Java 使用HQL/对用户执行哪种连接类型的搜索？

我有以下模型

• 我有用户和规则
• 可以将用户添加到0、1或更多规则中
• 规则可以包含0、1或多个用户

以下是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;
    }

    ...
}

    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;
      }

      ...
  }

尝试左连接

从UserEntity中选择不同的用户作为左用户加入users.rules作为规则，其中users.username类似：MaybeApartialUserName和rules.ruleName类似：MaybeApartialRuleName

---

它将为您提供所有int左边的内容（本例中为userEntity）。

这对我来说很有用（谢谢@sergiu）：

以下方法创建查询的select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);
  }

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);
  }

---

谢谢，虽然左连接也不起作用，但它会像内部连接一样返回零结果，问题是，对于左/内部连接，sql“rules.ruleName”的这一部分（如：maybeapartialruleName）会导致结果返回零结果。是否有一条记录同时满足这两个条件？不，在这种情况下，用户没有规则。好的，因此，只有当条件不为null或空时，才需要传递这些条件。例如，如果maybePartialRuleName为null或为空，则查询将不包含“and rules.ruleName like:maybePartialRuleName”。这同样适用于其他条件。必须使用内部连接。谢谢@sergiu，我已经根据您的评论更新了我的答案。

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);
  }

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);
  }

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