I just generated an entity by reverse engineering the following table: CREATE TABLE FIDPUBLIC.CODES ( DOMINIO VARCHAR2(30 BYTE) NOT NULL, CODICE VARCHAR2(30 BYTE) NOT NULL, VALORE VARCHAR2(50 BYTE) NOT NULL, DESCRIZIONE VARCHAR2(50 BYTE), DATE_FROM DATE NOT NULL, DATE_TO DATE ) ALTER TABLE FIDPUBLIC.CODES ADD ( CONSTRAINT PK_CODES PRIMARY KEY (DOMINIO, CODICE, DATE_FROM) Idea correctly generated an entity with an Idclass: @Entity @Table( schema = "FIDPUBLIC", name = "CODES" ) @IdClass( CodePK.class ) public class Code { private String dominio; @Id @Column( name = "DOMINIO", nullable = false, length = 30 ) public String getDominio() { return dominio; } ... but the idclass is empty: public class CodePK implements Serializable { } (it should at least include the definitions for the same columns marked as @Id in the entity class, and hashcode and equals methods.