javax.persistence.criteria.SetJoin Java Examples

@Test
public void getBooks() {
	log.info("... getBooks ...");

	EntityManager em = emf.createEntityManager();
	em.getTransaction().begin();

	CriteriaBuilder cb = em.getCriteriaBuilder();
	CriteriaQuery<Book> cq = cb.createQuery(Book.class);
	Root<Book> root = cq.from(Book.class);
	SetJoin<Book, Author> authors = root.join(Book_.authors);
	
	ParameterExpression<String> paramFirstName = cb.parameter(String.class);
	ParameterExpression<String> paramLastName = cb.parameter(String.class);
	cq.where(
		cb.and(
			cb.equal(authors.get(Author_.firstName), paramFirstName), 
			cb.equal(authors.get(Author_.lastName), paramLastName)));
	
	TypedQuery<Book> query = em.createQuery(cq);
	query.setParameter(paramFirstName, "Thorben");
	query.setParameter(paramLastName, "Janssen");
	List<Book> books = query.getResultList();
	Assert.assertEquals(1, books.size());
	
	for (Book b : books) {
		log.info(b);
	}
	
	em.getTransaction().commit();
	em.close();
}
 

private static Predicate getPredicate(final SetJoin<JpaDistributionSet, JpaDistributionSetTag> tags,
        final Collection<String> tagNames, final Boolean selectDSWithNoTag, final CriteriaBuilder cb) {
    tags.get(JpaDistributionSetTag_.name);
    final Path<String> exp = tags.get(JpaDistributionSetTag_.name);
    if (selectDSWithNoTag != null && selectDSWithNoTag) {
        if (!CollectionUtils.isEmpty(tagNames)) {
            return cb.or(exp.isNull(), exp.in(tagNames));
        } else {
            return exp.isNull();
        }
    } else {
        return exp.in(tagNames);
    }
}
 

public static Predicate<BuildRecord> withArtifactDistributedInMilestone(Integer productMilestoneId) {
    return (root, query, cb) -> {
        SetJoin<BuildRecord, Artifact> builtArtifacts = root.join(BuildRecord_.builtArtifacts);
        SetJoin<Artifact, ProductMilestone> productMilestones = builtArtifacts
                .join(Artifact_.distributedInProductMilestones);
        return cb.equal(productMilestones.get(ProductMilestone_.id), productMilestoneId);
    };
}
 

public static Predicate<BuildConfiguration> withBuildConfigurationSetId(Integer buildConfigurationSetId) {
    return (root, query, cb) -> {
        SetJoin<BuildConfiguration, BuildConfigurationSet> configurationBuildConfigurationSetSetJoin = root
                .join(BuildConfiguration_.buildConfigurationSets);
        return cb.equal(
                configurationBuildConfigurationSetSetJoin.get(BuildConfigurationSet_.id),
                buildConfigurationSetId);
    };
}
 

/**
 * This predicate returns all the ProductVersions linked to a specified BuildConfiguration
 */
public static Predicate<ProductVersion> withBuildConfigurationId(Integer buildConfigurationId) {
    return (root, query, cb) -> {
        SetJoin<ProductVersion, BuildConfiguration> buildConfigurationJoin = root
                .join(ProductVersion_.buildConfigurations);
        return cb.equal(buildConfigurationJoin.get(BuildConfiguration_.id), buildConfigurationId);
    };
}
 

public static Predicate<BuildRecord> withAttribute(String key, String value) {
    return (root, query, cb) -> {
        SetJoin<BuildRecord, BuildRecordAttribute> joinAttributer = root.join(BuildRecord_.attributes);
        return query
                .where(
                        cb.and(cb.equal(joinAttributer.get(BuildRecordAttribute_.key), key)),
                        cb.equal(joinAttributer.get(BuildRecordAttribute_.value), value))
                .getRestriction();
    };
}
 

public static Predicate<BuildConfigurationSet> withBuildConfigurationId(Integer buildConfigurationId) {
    return (root, query, cb) -> {
        SetJoin<BuildConfigurationSet, BuildConfiguration> buildConfigsJoin = root
                .join(BuildConfigurationSet_.buildConfigurations);
        return cb.equal(buildConfigsJoin.get(BuildConfiguration_.id), buildConfigurationId);
    };
}
 

