MyBatis if子句

Question

我尝试遵循MyBatis中的if子句，但得到以下异常，请帮助我识别这里的问题。

public class Student{

private Integer studId;
private String name;
private String email;
private Date dob;
}

映射

<select id="searchStudent" parameterType="hashmap" resultMap="StudentResult">
    <![CDATA[
    SELECT * FROM STUDENTS
    WHERE 1 = 1 

    <if test="studId != null">
    AND STUD_ID= #{studId}
    </if>

    <if test="name != null">
    AND NAME like #{name}
    </if>

    ]]>
</select>

我得到的异常：

Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL   syntax; check the manual that corresponds to your MySQL server version for the right syntax   to use near 'test="studId != null">
    AND STUD_ID= 1
    </if>

    <if test="name != null">
    ' at line 4
### The error may exist in StudentMapper.xml
### The error may involve com.maventest.mytest.StudentMapper.searchStudent-Inline
### The error occurred while setting parameters
### SQL: SELECT * FROM STUDENTS   WHERE 1 = 1       <if test="studId != null">   AND STUD_ID= ?   </if>      <if test="name != null">   AND NAME like ?   </if>
### Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'test="studId != null">
    AND STUD_ID= 1
    </if>

    <if test="name != null">
    ' at line 4
at    org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23)

Answer 1

删除<![CDATA[和]]>，因为这将转义所有查询，并且mybatis根本不会处理它，因此if将作为数据库查询的一部分逐字传递。

<select id="searchStudent" parameterType="hashmap" resultMap="StudentResult">
  SELECT * FROM STUDENTS
  WHERE 1 = 1 

  <if test="studId != null">
    AND STUD_ID= #{studId}
  </if>

  <if test="name != null">
    AND NAME like #{name}
  </if>

</select>

Answer 2

CDATA节用于转义包含字符的文本块，否则这些字符将被视为标记ORACLE定义。

有时，我们需要它，特别是当我们有一个带有<，>，<>等标记的where条件时。

​

<![CDATA[ SELECT * FROM STUDENTS WHERE 1 = 1 ]]>
<if test="studId != null">
<![CDATA[ AND STUD_ID= #{studId} ]]>
</if>

<if test="name != null">
**<![CDATA[ AND COD_PER <> 'ASSU' ]]>**
</if>

​

将它添加到带有标记问题的行上也是可行的。