Get started with Liquibase and Neon

Liquibase is an open-source library for tracking, managing, and applying database schema changes. To learn more about Liquibase, refer to the Liquibase documentation.

This guide steps you through installing the Liquibase CLI, configuring Liquibase to connect to a Neon database, deploying a database schema change, and rolling back the schema change. The guide follows the setup described in the Liquibase Get Started.

Prerequisites

A Neon account. See Sign up.
A Neon project. See Create your first project.
Liquibase requires Java. For Liquibase Java requirements, see Requirements. To check if you have Java installed, run java --version, or java -version on macOS`.

Download and extract Liquibase

Download the Liquibase CLI from https://www.liquibase.com/download.

Extract the Liquibase files. For example:

cd ~/Downloads
mkdir ~/liquibase
tar -xzvf liquibase-x.yy.z.tar.gz -C ~/liquibase/

Open a command prompt to view the contents of your Liquibase installation:

cd ~/liquibase
ls
ABOUT.txt      GETTING_STARTED.txt  licenses     liquibase.bat
changelog.txt  internal             LICENSE.txt  README.txt
examples       lib                  liquibase    UNINSTALL.txt

Set your path variable

Add the Liquibase directory to your PATH so that you can run Liquibase commands from any location.

bashrc

profile

zsh

echo 'export PATH=$PATH:/path/to/liquibase' >> ~/.bashrc
source ~/.bashrc

Verify your installation

Verify that the Liquibase installation was successful by running the following command:

liquibase --version
...
Liquibase Version: x.yy.z
Liquibase Open Source x.yy.z by Liquibase

Prepare a Neon database

For demonstration purposes, create a blog database in Neon with two tables, posts and authors.

Open the Neon Console.
Select your project.
Select Databases from the sidebar and create a database named blog. For instructions, see Create a database.

Using the Neon SQL Editor, add the following tables:

-- Creating the `authors` table
CREATE TABLE authors (
    author_id SERIAL PRIMARY KEY,
    first_name VARCHAR(100),
    last_name VARCHAR(100),
    email VARCHAR(255) UNIQUE NOT NULL,
    bio TEXT
);

-- Creating the `posts` table
CREATE TABLE posts (
    post_id SERIAL PRIMARY KEY,
    author_id INTEGER REFERENCES authors(author_id),
    title VARCHAR(255) NOT NULL,
    content TEXT,
    published_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Retrieve your Neon database connection string

From the Neon Dashboard, retrieve your password and a Java connection string from the Connection Details widget. Use the selection drop-down menu.

Your Java connection string should look something like the one shown below.

jdbc:postgresql://ep-cool-darkness-123456.us-east-2.aws.neon.tech/blog?user=alex&password=AbC123dEf

Connect from Liquibase to your Neon database

Create a directory for your Liquibase project. For example:
```
mkdir blogdb
```
Change to your project directory and create a liquibase.properties file.
```
cd blogdb
touch liquibase.properties
```
Open the the liquibase.properties file in an editor and add entries for a liquibase changelog file and your database url. We'll call the changelog file dbchangelog.xml. You will use this file to define schema changes. For the url, specify the Neon connection string you retrieved previously.
```
changeLogFile:dbchangelog.xml  
url: jdbc:postgresql://ep-floral-poetry-66238369.us-east-2.aws.neon.tech/blog?user=alex&password=4GfNAqycba8P&sslmode=require
```

Take a snapshot of your database

In this step, you will run the generateChangelog command in your project directory to create a changelog file with the current state of your database. We'll call this file mydatabase_changelog.xml.

liquibase --changeLogFile=mydatabase_changelog.xml generateChangeLog

You’ll get a changelog file for your database that looks something like this:

<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog" xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext" xmlns:pro="http://www.liquibase.org/xml/ns/pro" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-latest.xsd http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
    <changeSet author="alex (generated)" id="1697969580160-1">
        <createTable tableName="authors">
            <column autoIncrement="true" name="author_id" type="INTEGER">
                <constraints nullable="false" primaryKey="true" primaryKeyName="authors_pkey"/>
            </column>
            <column name="first_name" type="VARCHAR(100)"/>
            <column name="last_name" type="VARCHAR(100)"/>
            <column name="email" type="VARCHAR(255)">
                <constraints nullable="false"/>
            </column>
            <column name="bio" type="TEXT"/>
        </createTable>
    </changeSet>
    <changeSet author="alex (generated)" id="1697969580160-2">
        <createTable tableName="posts">
            <column autoIncrement="true" name="post_id" type="INTEGER">
                <constraints nullable="false" primaryKey="true" primaryKeyName="posts_pkey"/>
            </column>
            <column name="author_id" type="INTEGER"/>
            <column name="title" type="VARCHAR(255)">
                <constraints nullable="false"/>
            </column>
            <column name="content" type="TEXT"/>
            <column defaultValueComputed="CURRENT_TIMESTAMP" name="published_date" type="TIMESTAMP WITHOUT TIME ZONE"/>
        </createTable>
    </changeSet>
    <changeSet author="alex (generated)" id="1697969580160-3">
        <addUniqueConstraint columnNames="email" constraintName="authors_email_key" tableName="authors"/>
    </changeSet>
    <changeSet author="alex (generated)" id="1697969580160-4">
        <addForeignKeyConstraint baseColumnNames="author_id" baseTableName="posts" constraintName="posts_author_id_fkey" deferrable="false" initiallyDeferred="false" onDelete="NO ACTION" onUpdate="NO ACTION" referencedColumnNames="author_id" referencedTableName="authors" validate="true"/>
    </changeSet>
</databaseChangeLog>

Create a schema change

Now, you can start making database schema changes by creating changesets and adding them to the database changelog file you defined in your liquibase.properties file. A changeset is the basic unit of change in Liquibase.

Create the changelog file where you will add your schema changes:
```
cd ~/blogdb
touch dbchangelog.xml
```

Add the following changeset, which adds a comments table to your database. Replace author="alex" id="myIDNumber1234" with your auther name and id, which you can retrieve from your changelog file, described in the previous step.

<?xml version="1.0" encoding="UTF-8"?>  
<databaseChangeLog  
xmlns="http://www.liquibase.org/xml/ns/dbchangelog"  
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
xmlns:pro="http://www.liquibase.org/xml/ns/pro"  
xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-4.4.xsd
    http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-4.5.xsd">
    <changeSet author="alex" id="myIDNumber1234">
        <createTable tableName="comments">
            <column autoIncrement="true" name="comment_id" type="INTEGER">
                <constraints nullable="false" primaryKey="true" primaryKeyName="comments_pkey"/>
            </column>
            <column name="post_id" type="INTEGER">
                <constraints nullable="false" foreignKeyName="fk_comments_post_id" referencedTableName="posts" referencedColumnNames="post_id"/>
            </column>
            <column name="author_id" type="INTEGER">
                <constraints nullable="false" foreignKeyName="fk_comments_author_id" referencedTableName="authors" referencedColumnNames="author_id"/>
            </column>
            <column name="comment" type="TEXT"/>
            <column name="commented_date" type="TIMESTAMP" defaultValueComputed="CURRENT_TIMESTAMP"/>
        </createTable>
    </changeSet>
</databaseChangeLog>

Deploy your change

Deploy your database schema change by running the update command:

liquibase update

Command output

If the command was successful, you’ll see output similar to the following:

Starting Liquibase at 07:33:53 (version 4.24.0 #14062 built at 2023-09-28 12:18+0000)
Liquibase Version: 4.24.0
Liquibase Open Source 4.24.0 by Liquibase
Running Changeset: dbchangelog.xml::myIDNumber1234::AlexL

UPDATE SUMMARY
Run:                          1
Previously run:               0
Filtered out:                 0
-------------------------------
Total change sets:            1

Liquibase: Update has been successful. Rows affected: 1
Liquibase command 'update' was executed successfully.

info

When you run a changeset for the first time, Liquibase automatically creates two tracking tables in your database:

databasechangelog: Tracks which changesets have been run.
databasechangeloglock: Ensures only one instance of Liquibase runs at a time.

You can verify these tables were created by viewing the blog database on the Tables page in the Neon Console. Select Tables from the sidebar.

Rollback a change

Try rolling back your last change by running the Liquibase rollbackCount command:

liquibase rollbackCount 1