/**
 * {@link Specification} for retrieving {@link Target}s by tag.
 *
 * @param tagId
 *            the ID of the distribution set which must be assigned
 * @return the {@link Target} {@link Specification}
 */
public static Specification<JpaTarget> hasTag(final Long tagId) {

    return (targetRoot, query, cb) -> {
        final SetJoin<JpaTarget, JpaTargetTag> tags = targetRoot.join(JpaTarget_.tags, JoinType.LEFT);
        return cb.equal(tags.get(JpaTargetTag_.id), tagId);
    };
}
 

private static Predicate getPredicate(final Root<JpaTarget> targetRoot, final CriteriaBuilder cb,
        final Boolean selectTargetWithNoTag, final String[] tagNames) {
    final SetJoin<JpaTarget, JpaTargetTag> tags = targetRoot.join(JpaTarget_.tags, JoinType.LEFT);
    final Path<String> exp = tags.get(JpaTargetTag_.name);
    if (selectTargetWithNoTag) {
        if (tagNames != null) {
            return cb.or(exp.isNull(), exp.in(tagNames));
        } else {
            return exp.isNull();
        }
    } else {
        return exp.in(tagNames);
    }
}
 

/**
 * {@link Specification} for retrieving {@link DistributionSet}s by tag.
 *
 * @param tagId
 *            the ID of the distribution set which must be assigned
 * @return the {@link DistributionSet} {@link Specification}
 */
public static Specification<JpaDistributionSet> hasTag(final Long tagId) {

    return (targetRoot, query, cb) -> {
        final SetJoin<JpaDistributionSet, JpaDistributionSetTag> tags = targetRoot.join(JpaDistributionSet_.tags,
                JoinType.LEFT);
        return cb.equal(tags.get(JpaDistributionSetTag_.id), tagId);
    };
}
 

/**
 * {@link Specification} for retrieving {@link DistributionSet}s by "has at
 * least one of the given tag names".
 * 
 * @param tagNames
 *            to be filtered on
 * @param selectDSWithNoTag
 *            flag to select distribution sets with no tag
 * @return the {@link DistributionSet} {@link Specification}
 */
public static Specification<JpaDistributionSet> hasTags(final Collection<String> tagNames,
        final Boolean selectDSWithNoTag) {
    return (targetRoot, query, cb) -> {
        final SetJoin<JpaDistributionSet, JpaDistributionSetTag> tags = targetRoot.join(JpaDistributionSet_.tags,
                JoinType.LEFT);
        final Predicate predicate = getPredicate(tags, tagNames, selectDSWithNoTag, cb);
        query.distinct(true);
        return predicate;
    };
}
 

/**
    * Helper function to return a specification for filtering on one-to-many or many-to-many reference.Where equality, less
than, greater than and less-than-or-equal-to and greater-than-or-equal-to and null/non-null conditions are
supported. Usage:
<pre><code>
    *   Specification&lt;Employee&gt; specByEmployeeId = buildReferringEntitySpecification(
    *          criteria.getEmployeId(),
    *          root -&gt; root.get(Project_.company).join(Company_.employees),
    *          entity -&gt; entity.get(Employee_.id));
    *   Specification&lt;Employee&gt; specByProjectName = buildReferringEntitySpecification(
    *          criteria.getProjectName(),
    *          root -&gt; root.get(Project_.project)
    *          entity -&gt; entity.get(Project_.name));
    * </code>
    * </pre>
    *
    * @param <X>              The type of the attribute which is filtered.
    * @param filter           the filter object which contains a value, which needs to match or a flag if emptiness is
    *                         checked.
    * @param functionToEntity the function, which joins he current entity to the entity set, on which the filtering is applied.
    * @param entityToColumn   the function, which of the static metamodel of the referred entity, where the equality should be
    *                         checked.
    * @param <OTHER>          The type of the referenced entity.
    * @param <MISC>           The type of the entity which is the last before the OTHER in the chain.
    * @return a Specification
    */
   protected <OTHER, MISC, X extends Comparable<? super X>> Specification<ENTITY> buildReferringEntitySpecification(final RangeFilter<X> filter,
                                                                                                                    Function<Root<ENTITY>, SetJoin<MISC, OTHER>> functionToEntity,
                                                                                                                    Function<SetJoin<MISC, OTHER>, Expression<X>> entityToColumn) {

