Question

我有经典的设置

public class Parent {
    Integer id;
    ...
    // No generics
    Collection someCollectionAttribute;
    ...
    public void setChildren(Collection c) {
        ...
    }
}

public class Child {
    Integer id;
    ...
}

我试图使用iBatis（版本2.30 ......不要问）在通常的表格设置上映射它。

create table parents (
    ID integer primary key
    ...
)

create table children (
    ID integer primary key
    PARENT_ID integer references parents(id)
    ...
)

我的映射文件如下所示

<resultMap id="ParentResult" groupBy="id">
    <result property="id" column="ID" />
    ...
    <result property="children" resultMap="ChildResult" />
</resultMap>

<resultMap id="ChildResult">
    <result property="id" column="ID" />
    <result property="parentId" column="PARENT_ID" />
    ...
</result>

<sql id="loadParent" resultMap="ParentResult">
    select P.ID as p1, ..., C.ID as c1, C.PARENT_ID as c2 ...
    from   parents P
    join   children C on (P.ID = C.PARENT_ID)
    where  P.ID = #id#
    order by P.ID
</sql>

首先执行通常的sqlMap.queryForObject("loadParent", new Integer(42))会在setChildren setter中导致NullPointerException，显然是使用null参数调用的（我的错误）。修复setter一切正常，但日志显示setChildren在调用单个SQL语句之前只调用一次，仍然使用null参数，所以我想知道这里发生了什么。有人有任何线索吗？

Answer 1

我认为问题在于结果集中的列名（您指定的别名）与iBatis的结果映射中的映射不匹配。你的例子看起来不完整，所以我说不清楚。

无论如何，以下是与您的设置匹配的完整工作示例（使用iBatis 2.3.0.677测试）。如果你将它与你所拥有的相比较，那么你将找出问题所在。

数据库表：

create table parents (
    ID integer primary key,
    BLA VARCHAR(100)
);

insert into parents(id, bla) values
(1, 'text1'),
(2, 'text2');

create table children (
    ID integer primary key,
    PARENT_ID integer references parents(id),
    BLA_CHILD VARCHAR(100)
);

insert into children(id, parent_id, bla_child) values
(10, 1, 'child for 1 1'),
(11, 1, 'child for 1 2'),

(12, 2, 'child for 2 1'),
(13, 2, 'child for 2 2'),
(14, 2, 'child for 2 3'),
(15, 2, 'child for 2 4');

豆类：

package model.pack;
import java.util.Collection;
public class Parent {
    private Integer id;
    private String bla;
    private Collection children;

    public Collection getChildren() {
        return children;
    }
    public void setChildren(Collection children) {
        this.children = children;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getBla() {
        return bla;
    }
    public void setBla(String bla) {
        this.bla = bla;
    }
}

package model.pack;
public class Child {
    private Integer id;
    private Integer parentId;
    private String bla;

    public Integer getParentId() {
        return parentId;
    }
    public void setParentId(Integer parentId) {
        this.parentId = parentId;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getBla() {
        return bla;
    }
    public void setBla(String bla) {
        this.bla = bla;
    }
}

Sql映射：

<sqlMap>
    <resultMap id="childResult" class="model.pack.Child">
        <result property="id" column="childId" />
        <result property="parentId" column="childParentId" />
        <result property="bla" column="childBla" />
    </resultMap>

    <resultMap id="parentResult" class="model.pack.Parent" groupBy="id">
        <result property="id" column="parentId" />
        <result property="bla" column="parentBla" />
        <result property="children" resultMap="childResult" />
    </resultMap>

    <select id="loadParent" parameterClass="int" resultMap="parentResult">
        select p.id as parentId, p.bla as parentBla, c.id as childId, 
        c.bla_child as childBla, c.parent_id as childParentId
        from parents p left outer join children c
        on c.parent_id = p.id
        where p.id = #id#
        order by p.id
    </select>
</sqlMap>

如果您随后运行sqlMap.queryForObject("loadParent", new Integer(1))或sqlMap.queryForObject("loadParent", new Integer(2))，您应该获得一个包含两个孩子的父对象和一个有四个孩子的父母。

Answer 2

我认为关键是在resultMap中，应该使用而不是<result>.

<resultMap id="ParentResult" groupBy="id">
    <result property="id" column="ID" />
    ...
    <collection property="children" javaType="ArrayList" ofType="Child" resultMap="ChildResult" />
</resultMap>

<resultMap id="ChildResult">
    <result property="id" column="ID" />
    <association property="parentId" foreignColumn="PARENT_ID" resultMap="ParentResult" />
    ...
</result>

使用iBatis映射父子关系

2 个答案: