Managing Database

Liquibase is an open source (Apache License), database-independent management library with a database-backed version control system.

Liquibase tracks all database changes in one or more changelogs. Each changelog contains one or more changesets. Each changeset describes the changes that need to be applied to the database in a database independent manner. As Liquibase applies the changeset to your database, it writes a row in a DATABASECHANGELOG table indicating the changeset is applied. On subsequent executions, Liquibase compares the changesets in the changelog with the ones stored in DATABASECHANGELOG. If a changeset has already been applied, Liquibase will not reapply the change and will not add a new entry in DATABASECHANGELOG.

Liquibase creates a checksum for each changeset. Once you have applied a changeset to a database, it must not be edited in the changelog or Liquibase will require you to resolve the checksum mismatch.

For more information, see the Liquibase Manual.

Data Population with Liquibase

Elastic Path projects use a combination of Liquibase scripts and Import/Export data to populate the commerce database.

The Data Population Tool provides a unified mechanism to create new databases or update existing databases. It uses Liquibase to manage the execution of both Liquibase scripts and Import/Export data by wrapping each Import/Export data set in a Liquibase change set. This has a number of benefits:

• Import/Export updates are applied only once to the database, unless configured otherwise

• Using Liquibase contexts, Import/Export data sets can be applied only to specific environments

  For example, the test data that shouldn’t go to production.

• Property placeholders can be defined in both Liquibase and Import/Export data

  These placeholders are filtered at run time using an external properties file to support populating environment-specific values

Change Log Locations

The following changelogs are executed when you populate the database:

extensions/database/ext-data/src/main/resources/schema/schema-initializer-changelog.xml
    commerce-engine/liquibase/core-schema/src/main/resources/elasticpath-db-changelog.xml
        commerce-engine/liquibase/core-schema/src/main/resources/core-changelog-master.xml
            <includes all core changelogs>
    extensions/database/ext-data/src/main/resources/schema/schema-customizations-changelog.xml
extensions/database/ext-data/src/main/resources/data/liquibase-changelog.xml
    <includes all extensions data changelogs>

Generating Database Schema Documents

Using SchemaSpy, a Java-based command-line interface tool, you can generate database schema documents from your database.

Before you start

You must have Graphviz installed on your machine. Graphviz is required in the generation of the table/view relationships graph.

To generate your database schema documents:

1. Open the command prompt and navigate to extensions/database/ext-schema-documentation

2. Execute the command below to run Maven’s site plugin and generate the documentation.

   mvn site
   

3. Navigate to extensions/database/ext-schema-documentation/target/site/schemaspy

4. Open index.html in a web browser to view the schema documents