example1

Pre-Liquibase example application

Example application Medusa showcases how the Pre-Liquibase module might be used for a Spring Boot based application. The aim of Pre-Liquibase in this application is to ensure that a database "home" (a catalog or a schema) exists for the current instance of the application. This way multiple instances of the application can all use the same database server and the same database identity, yet inside the database server the various instances are duly separated.

The example application uses

• Spring Boot 3

• Spring Data JPA (Hibernate)

• Liquibase

With the example we’ve achieved:

• The Pre-Liquibase module ensures that the schema where tables live (including the two Liquibase metadata tables) actually exist prior to executing Liquibase itself.

• The schema name is dynamic. It takes its name partly from an OS environment variable, MEDUSA_ENVNAME, so that different instances of the Medusa application can use the same database user, albeit they will be separated by schema name. This way, when a new instance (a new environment) of the Medusa application is created, say 'uat3', the schema will be auto-created with a name of 'medusa_uat3'. All we have to do is to make sure that different Medusa environments have different value in the OS environment variable MEDUSA_ENVNAME. Such way of working fits nicely with the cloud world: different instances of our application (of the same version) deployed as different environment should not differ in what gets deployed. They should only differ in their environment. The alternative is that our source code repo will have environment specific information in it. That is rarely a good idea.

The project validates the Spring Environment properties, in particular medusa.envName, on startup. You certainly don’t have to do that. It is merely meant as an example of how to validate Spring properties which come from a source you don’t fully expect to always comply with the application’s requirements (meaning an operator may have misconfigured something).

Running the application

When the application is executed you should see the following log output:
(for this execution the content of the OS environment variable MEDUSA_ENVNAME was uat9)

(001) n.l.s.p.example.MedusaApplication        : Starting MedusaApplication using Java [...]
(002) n.l.s.p.example.MedusaApplication        : No active profile set, falling back to default profiles: default
(003) .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
(004) .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 36 ms. Found 1 JPA repository interfaces.
(005) com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
(006) com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
(007) n.l.s.preliquibase.PreLiquibase          : PreLiquibase: Executing SQL script : URL [jar:file:/trials/preliquibase-spring-boot-example-1.0.0.jar!/BOOT-INF/classes!/preliquibase/h2.sql]
(008) l.lockservice.StandardLockService        : Successfully acquired change log lock
(009) l.c.StandardChangeLogHistoryService      : Creating database history table with name: medusa_uat9.DATABASECHANGELOG
(010) l.c.StandardChangeLogHistoryService      : Reading from medusa_uat9.DATABASECHANGELOG
(011) liquibase.changelog.ChangeSet            : Table PERSONS created
(012) liquibase.changelog.ChangeSet            : Primary key added to PERSONS (PERSON_ID)
(013) liquibase.changelog.ChangeSet            : ChangeSet classpath:/db/changelog/db.changelog_schema_1.0.0.yaml::1.0.0::lbruun ran successfully in 2ms
(014) l.lockservice.StandardLockService        : Successfully released change log lock
(015) o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
(016) org.hibernate.Version                    : HHH000412: Hibernate ORM core version 5.4.27.Final
(017) o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
(018) org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
(019) o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
...

Line 7 is Pre-Liquibase being executed.
Lines 8-14 is Liquibase itself.
Lines 15-19 is Hibernate initialization.