example2

Pre-Liquibase example application

Example application Medusa showcases how the Pre-Liquibase module might be used for a Spring Boot based application which uses multiple data sources.

Like Example 1, the aim of Pre-Liquibase in this application is to ensure that a database "home" (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 by schema.

Since the application uses multiple datasources it cannot use auto-configuration in the traditional sense (see Example1). Therefore, most beans must be configured manually.

This example application uses

• Spring Boot 3

• Spring Data JPA (Hibernate) - with multiple data sources

• Liquibase

With the example we’ve achieved:

• We are using Pre-Liquibase and Liquibase with multiple data sources.

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

• Like in Example 1, the schema names are dynamic. Schema 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 schemas will be auto-created with a name of 'medusa_uat3_xxx' (where 'xxx' corresponds to a descriptive name of our datasource). 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.

Beans configuration

Since we are using multiple data sources in the application we cannot rely on Spring Boot’s auto-configuration. Instead this must be done manually.

All beans wiring take place in MedusaApplicationConfig class. The configuration to a great extend mimics what Spring Boot would be doing automatically had we only had one data source.

The important things to note are:

• PreLiquibase bean must be configured as shown in the config class. Do not forget the execute().

• There is a certain order in which things need to happen. This is achieved by Spring’s @DependsOn annotation. The order is:

  1. Creation of DataSource

  2. Pre-Liquibase execution

  3. Liquibase execution

  4. Creation of JPA stuff

The beans configuration is created such that all configuration properties are available under the persistence. namespace with the following sub-namespaces:

• persistence.datasource.dbX.. DataSource configuration properties, such as url, username and password. If these are not specified then Spring Boot will use an embedded H2 database.

• persistence.datasource.poolconfig.dbX.. JDBC Connection Pool properties. These are forwarded as-is to whatever connection pool implementation is in use, e.g. Hikari.

• persistence.preliquibase.dbX.. Pre-Liquibase properties. In an multi-datasource application it will likely be required to set sqlScriptReferences.

• persistence.liquibase.dbX.. Liquibase properties.

• persistence.jpa.dbX.. Spring JPA properties. You can use all the standard ones plus in addition persistenceUnitName for giving the JPA Persistence Unit bean a custom name.

• persistence.jpa.dbX.properties.. JPA Provider properties. These are forwarded as-is to whatever JAP Provider is in use, e.g. Hibernate.

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 and log level was INFO)

(001) n.l.s.p.example.MedusaApplication        : Starting MedusaApplication using Java 11.0.14 on ....
(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 33 ms. Found 1 JPA repository interfaces.
(005) .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
(006) .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 9 ms. Found 2 JPA repository interfaces.
(007) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-app - Starting...
(008) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-app - Start completed.
(009) n.l.s.preliquibase.PreLiquibase          : PreLiquibase: Executing SQL script : class path resource [preliquibase/db1/h2.sql]
(010) liquibase.lockservice                    : Successfully acquired change log lock
(011) liquibase.changelog                      : Creating database history table with name: medusa_uat9_app.LIQUIBASE_DBCHANGELOG
(012) liquibase.changelog                      : Reading from medusa_uat9_app.LIQUIBASE_DBCHANGELOG
(013) liquibase.changelog                      : Table PERSONS created
(014) liquibase.changelog                      : Primary key added to PERSONS (PERSON_ID)
(015) liquibase.changelog                      : ChangeSet /liquibase/db1/changelog/db.changelog_schema_1.0.0.yaml::1.0.0::lbruun ran successfully in 16ms
(016) liquibase.lockservice                    : Successfully released change log lock
(017) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-log - Starting...
(018) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-log - Start completed.
(019) n.l.s.preliquibase.PreLiquibase          : PreLiquibase: Executing SQL script : class path resource [preliquibase/db2/h2.sql]
(020) liquibase.lockservice                    : Successfully acquired change log lock
(021) liquibase.changelog                      : Creating database history table with name: medusa_uat9_log.LIQUIBASE_DBCHANGELOG
(022) liquibase.changelog                      : Reading from medusa_uat9_log.LIQUIBASE_DBCHANGELOG
(023) liquibase.changelog                      : Table APP_EVENTS created
(024) liquibase.changelog                      : Primary key added to APP_EVENTS (APP_EVENT_ID)
(025) liquibase.changelog                      : Table LAST_LOGINS created
(026) liquibase.changelog                      : Primary key added to LAST_LOGINS (LAST_LOGIN_USERNAME)
(027) liquibase.changelog                      : ChangeSet /liquibase/db2/changelog/db.changelog_schema_1.0.0.yaml::1.0.0::lbruun ran successfully in 16ms
(028) liquibase.lockservice                    : Successfully released change log lock
(029) o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: app]
(030) org.hibernate.Version                    : HHH000412: Hibernate ORM core version 5.6.4.Final
(031) o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
(032) org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
(033) o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
(034) j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'app'
(035) o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: log]
(036) org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
(037) o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
(038) j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'log'
(039) n.l.s.p.example.MedusaApplication        : Medusa environment name: uat9
(040) n.l.s.p.example.MedusaApplication        : Started MedusaApplication in 4.383 seconds (JVM running for 4.792)
  example output removed
(041) j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'log'
(042) j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'app'
(043) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-log - Shutdown initiated...
(044) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-log - Shutdown completed.
(045) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-app - Shutdown initiated...
(046) com.zaxxer.hikari.HikariDataSource       : JDBCConnectionPool-app - Shutdown completed.

Line 7-8 is Hikari startup for 'db1' (display name 'app')
Line 9 is Pre-Liquibase execution for 'db1'
Line 10-16 is Liquibase exectionn for 'db1'
Line 17-18 is Hikari startup for 'db2' (display name 'log')
Line 19 is Pre-Liquibase execution for 'db2'
Line 20-28 is Liquibase exectionn for 'db2'
Line 29-34 is Spring JPA / Hibernate initialization for 'db1' (display name 'app')
Line 35-38 is Spring JPA / Hibernate initialization for 'db2' (display name 'log')
Line 41 is Spring JPA closedown for 'db1' (display name 'app')
Line 42 is Spring JPA closedown for 'db2' (display name 'log')
Line 43-44 is Hikari closedown for 'db1' (display name 'app')
Line 45-46 is Hikari closedown for 'db2' (display name 'log')