Database Migrations

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...

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

Flyway

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

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

Introducing Flyway into your project

3. Tweak/optimise if necessary

4. Run the following command:

./flyway.sh init

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 | |

+-----------------+--------------+------+-----+-------------------+-------+

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.

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

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

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