使用HQL /用户执行哪种连接类型执行搜索？

Question

我有以下模型；

• 我有用户和规则
• 可以将一个用户添加到0、1个或多个规则
• 一个规则可以包含0、1个或多个用户

这是UserEntity类：

    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;
    }

    ...
}

和RuleEntity类：

    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;
      }

      ...
  }

我正在尝试实现一种搜索，以便用户可以使用以下方法进行搜索：

• 只有一个用户名
• 只有一个规则名
• 用户名和规则名

因此，我正在执行2个HQL查询，一个返回匹配的用户，另一个返回匹配的规则，例如

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);
}

当用户是至少一个规则的成员时，用于查找与用户名（和/或规则名称）匹配的用户的第一个HQL查询可以正常工作，但是当没有将用户添加到任何规则中时，它不会返回任何结果。

将“内部联接”更改为“左联接”无济于事。 问题出在'rules.ruleName like：maybePartialRuleName like'条件下，如果我删除了此查询就可以了，但是如果规则表的连接成功（例如，用户确实有规则），则需要在查询中使用它，因此，我需要按规则名称和用户名进行过滤。

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

尝试左加入

当用户离开时，从UserEntity中选择不同的用户加入用户users.rules作为规则，其中users.username如：maybePartialUsername和rules.ruleName如：maybePartialRuleName。

它将为您提供int左侧的所有功能（在本例中为userEntity）。

Answer 2

这对我有用（感谢@sergiu）：

以下方法创建查询的选择部分：

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);
  }

然后调用一个方法（未显示），该方法调用以下内容以构建查询的where部分：

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);
  }

还有一个由上述方法调用的辅助方法：

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