3.3.4. The Execution of Database Scripts by the Server
The mechanism to execute database scripts by the server is used for bringing the DB up to date at the start of the application server and is activated during the initialization of the Middleware block. Obviously, the application should have been built and deployed on the server – production or developer’s Tomcat instance.
Depending on the conditions described below, this mechanism either executes create or update scripts, i.e., it can initialize the DB from scratch and update it. However, unlike the Gradle
createDb task described in the previous section, the database must exist to be initialized – the server does not create the DB automatically but only executes scripts on it.
The mechanism to execute scripts by the server works as follows:
If the DB does not have the
SEC_USERtable, the database is considered empty and the full initialization is run using the create scripts. After executing the initialization scripts, their names are stored in the
SYS_DB_CHANGELOGtable. The names of all available update scripts are stored in the same table, without their execution.
If the DB has the
SEC_USERtable but does not have the
SYS_DB_CHANGELOGtable (this is the case when the described mechanism is launched for the first time on the existing production DB), no scripts are executed. Instead, the
SYS_DB_CHANGELOGtable is created and the names of all currently available create and update scripts are stored.
If the DB has both the
SYS_DB_CHANGELOGtables, the update scripts whose names were not previously stored in the
SYS_DB_CHANGELOGtable are executed and their names are stored in the
SYS_DB_CHANGELOGtable. The sequence of scripts execution is determined by two factors: the priority of the application component (see database scripts directory:
20-bpm, …) and the name of the script file (taking into account the subdirectories of the
updatedirectory) in the alphabetical order.
Before the execution of update scripts, the check is performed, whether all creation scripts of application components have been run (by checking the
SYS_DB_CHANGELOGtable). If the database is not initialized for use of some application component, its creation scripts are executed.
The mechanism to execute the scripts on server startup is enabled by the cuba.automaticDatabaseUpdate application property.
In already running application, the script execution mechanism can be launched using the
app-core.cuba:type=PersistenceManager JMX bean by calling its
updateDatabase() method with the
update parameter. Obviously, it is only possible to update already existing DB as it is impossible to log in to the system to run a method of the JMX bean with an empty DB. Please note, that an unrecoverable error will occur, if part of the data model no longer corresponding to the outdated DB schema is initialized during Middleware startup or user login. That is why the automatic update of the DB on the server startup before initializing the data model is only universal.
app-core.cuba:type=PersistenceManager bean has one more method related to the DB update mechanism:
findUpdateDatabaseScripts(). It returns a list of new update scripts available in the directory and not registered in the DB (not yet executed).
Recommendations for usage of the server DB update mechanism can be found in Creating and Updating the Database in Production.