热切/懒惰加载的成员总是空的,带有JPA一对多关系

我有两个实体,一个用户和一个角色,从用户到角色有一对多的关系。这是桌子的样子:

mysql> select * from User;
+----+-------+----------+
| id | name  | password |
+----+-------+----------+
|  1 | admin | admin    |
+----+-------+----------+
1 row in set (0.00 sec)

mysql> select * from Role;
+----+----------------------+---------------+----------------+
| id | description          | name          | summary        |
+----+----------------------+---------------+----------------+
|  1 | administrator's role | administrator | Administration |
|  2 | editor's role        | editor        | Editing        |
+----+----------------------+---------------+----------------+
2 rows in set (0.00 sec)

下面是创建的联接表:

mysql> select * from User_Role;
+---------+----------+
| User_id | roles_id |
+---------+----------+
|       1 |        1 |
|       1 |        2 |
+---------+----------+
2 rows in set (0.00 sec)

下面是 orm.xml 定义了表和关系:

<entity class="User" name="User">
    <table name="User" />
    <attributes>
        <id name="id">
            <generated-value strategy="AUTO" />
        </id>
        <basic name="name">
            <column name="name" length="100" unique="true" nullable="false"/>
        </basic>
        <basic name="password">
            <column length="255" nullable="false" />
        </basic>
        <one-to-many
            name="roles"
            fetch="EAGER"
            target-entity="Role"
            />
    </attributes>
</entity>

<entity class="Role" name="Role">
    <table name="Role" />
    <attributes>
        <id name="id">
            <generated-value strategy="AUTO"/>
        </id>
        <basic name="name">
            <column name="name" length="40" unique="true" nullable="false"/>
        </basic>
        <basic name="summary">
            <column name="summary" length="100" nullable="false"/>
        </basic>
        <basic name="description">
            <column name="description" length="255"/>
        </basic>
    </attributes>
</entity>

然而,尽管如此,当我检索管理用户时,我得到了一个空的集合。我使用Hibernate作为JPA提供程序,它显示以下调试SQL:

select
    user0_.id as id8_,
    user0_.name as name8_,
    user0_.password as password8_ 
from
    User user0_ 
where
    user0_.name=? limit ?

当一对多映射被延迟加载时,这是唯一进行的查询。这将正确检索一个管理员用户。我将关系更改为“使用预加载”,然后除上述内容外,还进行了以下查询:

select
    roles0_.User_id as User1_1_,
    roles0_.roles_id as roles2_1_,
    role1_.id as id9_0_,
    role1_.description as descript2_9_0_,
    role1_.name as name9_0_,
    role1_.summary as summary9_0_ 
from
    User_Role roles0_ 
left outer join
    Role role1_ 
        on roles0_.roles_id=role1_.id 
where
    roles0_.User_id=?

结果如下:

+----------+-----------+--------+----------------------+---------------+----------------+
| User1_1_ | roles2_1_ | id9_0_ | descript2_9_0_       | name9_0_      | summary9_0_    |
+----------+-----------+--------+----------------------+---------------+----------------+
|        1 |         1 |      1 | administrator's role | administrator | Administration |
|        1 |         2 |      2 | editor's role        | editor        | Editing        |
+----------+-----------+--------+----------------------+---------------+----------------+
2 rows in set (0.00 sec)

Hibernate显然知道角色 getRoles() 仍然返回空集合。Hibernate还充分认识到了将数据放在首位的关系。

哪些问题会导致这些症状?