1

我有经典设置

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

public class Child {
    Integer id;
    ...
}

我正在尝试使用 iBatis（版本 2.30 ......不要问）将其映射到通常的表设置上。

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

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

我的映射文件看起来像这样

<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>

一开始做通常sqlMap.queryForObject("loadParent", new Integer(42))的做法会导致 setter 内部出现 NullPointerException ，setChildren这显然是用 null 参数调用的（我的错）。修复 setter 一切正常，但是日志显示setChildren在运行单个 SQL 语句之前只调用了一次，仍然带有一个空参数，所以我想知道这里发生了什么。有人有任何线索吗？

4

2 回答 2

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。您的示例看起来不完整，因此我无法准确判断。

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进行比较，也许你会找出问题所在。

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');

豆子：

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>

如果你然后运行sqlMap.queryForObject("loadParent", new Integer(1))，或者sqlMap.queryForObject("loadParent", new Integer(2))你应该分别获得一个有两个孩子的父对象和一个有四个孩子的父对象。

于 2010-03-26T08:09:58.417 回答
0

我相信关键是在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>
于 2014-05-28T21:44:20.993 回答