8.4. MySQL Database Specifics

The MySQL JDBC driver is not distributed with CUBA Studio due to the license restrictions, so you should do the following:

  • Download the driver archive from https://dev.mysql.com/downloads/connector/j

  • Extract JAR file and rename it to mysql-connector-java.jar

  • Copy the JAR file to the ~/.haulmont/studio/lib/ directory and to the lib subdirectory of the installed Tomcat server

  • Stop Studio and Gradle daemon by executing gradle --stop in the command line, then start Studio again

MySQL does not support partial indexes, so the only way to implement a unique constraint for a soft deleted entity is to use the DELETE_TS column in the index. But there is another problem: MySQL allows multiple NULLs in a column with a unique constraint. Since the standard DELETE_TS column is nullable, it cannot be used in the unique index. We recommend the following workaround for creating unique constraints for soft deleted entities:

  1. Create a DELETE_TS_NN column in the database table. This column is not null and is initialized by a default value:

    create table DEMO_CUSTOMER (
    ...
    DELETE_TS_NN datetime(3) not null default '1000-01-01 00:00:00.000',
    ...
)

  2. Create a trigger that will change DELETE_TS_NN value when DELETE_TS value is changed:

    create trigger DEMO_CUSTOMER_DELETE_TS_NN_TRIGGER before update on DEMO_CUSTOMER
for each row
    if not(NEW.DELETE_TS <=> OLD.DELETE_TS) then
        set NEW.DELETE_TS_NN = if (NEW.DELETE_TS is null, '1000-01-01 00:00:00.000', NEW.DELETE_TS);
    end if

  3. Create a unique index including unique columns and DELETE_TS_NN:

    create unique index IDX_DEMO_CUSTOMER_UNIQ_NAME on DEMO_CUSTOMER (NAME, DELETE_TS_NN)