@Entity
@Table(name = "message")
public class Message extends AbstractEntity {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long messageId;

    @NotNull
    @MaxLength(400)
    private String message;

    @NotNull
    private OffsetDateTime dateSent;

}

<persistence version="2.1"
    xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="appdbPU" transaction-type="RESOURCE_LOCAL">
        <class>com.appslandia.app.entities.MessageGroup</class>

        <class>com.appslandia.app.entities.Message</class>
        <properties>
            <property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/appdb" />
            <property name="javax.persistence.jdbc.user" value="dbuser" />
            <property name="javax.persistence.jdbc.password" value="dbuser" />
            <property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" />

            <property name="hibernate.hbm2ddl.auto" value="create" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
            <property name="hibernate.show_sql" value="true" />
        </properties>
    </persistence-unit>
</persistence>

Hibernate: create table Message (messageId  bigserial not null, message varchar(255) not null,
dateSent bytea not null, primary key (messageId))