Hibernate select after insertion - mysql

Question

I'm having an issue with inserting new rows into my MySQL database. I'm using Spring Boot with Spring Boot Data JPA.
Since MySQL doesn't support sequences, I decided to try and make my own sequence generator table. This is basically what I've done.
I created a sequences table that uses an auto increment field (used as my id's for my tables).
Created a function, sequences_nextvalue() which inserts into the sequences table and returns the new auto incremented id.
I then created triggers on each table that get triggered before insertion and replaces the id field with the result of calling sequences_nextvalue().
So this is working fine when inserting new rows. I'm getting unique ids across all tables. The issue I'm having is with my JPA entities.
#Entity
#Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractBaseClass {
#Id
private Integer id = -1;
...
}
#Entity
public class ConcreteClass1 extends AbstractBaseClass {
...
}
#Entity
public class ConcreteClass2 extends AbstractBaseClass {
...
}
I want to be able to query from the abstract base class so I've placed my #Id column in that class and used #Entity with InheritanceType.TABLE_PER_CLASS. I've also initialized the id to -1 since an id is required to call save() from my spring crud repository.
After calling the save() function of my Spring data CrudRepository, the -1 for id properly gets replaced by the MySQL trigger but the resulting entity returned by save() doesn't return with the new id but instead retains the -1. After looking at the SQL logs, a select statement is not being called after insertion to get the new id but instead the original entity is being returned.
Is it possible to force Hibnerate to re-select the entity after insertion to get the new id when you're not using #GeneratedValue?
Any help is greatly appreciated.

Answer 1

Just wanted to provide an update on this question. Here is my solution.
Instead of creating MySQL TRIGGER's to replace the id on INSERT, I created a Hibernate IdentifierGenerator which executes a CallableStatement to get and return a new id.
My abstract base class now looks like this.
#Entity
#Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractBaseClass {
#Id
#GenericGenerator(name="MyIdGenerator", strategy="com.sample.model.CustomIdGenerator" )
#GeneratedValue(generator="MyIdGenerator" )
private Integer id;
...
}
and my generator looks like this.
public class CustomIdGenerator implements IdentifierGenerator {
private Logger log = LoggerFactory.getLogger(CustomIdGenerator.class);
private static final String QUERY = "{? = call sequence_nextvalue()}";
#Override
public Serializable generate(SessionImplementor session, Object object) throws HibernateException {
Integer id = null;
try {
Connection connection = session.connection();
CallableStatement statement = connection.prepareCall(QUERY);
statement.registerOutParameter(1, java.sql.Types.INTEGER);
statement.execute();
id = statement.getInt(1);
} catch(SQLException e) {
log.error("Error getting id", e);
throw new HibernateException(e);
}
return id;
}
}
And just for reference
The sequences table.
CREATE TABLE sequences (
id INT AUTO_INCREMENT PRIMARY KEY,
thread_id INT NOT NULL,
created DATETIME DEFAULT CURRENT_TIMESTAMP
) ^;
The sequence_nextvalue function
CREATE FUNCTION sequence_nextvalue()
RETURNS INTEGER
NOT DETERMINISTIC
MODIFIES SQL DATA
BEGIN
DECLARE nextvalue INTEGER;
INSERT INTO sequences (thread_id) VALUE (CONNECTION_ID());
SELECT id FROM sequence_values ORDER BY created DESC LIMIT 1 INTO nextvalue;
RETURN nextvalue;
END ^;