java 将集合（'select *'）映射到 MyBatis 中的字段
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Mapping collection ('select *') to field in MyBatis
提问by David Warsow
I am stacked. I would like to replace direct use of sql in favor of mybatis faramework. I would like to select list of accounts with filled properties map.
我堆积如山。我想用mybatis faramework代替直接使用 sql 。我想选择带有填充属性映射的帐户列表。
But lets start from the beginning, first Account class
但是让我们从头开始，第一个 Account 类
public class Account {
private int id;
...
private Map<String, String> properties;
...
//setters / getters
}
Mapper interface for Account is obvious and mapping file contains selects
帐户的映射器接口很明显，映射文件包含选择
<select id="getAccountById" resultMap="account">
select ... from account where id = #{id}
</select>
<select id="getAccountProperties" resultType=map>
select * from properties where id=#{id}
</select>
First selection returns Account object, second java.util.Map contains column name/ valuepair.
第一个选择返回 Account 对象，第二个 java.util.Map 包含列名/值对。
I would like that each account object contain map with properties, so I iterate over list of accounts and selects its properties by id
我希望每个帐户对象都包含带有属性的映射，因此我遍历帐户列表并按 id 选择其属性
for(Account account : accountList) {
int id = account.getId();
Map properites = mapper.getAccountProperties(id);
account.setProperties(properties);
}
And basically it works, but for 200 accounts it takes about 2 minutes, and it is not acceptable.
而且基本上是可以的，但是200个账号大概需要2分钟，是不行的。
I hope that using resultMapwith collectionwill speed it up. But the question is how
to do it. How should resultMap="account"looks like
我希望使用resultMapwithcollection会加快速度。但问题是如何去做。应该怎么resultMap="account"看
<resultMap id="account" type="Account">
<id property="id" column="id">
...
<collection property="properties" javaType="map" column="id" select="getAccountProperties" />
</resultMap>
In this case selected account object does not contain any properties. The big question is: How to associate properties with account object?
在这种情况下，选定的帐户对象不包含任何属性。最大的问题是：如何将属性与帐户对象相关联？
回答by Andrea Colleoni
If you use the following resultmap
如果您使用以下结果图
<resultMap id="account" type="Account">
<result property="id" column="id">
<result property="properties" column="id" select="getAccountProperties" />
</resultMap>
Then for each account MyBatis executes the getAccountProperties statement passing the value of the column id as a parameter, but you must allow to accept it in the select tag:
然后对于每个帐户 MyBatis 执行 getAccountProperties 语句，将列 id 的值作为参数传递，但您必须允许在 select 标签中接受它：
<select id="getAccountProperties" resultClass="java.util.Map" parameterClass="java.lang.Integer" >
select * from properties where id=#value#
</select>
