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DataSource Initialization

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Andy Wilkinson edited this page Jan 29, 2021 · 3 revisions

Boot’s current behaviour

  1. when the DataSource is post-processed

    1. if DDL (schema) scripts are available:

      1. they are applied to the DataSource

      2. if DML (data) scripts are available they are applied to the DataSource

  2. when the LocalContainerEntityManagerFactoryBean is post-processed

    1. if Hibernate initialised the schema publish DataSourceSchemaCreatedEvent

  3. when the DataSourceSchemaCreatedEvent is received

    1. if the schema hasn’t been initialised and DML (data) scripts are available they are applied to the DataSource

The presence or absence of DDL (schema) scripts changes when DML (data) scripts are run. When DDL scripts are present, DML scripts are run immediately after the DDL scripts. When there are no DDL scripts, DML scripts are run once Hibernate has created the schema. If Hibernate isn’t being used, DML scripts are never run irrespective of any other component that may have created the schema. If you want to use a DDL script to manage parts of the schema that Hibernate won’t touch, your DML scripts cannot interact with parts of the schema that Hibernate creates as they’ll be run too soon.

The auto-configurations for Flyway and Liquibase create various …DependsOnPostProcessor beans to ensure that JdbcOperations, NamedParameterJdbcOperations, and EntityManagerFactory beans cannot be used until the database has been migrated. There are no …DependsOnPostProcessor beans created for jOOQ. This means that the database may not have been initialized when accessed with jOOQ during application context refresh.

The Hibernate auto-configuration does not create any …DependsOnPostProcessor beans. If there are no DDL scripts – so Hibernate will create the schema and cause DML scripts to be applied – the database may not have been initialised when accessed during application context refresh using anything other than Hibernate.

Hibernate and JPA

Schema creation (DDL)

javax.persistence.schema-generation.create-source controls how the schema is created. Possible values are the following:

  • metadata

  • script

  • metadata-then-script

  • script-then-metadata

These settings allow the schema to be created using:

  • metadata in the persistence unit

  • a user-provided script

  • metadata in the persistence unit and then a user-provided script

  • a user provided script and then the metadata in the persistence unit

javax.persistence.schema-generation.create-script-source is used to provide the script. The default for create-source is metadata if create-script-source is not set or script when it is set. The source can be a Reader instance, otherwise it’s treated as a String (via a call to toString()) and then handled as a URL, or a relative file path, or an absolute file path.

Schema initialization (DML)

javax.persistence.sql-load-script-source is used to provide a script that loads data into the database. The source can be a Reader instance, otherwise it’s treated as a String (via a call to toString()) and then handled as a classpath resources, or a relative file path, or an absolute file path. A source’s presence is optional but a warning is logged when a source is absent.

hibernate.hbm2ddl.import_files is also used to provide a script that loads data into the database. The source can only be loaded as a classpath resource. A resource’s presence is optional and absent resources are silently skipped. The property’s value value is /import.sql.

Schema initialization is only performed if schema creation has been performed.

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