Database migrations with Flyway

1. Database Migrations

2. What's the problem?
Provide upgrades of applications and databases to our
customers
Some customers require SQL scripts to run via DB admin
tools, e.g. Oracle (sqlplus)
We don't have database schemas that reflect what's been
applied in terms of updates - always the newest
We don't really understand what Hibernate is doing to
create/modify tables based on our persistent objects, we
rely on it for optimization, indexes etc...

3. Database Migrations
Structure SQL scripts for creation of the
schema, updates of the schema accordingly
Use a tool to run these migrations:
● In a specific order
● Against a specific database (MySQL,
Oracle)
● Recording the actions in a schema version
table
Lots of tools that do this

4. Flyway
Allows us to do migrations:
● From a shell script
● Programmatically
● When Spring starts
● Using Maven as a build tool

5. Introducing Flyway into your project
Has been done for MIF - there's a dbtool folder
in the source structure. We can provide a
template in SVN that can be used.
1. Download the dbtool structure
2. Generate an export of the schema that
Hibernate has created for your project

6. Introducing Flyway into your project
3. Tweak/optimise if necessary
4. Run the following command:
./flyway.sh init

7. Introducing Flyway into your project
This creates the SCHEMA_VERSION table:
mysql> desc SCHEMA_VERSION;
+-----------------+--------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+--------------+------+-----+-------------------+-------+
| version | varchar(20) | NO | PRI | NULL | |
| description | varchar(100) | YES | | NULL | |
| type | varchar(10) | NO | | NULL | |
| script | varchar(200) | NO | UNI | NULL | |
| checksum | int(11) | YES | | NULL | |
| installed_by | varchar(30) | NO | | NULL | |
| installed_on | timestamp | NO | | CURRENT_TIMESTAMP | |
| execution_time | int(11) | YES | | NULL | |
| state | varchar(15) | NO | | NULL | |
| current_version | tinyint(1) | NO | MUL | NULL | |
+-----------------+--------------+------+-----+-------------------+-------+

8. Performing a migration
Assume you've added a new script in the
<dbname>/sql folder of dbtool
Run:
./flyway.sh migrate
This will run the script and record the action in
the SCHEMA_VERSION table.

9. Flyway dbtool structure
├── mysql
│ ├── conf
│ │ └── flyway.properties
│ ├── flyway.cmd
│ ├── flyway.sh
│ ├── jars
│ │ └── mysql-connector-java-5.1.14.jar
│ └── sql
│ ├── V1__MIFBaseSchema.sql
│ └── V2__JOB.DATE_ACKNOWLEDGED.sql
└── oracle
├── conf
│ └── flyway.properties
├── flyway.cmd
├── flyway.sh
├── jars
│ └── ojdbc14-10.2.0.5.jar
└── sql

10. Process Change
Need to change the way we develop persistent
objects with Hibernate
As well as changing an object we also need to
provide a migration script (and a rollback script)
Put it in the <dbname>/sql folder.
ls -Al mysql/sql
V1__MIFBaseSchema.sql
V2__JOB.DATE_ACKNOWLEDGED.sql

11. Example
Change a persistent object to add a new field
Write a script with the appropriate ALTER
TABLE ADD COLUMN statement.
Write the rollback script
Test