# Spring Boot with DB Migration (1 of 2)

Here, I write how to build application in Spring Boot with DB Migration. I use Kotlin and Harmonica, Kotlin database migration library.

## Environment

• Kotlin 1.3.20
• Spring Boot 2.1.2
• Harmonica 1.1.17
• PostgreSQL
• IntelliJ IDEA
• JDK 11 (You can use JDK 8 or later)

## Prepare Application Base

First, let’s generate application base on Spring Initializr.

Choose the following component.

• Kotlin
• Spring Boot 2.1.2

Leave the project meta data as it is.

• Web
• PostgreSQL
• JPA
• Thymeleaf

In old articles, I used kotlinx.html for template, but this time I use Thymeleaf, because most people are familiar with it.

Click “Generate Project” button and extract the zip file, then you can see the file structure as follows.

## Prepare PostgreSQL

Here is the database configuration.

If you don’t have PostgreSQL, you can prepare it with docker as follows.

If you want to change the listening port, please change the first 5432 to another port number.

## Open the Project in IntelliJ IDEA

From the “File” menu, click “Open”, and choose the file, “settings.gradle“. You will see the dialog that asks whether you open it as a project or not. Then, please click “Open as a Project” button.

After that you will see the dialog for importing, then configure it and click “OK” button.

Well, let’s change the Kotlin version. Open build.gradle and change Kotlin version to 1.3.20.

## Migration

Let’s add the module. In the Project tool window, choose top directory. From the “File” menu, select “New” and “Module”, the you’ll see “New Module” dialog. On the dialog, please choose “Gradle” in the left pane, and choose “Kotlin (Java)” in the right pane, and click “Next” button.

Next, please configure as follows, and click “Next” button and add the module.

Auto syncronization will work and you may get the following error output.

Now, open db/build.gradle and remove the version of the Kotlin plugin and add libraries.

### Configuration

Set up the db and directory configuration.

Add the next expression to the bottom of build.gradle.

Next, execute the following command.

And create file db/src/main/kotlin/com/example/demo/db/config/Default.kt as follows.

Now, let’s add the migration. Execute the next command.

Then, you can see the file db/src/main/kotlin/com/example/demo/db/migration/Mxxxxxxxxxxxxxxxxxx_CreateTask.kt. Change it as follows.

Execute migration as follows.

You can see the output like follows.

### See the Database

Let’s see the database with psql.

harmonica_migration table contains the executed migration versions. task table is what we wanted to create and task_id_seq sequence is the sequence for task table, which is created automatically.

task table has id column, which is added automatically, and it uses the sequence.

This article continues to Spring Boot with DB Migration (2 of 2).