Liquibase is a tool that helps manage database schema changes. It improves on older manual processes by keeping changes in source control, only applying new changes, and providing automatic rollback. Each change is added as a changeset in a changelog file in a database-agnostic format like JSON or XML. Liquibase then handles applying the changes and rolling back if needed. This avoids many errors from the manual process while keeping changes version controlled.

1. LIQUIDATING DATABASE
FRUSTRATIONS WITH
LIQUIBASE
Paul Churchward, FRM
September 23, 2016

2. THE OLD WAY
OF MANAGING DATABASE
CHANGES

3.  Database schema & reference data changes are applied manually to
each environment
local > DEV > SIT > PRE-PROD > PROD > DR
 SIT, and other production-like environments managed by DBA
 Nothing is kept in source control
 Highly manual. Highly error prone.

4. THE (SLIGHTLY BETTER) OLD WAY

5.  1 script per DB change
 Additional scripts for roll-back
 Scripts kept in source control
 Change existing scripts multiple times until they're right
 Scripts are applied manually to each environment
 SIT, and other production-like environments managed by DBA
 Still very manual. Still very error prone.
 Lots and lots of scripts
 Must keep track of the order of the scripts!
 Must keep track of which scripts to run on which deploys!

6. THE LIQUIBASE WAY

7. LIQUIBASE UPDATES THE DB
… NOT YOU
(MOST OF THE TIME)

8.  Each database schema & reference data change is added to source control
> developer choses how to organize them.
Examples:
One change log file per feature
One change log file
 Liquibase only executes new changes since last run
 Changes can be specified in database agnostic formats (XML, JSON) or SQL
 No merge conflicts.
 Never modify an existing change, always create a new one.
 Automatic rollback without a custom script (unless you want one)
 No more manual upgrades

9. EXAMPLE

10. A sample JSON changelog file
Each DB changes is added to a changeset, and
multiple change sets are added to a
changelog.
Each changeset has an author ID and an ID
that is unique to that author within the
changelog file
This create table change could have been
expressed in XML (also DB agnostic) or in
plain SQL with metadata in SQL comments
A project can support any number of
changelog files
Always create a new changeset, never alter an
existing one (except for stored procedures
and then use runOnChange attribute)
{
"databaseChangeLog": [
{
"changeSet": {
"id": "1",
"author": "Foo",
"changes": [
{
"createTable": {
"tableName": "person",
"columns": [
{
"column": {
"name": "id",
"type": "int",
"autoIncrement": true,
"constraints": {
"primaryKey": true,
"nullable": false
},
}
},
{
"column": {
"name": "firstname",
"type": "varchar(50)"
}
},
{
"column": {
"name": "lastname",
"type": "varchar(50)",
"constraints": {
"nullable": false
}
}
}
…

11. A sample SQL changelog file
SQL changesets are DBMS platform
dependent unlike XML and JSON formats
that are converted into platform
dependent SQL
Metadata is defined in SQL comments
Must provide your own rollback scripts
--liquibase formatted sql
--changeset Foo:1
create table test1 (
id int primary key,
name varchar(255)
);
--rollback drop table test1;
--changeset Foo:2
insert into test1 (id, name) values (1, ‘name 1′);
insert into test1 (id, name) values (2, ‘name 2′);
--changeset Foo:3 dbms:oracle
create sequence seq_test;

12. RUNNING LIQUIBASE

13. Automatically
On Web App
Startup
Continuous
Integration
Job via
Maven Goal
Liquibase
commandline
Liquibase
generated
SQL delta
script
Ideal for paranoid DBAs

14.  Automatically on web app startup
> Depend on liquibase-core artifact
> Add a servlet listener
 Run from Maven via plugin:
 Run from Liquibase jar
> Download from liquibase.org
<dependency>
<groupId>org.liquibase</groupId>
<artifactId>liquibase-maven-plugin</artifactId>
<version>3.5.2</version>
</dependency>
<dependency>
<groupId>org.liquibase</groupId>
<artifactId>liquibase-core</artifactId>
<version>3.5.2</version>
</dependency>

15. ROLLBACK

16.  Rolling back changes is only possible with Maven or Liquibase commandline
 Provide count of changesets to rollback or a liquibase database tag
 Rolling back and creating a checkpoint
 Rolling back to a previous checkpoint
mvn liquibase:rollback -Dliquibase.rollbackCount=3
mvn liquibase:rollback -Dliquibase.rollbackCount=3
mvn liquibase:tag -Dliquibase.tag=checkpoint
mvn liquibase:rollbackSQL -Dliquibase.rollbackTag=checkpoint