[1] Database script

create type GENDER_ENUM as enum ('male', 'female', 'unknown');
create sequence my_seq INCREMENT 1 MINVALUE 1 MAXVALUE 2147483647 START 1;
create table my_table (
  id            integer NOT NULL DEFAULT nextval('my_seq'),
  gender_type   GENDER_ENUM NOT NULL,

  CONSTRAINT my_table_pkey PRIMARY KEY(id)
);


insert into my_table (gender) values ('male');
insert into my_table (gender) values ('female');
insert into my_table (gender) values ('unknown');

[2] Persistence.xml file

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
    version="2.0" >

    <persistence-unit name="MyPersistenceUnit" transaction-type="RESOURCE_LOCAL">
        <description>Persistence unit</description>
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
            <property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/mydb" />
            <property name="javax.persistence.jdbc.user" value="user" />
            <property name="javax.persistence.jdbc.password" value="password" />

            <property name="hibernate.hbm2ddl.auto" value="validate"/>
            <property name="hibernate.show_sql" value="false" />
            <property name="hibernate.format_sql" value="false" />
            <property name="prefer_sequence_per_entity" value="true" />
        </properties>
    </persistence-unit>
</persistence>

[3] Entity code

package com.mypackage;

import java.sql.Timestamp;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Transient;

@Entity(name="my_table")
public class MyTable {

   @SequenceGenerator(name="generatorMySeq", sequenceName="my_seq", allocationSize=1)
   @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "generatorMySeq")
    @Id
    @Column(name = "id")
    private long id;

   @Enumerated(EnumType.STRING)
   @Column(name="gender_type", columnDefinition="GENDER_ENUM")
   private GenderEnum gender;
   
   // getters and setters
}

[4] My Java enumerated type

public enum GenderEnum {
   male, female, unknown;
}

[5] JUnit test

public class Test_MyTable {

    @Test
    public void test_1() {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("MyPersistenceUnit");
        EntityManager em = emf.createEntityManager();

      MyTable myTable = new MyTable();
      myTable.setGender(GenderEnum.male);

      em.getTransaction().begin();
      em.persist(ac);
      em.getTransaction().commit();

        em.close();
        emf.close();
    }
}

[6] Exception

The exception is:

Caused by: org.postgresql.util.PSQLException: ERROR: column “gender_type” is of type GENDER_ENUM but expression is of type character varying
Hint: You will need to rewrite or cast the expression.