MyBatis-映射器中sql标签详解

sql标签用来定义可重复使用的sql语句片段

必要说明

  • #ibatis中表示参数引用
  • $ibatis中表示变量引用

sql标签候选属性说明

  • id
    sql标签的全局唯一标识;
  • databaseId
    ibatis全局配置中的databaseIdProvider标签呼应;
  • lang
    可自定义的第三方语言,一般不使用;

使用规范说明

  • 语法规范

    <sql id="sql_unique_id">         
    	sql_part_statement           
    	<include refid="other_var"/> 
    	...                          
    sql>                           
    
  • sql标签方案的选择

    • 直接使用字面量的方式
      <sql id="xxx">               
      	column_a,column_b,column_c
      sql>                       
      
    • 也可在sql语句中使用变量引用;
      此处示例使用的是表别名.
      注意,声明中的prefix是可自定义的,可以是任何合法的标识符
      <sql id="sql_tag_id">                                               
      	${prefix}.column_a, ${prefix}.column_b, ${prefix}.column_c
      sql>                                                       
      
      在增删改查标签引用使用
      <select id="xxx">                            
      	<include refid="sql_tag_id">     
      		...	               
      		<property name="prefix" value="prefix_value_inSql"/>
      		...
      	include>                               
      select>                                    
      
    • 嵌套使用sql标签
      这种形式会大大降低sql的可读性,一般不建议嵌套sql使用.
      <sql id="some_sql">                                      
      	...                                                  
      sql>                                                   
      <sql id="all_sql">                                       
      	...                                                  
      	<include refid="${include_sql}" />                   
      	${prefix}                                            
      	...                                                  
      sql>                                                   
      <select id="xxx">                                        
      	...                                                  
      	<include refid="all_sql">                            
      		<property name="include_sql" value="some_sql" /> 
      		<property name="prefix" value="prefix_value" />  
      	include>                                           
      	...                                                  
      select>                                                
      

代码测试sql标签说明

sql标签的使用步骤

  1. entity类对象,ibatis全局配置设置省略;
       CREATE TABLE `emp` (
       `id` int(11) NOT NULL AUTO_INCREMENT,
       `name` varchar(255) NOT NULL,
       `age` int(11) NOT NULL,
       `sex` int(4) NOT NULL,
       PRIMARY KEY (`id`)
       ) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=latin1
    
  2. mapper映射配置文件中配置需求;
    使用sql标签定义表的列名称
    <sql id="test_sql">                                            
    	${tbl}.id, ${tbl}.name, ${tbl}.age, ${tbl}.sex             
    sql>                                                         
    <select id="test_sql_tag0" resultType="siye.ibatis.entity.Emp">
    	SELECT                                                     
    	<include refid="test_sql">                                 
    		<property name="tbl" value="e" />                      
    	include>                                                 
    	FROM emp e                                                 
    select>                                                      
    
    使用sql标签定义表的表名变量
    <sql id="table_name">                                          
    	select * from ${tbl_name}                                  
    sql>                                                         
    <select id="test_sql_tag1" resultType="siye.ibatis.entity.Emp">
    	<include refid="table_name">                               
    		<property name="tbl_name" value="emp" />               
    	include>                                                 
    select>                                                      
    
    嵌套sql标签的使用
    <sql id="some_sql">                                            
    	select * from                                              
    sql>                                                         
    <sql id="all_sql">                                             
    	<include refid="${include_sql}">                           
    	include>                                                 
    	${tbl_name}                                                
    sql>                                                         
    <select id="test_sql_tag2" resultType="siye.ibatis.entity.Emp">
    	<include refid="all_sql">                                  
    		<property name="include_sql" value="some_sql" />       
    		<property name="tbl_name" value="emp" />               
    	include>                                                 
    select>                                                      
    
  3. mapper接口省略;
  4. 测试类中的主要代码;
    SqlSession session = sqlSessionFactory.openSession(true);
    try
    {
    	SqlTag dao = session.getMapper(SqlTag.class);
    
    	List<Emp> list0 = dao.test_sql_tag0();
    	log.info(list0.size());
    
    	List<Emp> list1 = dao.test_sql_tag1();
    	log.info(list1.size());
    
    	List<Emp> list2 = dao.test_sql_tag2();
    	log.info(list2.size());
    
    } finally
    {
    	session.close();
    }
    
  5. 输出结果部分截取;
    DEBUG 2019-01-08 15:39:46,893 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : ==>  Preparing: SELECT e.id, e.name, e.age, e.sex  FROM   emp e 
    DEBUG 2019-01-08 15:39:46,937 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : ==> Parameters: 
    TRACE 2019-01-08 15:39:46,960 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : <==    Columns: id, name, age, sex
    ...
    DEBUG 2019-01-08 15:39:46,971 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : <==      Total: 7
     INFO 2019-01-08 15:39:46,971 siye.ibatis.test.Test_mapperUse : 7
    DEBUG 2019-01-08 15:39:46,972 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : ==>  Preparing: select * from emp 
    DEBUG 2019-01-08 15:39:46,972 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : ==> Parameters: 
    TRACE 2019-01-08 15:39:46,973 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : <==    Columns: id, name, age, sex
    ...
    DEBUG 2019-01-08 15:39:46,978 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : <==      Total: 7
     INFO 2019-01-08 15:39:46,978 siye.ibatis.test.Test_mapperUse : 7
    DEBUG 2019-01-08 15:39:46,978 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : ==>  Preparing: select * from emp 
    DEBUG 2019-01-08 15:39:46,979 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : ==> Parameters: 
    TRACE 2019-01-08 15:39:46,980 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : <==    Columns: id, name, age, sex
    ...
    DEBUG 2019-01-08 15:39:46,986 org.apache.ibatis.logging.jdbc.BaseJdbcLogger : <==      Total: 7
     INFO 2019-01-08 15:39:46,986 siye.ibatis.test.Test_mapperUse : 7
    

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