Mybatis resultMap空值映射问题解决
Mybatis在使用resultMap来映射查询结果中的列,如果查询结果中包含空值的列(不是null),则Mybatis在映射的时候,不会映射这个字段,例如 查询 name,sex,age,数据库中的age字段没有值,Mybatis返回的map中只映射了 name和sex字段,而age字段则没有包含。
那么如何将age字段映射到map中呢。提供两种解决方法:
使用Mybatis config配置
创建configuration.xml
1 2 3 4 5 6 7 8 | <? xml version = "1.0" encoding = "UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-////DTD SQL MAP Config 3.1//EN"
"http:///dtd/mybatis-3-config.dtd">
< configuration >
< settings >
< setting name = "callSettersOnNulls" value = "true" />
</ settings >
</ configuration >
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配置Mybatis的SqlSessionFactoryBean
1 2 3 4 5 6 | < bean id = "sqlSessionFactory" class = "org.mybatis.spring.SqlSessionFactoryBean" >
< property name = "dataSource" ref = "dataSource" />
< property name = "configLocation" value = "classpath:/META-INF/spring/configuration.xml" />
< property name = "mapperLocations"
value = "classpath:/META-INF/spring/mybatis/modelMap/*.xml" />
</ bean >
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在这种配置中,age将以null值映射到map中。
如果想要配置age的默认值,则可以建立一个类,实现Mybatis的TypeHandler接口
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | public class EmptyStringIfNull implements TypeHandler<String> {
@Override
public String getResult(ResultSet rs, String columnName) throws SQLException {
return (rs.getString(columnName) == null ) ? "" : rs.getString(columnName);
}
@Override
public String getResult(ResultSet rs, int columnIndex) throws SQLException {
return (rs.getString(columnIndex) == null ) ? "" : rs.getString(columnIndex);
}
@Override
public String getResult(CallableStatement cs, int columnIndex) throws SQLException {
return (cs.getString(columnIndex) == null ) ? "" : cs.getString(columnIndex);
}
@Override
public void setParameter(PreparedStatement ps, int arg1, String str, JdbcType jdbcType) <span style= "line-height:1.5;font-size:9pt;" > throws SQLException {</span><span style= "line-height:1.5;font-size:9pt;" > }</span><span style= "line-height:1.5;font-size:9pt;" >}</span>
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继续在resultMap中使用,即可配置age的默认值(上述代码中age的默认值为"")
1 2 3 4 5 | < resultMap id = "list" type = "java.util.LinkedHashMap" >
< result property = "name" column = "name" />
< result property = "sex" column = "sex" />
< result property = "age" column = "age" typeHandler = "com.demo.EmptyStringIfNull" />
</ resultMap >
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网上有些资料中提到可以使用 defaultValue 和 nullValue的配置,但是这中配置是ibatis的用法,在Mybatis中已经移除。
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