       Function<Root<ENTITY>, Expression<X>> fused = functionToEntity.andThen(entityToColumn);
       if (filter.getEquals() != null) {
           return equalsSpecification(fused, filter.getEquals());
       } else if (filter.getIn() != null) {
           return valueIn(fused, filter.getIn());
       }
       Specification<ENTITY> result = Specification.where(null);
       if (filter.getSpecified() != null) {
           // Interestingly, 'functionToEntity' doesn't work, we need the longer lambda formula
           result = result.and(byFieldSpecified(root -> functionToEntity.apply(root), filter.getSpecified()));
       }
       if (filter.getNotEquals() != null) {
           result = result.and(notEqualsSpecification(fused, filter.getNotEquals()));
       }
       if (filter.getNotIn() != null) {
           result = result.and(valueNotIn(fused, filter.getNotIn()));
       }
       if (filter.getGreaterThan() != null) {
           result = result.and(greaterThan(fused, filter.getGreaterThan()));
       }
       if (filter.getGreaterThanOrEqual() != null) {
           result = result.and(greaterThanOrEqualTo(fused, filter.getGreaterThanOrEqual()));
       }
       if (filter.getLessThan() != null) {
           result = result.and(lessThan(fused, filter.getLessThan()));
       }
       if (filter.getLessThanOrEqual() != null) {
           result = result.and(lessThanOrEqualTo(fused, filter.getLessThanOrEqual()));
       }
       return result;
   }
 

private List<Integer> getDependentMilestoneIds(CriteriaBuilder cb, String id) {
    CriteriaQuery<Integer> buildQuery = cb.createQuery(Integer.class);

    Root<Artifact> artifact = buildQuery.from(Artifact.class);
    SetJoin<Artifact, BuildRecord> build = artifact.join(Artifact_.dependantBuildRecords);
    buildQuery.where(cb.equal(artifact.get(Artifact_.id), Integer.valueOf(id)));
    buildQuery.select(build.get(BuildRecord_.productMilestone).get(ProductMilestone_.id));
    buildQuery.distinct(true);

    List<Integer> resultList = em.createQuery(buildQuery).getResultList();
    return resultList;
}
 

@Override
@SuppressWarnings({"unchecked"})
public <X, Y> SetJoin<X, Y> joinSet(String attributeName, JoinType jt) {
	final Attribute<X, ?> attribute = (Attribute<X, ?>) locateAttribute( attributeName );
	if ( !attribute.isCollection() ) {
		throw new IllegalArgumentException( "Requested attribute was not a set" );
	}

	final PluralAttribute pluralAttribute = (PluralAttribute) attribute;
	if ( !PluralAttribute.CollectionType.SET.equals( pluralAttribute.getCollectionType() ) ) {
		throw new IllegalArgumentException( "Requested attribute was not a set" );
	}

	return (SetJoin<X, Y>) join( (SetAttribute) attribute, jt );
}
 

@Override
public <X, Y> SetJoin<X, Y> correlate(SetJoin<X, Y> source) {
	final SetJoinImplementor<X,Y> correlation = ( (SetJoinImplementor<X,Y>) source ).correlateTo( this );
	queryStructure.addCorrelationRoot( correlation );
	return correlation;
}
 

@BeforeEach
@SuppressWarnings("unchecked")
void setup() {
    this.root = (Root<ClusterEntity>) Mockito.mock(Root.class);
    this.cq = Mockito.mock(CriteriaQuery.class);
    this.cb = Mockito.mock(CriteriaBuilder.class);

    final Path<Long> idPath = (Path<Long>) Mockito.mock(Path.class);
    Mockito.when(this.root.get(ClusterEntity_.id)).thenReturn(idPath);

    final Path<String> clusterNamePath = (Path<String>) Mockito.mock(Path.class);
    final Predicate likeNamePredicate = Mockito.mock(Predicate.class);
    final Predicate equalNamePredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ClusterEntity_.name)).thenReturn(clusterNamePath);
    Mockito.when(this.cb.like(clusterNamePath, NAME)).thenReturn(likeNamePredicate);
    Mockito.when(this.cb.equal(clusterNamePath, NAME)).thenReturn(equalNamePredicate);

