How to use a custom function in a jpa query?

Question

I am new to Spring Jpa and Hibernate. I am trying to fetch data using a custom function from an Oracle db. I could define an entity along with its related service, implement

Answer 1

Unfortunately if you want to use the JPA 2.1 feature of the custom function call in your Select statement then you will need to perform some additional actions before you can use it.

When you use it in your where statement then it works without any additional actions, but as i wanted to use it for one of my projects inside the select just as you did then you would need to:

1) Extend the hibernate dialect and register your function(s):

package com.mypkg.dialect;

import org.hibernate.dialect.Oracle10gDialect;
import org.hibernate.dialect.function.StandardSQLFunction;
import org.hibernate.type.StringType;

public class CustomOracle10gDialect extends Oracle10gDialect {

    public CustomOracle10gDialect() {
        super();
        registerFunction("my_function"
           , new StandardSQLFunction("my_function", new StringType()));
    }
}

2) Edit your hibernate.dialect property of your session factory to point to that custom implementation:

Update

If the function needs to be called from a certain schema then this would be suggested:

registerFunction("my_function"
           , new StandardSQLFunction("schema.my_function", new StringType()));

Further reading -> native function calls