get max value of column using jpa criteria query - jpa

Question

I want to get the maximum value of column relationId from table ElementRelationType
I have written code but its giving error
CriteriaBuilder cb1 = entityManager.getCriteriaBuilder();
CriteriaQuery<ElementRelationTypes> cq1 = cb1.createQuery(ElementRelationTypes.class);
Root<ElementRelationTypes> root = cq1.from(ElementRelationTypes.class);
cq1.select(cb1.max(root.get("relationId")));
select and max both giving error
how to get the integer max value
public class ElementRelationTypes {
private RelationId relationLangPK=new RelationId();
private Country country;
private Status status;
#EmbeddedId
public RelationId getRelationLangPK() {
return relationLangPK;
}
public void setRelationLangPK(RelationId relationLangPK) {
this.relationLangPK = relationLangPK;
}
#Transient
public Integer getRelationId() {
return getRelationLangPK().getRelationId();
}
public void setRelationId(Integer relationId) {
getRelationLangPK().setRelationId(relationId);
}
#Transient
public Language getLanguage() {
return getRelationLangPK().getLanguage();
}
public void setLanguageCode(Language language) {
getRelationLangPK().setLanguage(language);
}
and
public class RelationId implements Serializable {
private static final long serialVersionUID = 1L;
private Integer relationId;
private Language language;
#JoinColumn(name=PersistenseConstants.ELEMENT_RELATION_TYPE_COL_RELATION_ID)
public Integer getRelationId() {
return relationId;
}
public void setRelationId(Integer relationId) {
this.relationId = relationId;
}
#OneToOne
#JoinColumn(name=PersistenseConstants.LANGUAGE_ENTITY_COL_LANG_CODE)
public Language getLanguage() {
return language;
}
public void setLanguage(Language language) {
this.language = language;
}

Answer 1

You didn't post which errors do you receive, so I have to guess.
CriteriaBuilder.max accepts Expression<N> where N extends Number
At the same time Root.get by default returns Path<Object> which is inconvertible to Expression<Number>.
So to make your call to max work you need to specify generic parameter to root.get:
cq1.select(cb1.max(root.<Number>get("relationId")));
here you can replace Number with an actual type of relationId (Long, BigInteger etc.)
UPDATE: #perissf addressed another issue with your code. If you are going to select maximal value (which is numeric) you should declare your CriteriaQuery as a query to Number not ElementRelationTypes