    final Path<Instant> minUpdatePath = (Path<Instant>) Mockito.mock(Path.class);
    final Predicate greaterThanOrEqualToPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ClusterEntity_.updated)).thenReturn(minUpdatePath);
    Mockito.when(this.cb.greaterThanOrEqualTo(minUpdatePath, MIN_UPDATE_TIME))
        .thenReturn(greaterThanOrEqualToPredicate);

    final Path<Instant> maxUpdatePath = (Path<Instant>) Mockito.mock(Path.class);
    final Predicate lessThanPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ClusterEntity_.updated)).thenReturn(maxUpdatePath);
    Mockito.when(this.cb.lessThan(maxUpdatePath, MAX_UPDATE_TIME)).thenReturn(lessThanPredicate);

    final Path<String> statusPath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalStatusPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ClusterEntity_.status)).thenReturn(statusPath);
    Mockito
        .when(this.cb.equal(Mockito.eq(statusPath), Mockito.anyString()))
        .thenReturn(equalStatusPredicate);

    this.tagEntityJoin = (SetJoin<ClusterEntity, TagEntity>) Mockito.mock(SetJoin.class);
    Mockito.when(this.root.join(ClusterEntity_.tags)).thenReturn(this.tagEntityJoin);
    final Predicate tagInPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.tagEntityJoin.in(TAGS)).thenReturn(tagInPredicate);

    final Expression<Long> idCountExpression = (Expression<Long>) Mockito.mock(Expression.class);
    Mockito.when(this.cb.count(Mockito.any())).thenReturn(idCountExpression);
    final Predicate havingPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.cb.equal(idCountExpression, TAGS.size())).thenReturn(havingPredicate);
}
 

public static Predicate<BuildRecord> withArtifactDependency(Integer artifactId) {
    return (root, query, cb) -> {
        SetJoin<BuildRecord, Artifact> dependencies = root.join(BuildRecord_.dependencies);
        return cb.equal(dependencies.get(Artifact_.id), artifactId);
    };
}
 

@BeforeEach
@SuppressWarnings("unchecked")
void setup() {
    this.root = (Root<CommandEntity>) Mockito.mock(Root.class);
    this.cq = Mockito.mock(CriteriaQuery.class);
    this.cb = Mockito.mock(CriteriaBuilder.class);

    final Path<Long> idPath = (Path<Long>) Mockito.mock(Path.class);
    Mockito.when(this.root.get(CommandEntity_.id)).thenReturn(idPath);

    final Path<String> commandNamePath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalNamePredicate = Mockito.mock(Predicate.class);
    final Predicate likeNamePredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(CommandEntity_.name)).thenReturn(commandNamePath);
    Mockito.when(this.cb.equal(commandNamePath, NAME)).thenReturn(equalNamePredicate);
    Mockito.when(this.cb.like(commandNamePath, NAME)).thenReturn(likeNamePredicate);

    final Path<String> userNamePath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalUserNamePredicate = Mockito.mock(Predicate.class);
    final Predicate likeUserNamePredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(CommandEntity_.user)).thenReturn(userNamePath);
    Mockito.when(this.cb.equal(userNamePath, USER_NAME)).thenReturn(equalUserNamePredicate);
    Mockito.when(this.cb.like(userNamePath, USER_NAME)).thenReturn(likeUserNamePredicate);

    final Path<String> statusPath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalStatusPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(CommandEntity_.status)).thenReturn(statusPath);
    Mockito
        .when(this.cb.equal(Mockito.eq(statusPath), Mockito.anyString()))
        .thenReturn(equalStatusPredicate);

    this.tagEntityJoin = (SetJoin<CommandEntity, TagEntity>) Mockito.mock(SetJoin.class);
    Mockito.when(this.root.join(CommandEntity_.tags)).thenReturn(this.tagEntityJoin);
    final Predicate tagInPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.tagEntityJoin.in(TAGS)).thenReturn(tagInPredicate);

    final Expression<Long> idCountExpression = (Expression<Long>) Mockito.mock(Expression.class);
    Mockito.when(this.cb.count(Mockito.any())).thenReturn(idCountExpression);
    final Predicate havingPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.cb.equal(idCountExpression, TAGS.size())).thenReturn(havingPredicate);
}
 

