Perform search using HQL/which join type to user?

Question

I have the following model;

• I have users and rules
• a user can be added to 0, 1 or more rules
• a rule can contain 0, 1 or more users

Here is the UserEntity class:

    class UserEntity {

    private String username;

    private List<RuleEntity> rules;

    @Column(name = "username", nullable = false, unique = true)
    public String getUsername() {
        return username;
    }

    @ManyToMany(mappedBy="users" , fetch = FetchType.LAZY)
    public List<RuleEntity> getRules() {
        return rules;
    }

    ...
}

And the RuleEntity class:

    class RuleEntity {
        private String name;

        private List<UserEntity> users;

        @Column(name = "name", nullable = false)
        public String getRuleName() {
             return ruleName;
        }

        @ManyToMany (fetch = FetchType.LAZY)
        @JoinTable(name= "RULE_USER" ,joinColumns=@JoinColumn
        (name=RuleEntity.RULE_ID, referencedColumnName="ID", insertable = true, updatable = false, nullable = false),
      inverseJoinColumns=@JoinColumn
      (name=UserEntity.USER_ID, referencedColumnName="ID", insertable = true, updatable = false, nullable = false), 
      uniqueConstraints = @UniqueConstraint(columnNames = {RuleEntity.RULE_ID, UserEntity.USER_ID}))
      public List<UserEntity> getUsers() {
         return users;
      }

      ...
  }

I am trying to implement a search whereby a user can search using:

• only a username
• only a rulename
• a username and a rulename

So I am performing 2 HQL queries, one to return the matching users and one to return the matching rules e.g.

public SearchResults search(String maybePartialUsername, String maybePartialRuleName) {
    List<UserEntity> userEntities = hqlQuery("select distinct users from UserEntity as users inner join users.rules as rules where users.username like :maybePartialUsername and rules.ruleName like :maybePartialRuleName");

    List<RuleEntity> ruleEntities = hqlQuery("select distinct rules from RuleEntity as rules inner join rules.users as users where users.username like :maybePartialUsername and rules.ruleName like :maybePartialRuleName");

    return SearchResults(userEntities, ruleEntities);
}

The first HQL query for finding users matching a username (and/or rulename) works fine when a user is a member of at least one rule, but it returns no results when a user has not been added to any rules.

Changing the 'inner join' to a 'left join' does not help. The problem lies in the 'rules.ruleName like :maybePartialRuleName' condition, if I remove this the query works, but I need this in the query in the cases where the join with the rules tables succeeds (i.e. a user DOES have rules), and thus I then need to filter by rule name as well as username.

select distinct users from UserEntity as users inner join users.rules as rules where users.username like :maybePartialUsername and rules.ruleName like :maybePartialRuleName

Answer 1

This is what worked for me (thanks @sergiu):

The following method creates the select part of the query:

public List<UserEntity> search(final String maybePartialUsername, final String maybePartialRuleName)
      throws EntityException {
    final String selectUsersStatement = "select distinct users from UserEntity as users";
    final String joinUsersWithRulesClause = shouldFilterSearchBy(maybePartialRuleName) ? "inner join users.rules as rules" : null;


    return search(Joiner.on(" ").skipNulls().join(selectUsersStatement, joinUsersWithRulesClause),
        maybePartialUsername, maybePartialRuleName);
  }

Which then calls a method (not shown) which calls the following to build the where parts of the query:

private String buildSearchQueryFrom(final String selectStatement, final String maybePartialUsername,
      final String maybePartialRuleName) {
    final Collection<String> searchFilters = Lists.newArrayListWithCapacity(2);

    if (shouldFilterSearchBy(maybePartialUsername)) {
      searchFilters.add("users.username like :maybePartialUsername");
    }

    if (shouldFilterSearchBy(maybePartialRuleName)) {
      searchFilters.add("rules.ruleName like :maybePartialRuleName");
    }

    final String whereClauseParts = Joiner.on(" and ").skipNulls().join(searchFilters);
    return Joiner.on(" where ").skipNulls().join(selectStatement, whereClauseParts);
  }

And a helper method called by the method above:

protected boolean shouldFilterSearchBy(final String searchValue) {
        return !Strings.isNullOrEmpty(searchValue);
      }

Answer 2

Try left join

select distinct users from UserEntity as users left join users.rules as rules where users.username like :maybePartialUsername and rules.ruleName like :maybePartialRuleName.

It will give you all that's int left side (userEntity in this case).