beta8 --dependency io.github.takapi327::ldbc-connector:0.3.0-beta8

Second program

What if you want to do multiple things in one transaction? Easy! Since Executor is a monad, you can use for comprehensions to make two small programs into one big program.

val program: Executor[IO, (List[Int], Option[Int], Int)] =
  for
    result1 <- sql"SELECT 1".query[Int].to[List]
    result2 <- sql"SELECT 2".query[Int].to[Option]
    result3 <- sql"SELECT 3".query[Int].unsafe
  yield (result1, result2, result3)

Finally, write a program that connects to the database and returns a value. This program connects to the database, executes the query, and retrieves the results.

connection
  .use { conn =>
    program.readOnly(conn).map(println(_))
  }
  .unsafeRunSync()

Run with Scala CLI.

This program can also be run using the Scala CLI. The following command will execute this program.

scala-cli https://github.com/takapi327/ldbc/tree/master/docs/src/main/scala/03-Program.scala --dependency io.github.takapi327::ldbc-dsl:0.3.0-beta8 --dependency io.github.takapi327::ldbc-connector:0.3.0-beta8

Third program

Let's write a program that writes to a database. Here, we connect to the database, execute a query, and insert data.

val program: Executor[IO, Int] =
  sql"INSERT INTO user (name, email) VALUES ('Carol', 'carol@example.com')".update

The difference from the previous step is that the commit method is called. This commits the transaction and inserts the data into the database.

connection
  .use { conn =>
    program.commit(conn).map(println(_))
  }
  .unsafeRunSync()

Execute with Scala CLI.

This program can also be run using the Scala CLI. The following command will execute this program.

scala-cli https://github.com/takapi327/ldbc/tree/master/docs/src/main/scala/04-Program.scala --dependency io.github.takapi327::ldbc-dsl:0.3.0-beta8 --dependency io.github.takapi327::ldbc-connector:0.3.0-beta8