@BeforeEach
@SuppressWarnings("unchecked")
void setup() {
    this.root = (Root<ApplicationEntity>) Mockito.mock(Root.class);
    this.cq = Mockito.mock(CriteriaQuery.class);
    this.cb = Mockito.mock(CriteriaBuilder.class);

    final Path<Long> idPath = (Path<Long>) Mockito.mock(Path.class);
    Mockito.when(this.root.get(ApplicationEntity_.id)).thenReturn(idPath);

    final Path<String> namePath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalNamePredicate = Mockito.mock(Predicate.class);
    final Predicate likeNamePredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ApplicationEntity_.name)).thenReturn(namePath);
    Mockito.when(this.cb.equal(namePath, NAME)).thenReturn(equalNamePredicate);
    Mockito.when(this.cb.like(namePath, NAME)).thenReturn(likeNamePredicate);

    final Path<String> userNamePath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalUserNamePredicate = Mockito.mock(Predicate.class);
    final Predicate likeUserNamePredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ApplicationEntity_.user)).thenReturn(userNamePath);
    Mockito.when(this.cb.equal(userNamePath, USER_NAME)).thenReturn(equalUserNamePredicate);
    Mockito.when(this.cb.like(userNamePath, USER_NAME)).thenReturn(likeUserNamePredicate);

    final Path<String> statusPath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalStatusPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ApplicationEntity_.status)).thenReturn(statusPath);
    Mockito
        .when(this.cb.equal(Mockito.eq(statusPath), Mockito.anyString()))
        .thenReturn(equalStatusPredicate);

    this.tagEntityJoin = (SetJoin<ApplicationEntity, TagEntity>) Mockito.mock(SetJoin.class);
    Mockito.when(this.root.join(ApplicationEntity_.tags)).thenReturn(this.tagEntityJoin);
    final Predicate tagInPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.tagEntityJoin.in(TAGS)).thenReturn(tagInPredicate);

    final Expression<Long> idCountExpression = (Expression<Long>) Mockito.mock(Expression.class);
    Mockito.when(this.cb.count(Mockito.any())).thenReturn(idCountExpression);
    final Predicate havingPredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.cb.equal(idCountExpression, TAGS.size())).thenReturn(havingPredicate);

    final Path<String> typePath = (Path<String>) Mockito.mock(Path.class);
    final Predicate equalTypePredicate = Mockito.mock(Predicate.class);
    final Predicate likeTypePredicate = Mockito.mock(Predicate.class);
    Mockito.when(this.root.get(ApplicationEntity_.type)).thenReturn(typePath);
    Mockito.when(this.cb.equal(typePath, TYPE)).thenReturn(equalTypePredicate);
    Mockito.when(this.cb.like(typePath, TYPE)).thenReturn(likeTypePredicate);
}
 

public static Predicate<BuildRecord> withArtifactProduced(Integer artifactId) {
    return (root, query, cb) -> {
        SetJoin<BuildRecord, Artifact> builtArtifacts = root.join(BuildRecord_.builtArtifacts);
        return cb.equal(builtArtifacts.get(Artifact_.id), artifactId);
    };
}
 

public static Predicate<BuildConfiguration> withDependantConfiguration(Integer parentBuildConfigurationId) {
    return (root, query, cb) -> {
        SetJoin<BuildConfiguration, BuildConfiguration> dependantBuildConfigurationsJoin = root
                .join(BuildConfiguration_.dependants);
        return cb.equal(dependantBuildConfigurationsJoin.get(BuildConfiguration_.id), parentBuildConfigurationId);
    };
}
 

@Override
public <X, Y> SetJoin<X, Y> joinSet(String attributeName) {
	return joinSet( attributeName, DEFAULT_JOIN_TYPE );
}
 

@Override
public <Y> SetJoin<X, Y> join(SetAttribute<? super X, Y> set) {
	return join( set, DEFAULT_JOIN_TYPE );
}
 

@Override
@SuppressWarnings("unchecked")
public <X, T, E extends T> SetJoin<X, E> treat(SetJoin<X, T> join, Class<E> type) {
	return treat( join, type, (j, t) -> ((SetJoinImplementor) j).treatAs( t ) );
}
 

