JPA查询::过滤外部联接结果

Question

I researched quite a bit before posting this, and I did implement a workaround that I don't like. I tried Hibernate's @Filter and @FilterDef annotations with little success, and I didn't like that option much anyway because it made my persistence layer dependent upon the provider framework. I am including one hibernate specific annotation in here, though, so my solution is not completely devoid of framework-specific code.

Basically, I have a Person class with family members that contains a collection of other Person's. I want to archive my data, and basically never physically delete anything, so all major objects in the app have a boolean 'deleted' value.

My basic problem was that I could not figure out a JPA query for filtering the familyMembers collection where I would only retrieve those family members that have not been deleted from the database.

@Entity
@Table(name="person")
class Person {
    private boolean deleted; 
    private List<Person> familyMembers;

    @ManyToMany(targetEntity=Person.class, cascade={ CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH }, fetch=FetchType.LAZY)
    @JoinTable(name = "hp_person_family", 
        joinColumns = { @JoinColumn(name = "person_id") }, inverseJoinColumns = { @JoinColumn(name = "family_person_id") }
    )
    @LazyCollection(LazyCollectionOption.FALSE)
    public List<Person> getFamilyMembers() {
        return familyMembers;
    }

    @Column(name = "deleted_flag")
    @Type(type = "yes_no")
    public boolean isDeleted() {
        return deleted;
    }

}

In my service implementation, I had this:

String personQuery = "SELECT DISTINCT(p) FROM Person p "
        + "LEFT JOIN FETCH p.familyMembers pf " 
        + "WHERE p.deleted = false " 
        +   "AND pf.deleted = false"; 
List<Person> people = em.createQuery(personQuery, Person.class) 
        .getResultList(); 

Which only returned those people that had a non-empty familyMembers collection, and only those that had not been deleted.

Next, I tried:

String personQuery = "SELECT DISTINCT(p) FROM Person p "
        + "LEFT JOIN FETCH p.familyMembers pf " 
        + "WHERE p.deleted = false"; 
List<Person> people = em.createQuery(personQuery, Person.class) 
        .getResultList(); 

This gets too many things ... all non-deleted people, but their familyMembers could have been deleted and they would still get retrieved.

Many syntax errors arose as I tried different "ON" statements and other asinine combinations that I desperately knew wouldn't work, but tried anyway.

Finally, I used the second version, and then used a Predicate object to filter the resulting familyMember collections. I get the results I want, but it means iterating through the collection (bring on the Lambdas in JDK1.8!!!) after retrieving it, just to filter out the baddies.

String personQuery = "SELECT DISTINCT(p) FROM Person p "
        + "LEFT JOIN FETCH p.familyMembers pf " 
        + "WHERE p.deleted = false"; 
List<Person> people = em.createQuery(personQuery, Person.class) 
        .getResultList(); 

filterPeopleResults(people); 




private void filterPeopleResults(List<Person> people) {
    if( people == null || people.isEmpty() ) return; 
    for(Person person : people) {
        removeDeletedFamilyMembers(person);
    }
}

private void removeDeletedFamilyMembers(Person person) {
    if( person.getFamilyMembers().isEmpty() == false ) {
        Predicate predicate = new Predicate() {
            @Override
            public boolean evaluate(Object obj) {
                if( ((Person)obj).isDeleted() ) return false; 
                return true; 
            }
        };
        CollectionUtils.filter(person.getFamilyMembers(), predicate);
    }
}

I've considered the possibility of pushing this logic up to the application level since I would only filter those Person objects I actually want to work with. Are there any other options I have using JPA, or some other clever JPQL syntax that would give me what I want?

Answer 1

Well there's the (hibernate specific) @Where annotation you can add to the collection definition.

Another option is to do a hard delete and use Hibernate Envers to maintain a full audit history. You can therefore always retrieve deleted entities from the audit tables and avoids the requirement to have all queries and collection mappings use 'where deleted = 0'

http://www.jboss.org/envers