/**
 * Specification which joins all necessary tables to retrieve the dependency
 * between a target and a local file assignment through the assigned action
 * of the target. All actions are included, not only active actions.
 * 
 * @param targetId
 *            the target to verify if the given artifact is currently
 *            assigned or had been assigned
 * @param sha1Hash
 *            of the local artifact to check wherever the target had ever
 *            been assigned
 * @return a specification to use with spring JPA
 */
public static Specification<JpaAction> hasTargetAssignedArtifact(final Long targetId, final String sha1Hash) {
    return (actionRoot, query, criteriaBuilder) -> {
        final Join<JpaAction, JpaDistributionSet> dsJoin = actionRoot.join(JpaAction_.distributionSet);
        final SetJoin<JpaDistributionSet, JpaSoftwareModule> modulesJoin = dsJoin.join(JpaDistributionSet_.modules);
        final ListJoin<JpaSoftwareModule, JpaArtifact> artifactsJoin = modulesJoin
                .join(JpaSoftwareModule_.artifacts);
        return criteriaBuilder.and(criteriaBuilder.equal(artifactsJoin.get(JpaArtifact_.sha1Hash), sha1Hash),
                criteriaBuilder.equal(actionRoot.get(JpaAction_.target).get(JpaTarget_.id), targetId));
    };
}
 

/**
 * Specification which joins all necessary tables to retrieve the dependency
 * between a target and a local file assignment through the assigned action
 * of the target. All actions are included, not only active actions.
 * 
 * @param controllerId
 *            the target to verify if the given artifact is currently
 *            assigned or had been assigned
 * @param sha1Hash
 *            of the local artifact to check wherever the target had ever
 *            been assigned
 * @return a specification to use with spring JPA
 */
public static Specification<JpaAction> hasTargetAssignedArtifact(final String controllerId, final String sha1Hash) {
    return (actionRoot, query, criteriaBuilder) -> {
        final Join<JpaAction, JpaDistributionSet> dsJoin = actionRoot.join(JpaAction_.distributionSet);
        final SetJoin<JpaDistributionSet, JpaSoftwareModule> modulesJoin = dsJoin.join(JpaDistributionSet_.modules);
        final ListJoin<JpaSoftwareModule, JpaArtifact> artifactsJoin = modulesJoin
                .join(JpaSoftwareModule_.artifacts);
        return criteriaBuilder.and(criteriaBuilder.equal(artifactsJoin.get(JpaArtifact_.sha1Hash), sha1Hash),
                criteriaBuilder.equal(actionRoot.get(JpaAction_.target).get(JpaTarget_.controllerId),
                        controllerId));
    };
}
 

/**
 * Helper function to return a specification for filtering on one-to-many or many-to-many reference.Usage:<pre>
 *   Specification&lt;Employee&gt; specByEmployeeId = buildReferringEntitySpecification(
 *          criteria.getEmployeId(),
 *          root -&gt; root.get(Project_.company).join(Company_.employees),
 *          entity -&gt; entity.get(Employee_.id));
 *   Specification&lt;Employee&gt; specByProjectName = buildReferringEntitySpecification(
 *          criteria.getProjectName(),
 *          root -&gt; root.get(Project_.project)
 *          entity -&gt; entity.get(Project_.name));
 * </pre>
 *
 * @param filter           the filter object which contains a value, which needs to match or a flag if emptiness is
 *                         checked.
 * @param functionToEntity the function, which joins he current entity to the entity set, on which the filtering is applied.
 * @param entityToColumn   the function, which of the static metamodel of the referred entity, where the equality should be
 *                         checked.
 * @param <OTHER>          The type of the referenced entity.
 * @param <MISC>           The type of the entity which is the last before the OTHER in the chain.
 * @param <X>              The type of the attribute which is filtered.
 * @return a Specification
 */
protected <OTHER, MISC, X> Specification<ENTITY> buildReferringEntitySpecification(Filter<X> filter,
                                                                                   Function<Root<ENTITY>, SetJoin<MISC, OTHER>> functionToEntity,
                                                                                   Function<SetJoin<MISC, OTHER>, Expression<X>> entityToColumn) {
    if (filter.getEquals() != null) {
        return equalsSpecification(functionToEntity.andThen(entityToColumn), filter.getEquals());
    } else if (filter.getSpecified() != null) {
        // Interestingly, 'functionToEntity' doesn't work, we need the longer lambda formula
        return byFieldSpecified(root -> functionToEntity.apply(root), filter.getSpecified());
    }
    return null;
}