mybatis学习笔记--常见的错误

原文来自：《mybatis学习笔记--常见的错误》

1. 
   

昨天刚学了下mybatis,用的是3.2.2的版本,在使用过程中遇到了些小问题,现总结如下,会不断更新.

1.没有在configuration.xml配置对应的sql配置文件

错误:

Error updating database. Cause:  java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for ***Mapper.*** Cause: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for ***Mapper.***
解决方法:

在configuration.xml配置文件中引用对应的sql配置文件

<mappers>
    <mapper resource="esd/db/mapper/ResumeMapper.xml" />
mappers>

2.同一sql配置文件中id重复

错误:

Cause: org.apache.ibatis.builder.BuilderException:  Error parsing SQL Mapper Configuration. Cause: java.lang.RuntimeException: Error parsing Mapper XML. Cause: java.lang.IllegalArgumentException: Mapped Statements collection already contains value for GeographyMapper.getByCode
两个sql语句的id重复了,就会报这个错.

<select id="getByCode" resultType="Geography"
    parameterType="java.lang.String">
    select * from Geography where code = ${code}
select>


<select id="getByCode" resultType="Geography"
    parameterType="java.lang.String">
    select * from Geography where fullName = ${fullName}
select>

解决方法:

修改其中的一个id就ok了.
3.mapper配置文件中为bean类配置的属性没有在对应的bean类中找到对应的字段

错误:

Error updating database.  Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'education' in 'class esd.bean.Personal'
Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'education' in 'class esd.bean.Personal'

            <if test="education != null and education != ''">
                education = #{education},
            if>

解决方法:

在mapper配置文件中删除多配置的属性/或则在自己的bean类中补全该字段

4.标签中不支持 && 符号

错误:

The entity name must immediately follow the '&' in the entity reference

解析不了 && 是什么东东

<update id="update" parameterType="Geography">
        update Geography
        <trim prefix="set" suffixOverrides=",">
            <if test="code != null && code !=''">
                code=#{code},
            if>
            <if test="name != null && name != ''">
                name=#{name},
            if>
        trim>
        where id= #{id}
    update>

解决方法:使用正确的语法咯,别用&&,用and

    <update id="update" parameterType="Geography">
        update Geography
        <trim prefix="set" suffixOverrides=",">
            <if test="code != null and code !=''">
                code=#{code},
            if>
            <if test="name != null and name != ''">
                name=#{name},
            if>
        trim>
        where id= #{id}
    update>

5.返回结果类型写错

由于我的项目配置原因, debug 输出信息中没有报错, 但是项目就是启动不起来, 所以没能截到错误信息提示, 以后遇到会补上

具体说就是: 如果自定义了返回的结果集, 返回的类型一定要是resultMap类型,(下面是错误示例) 如下

    <resultMap id="ResultArea" type="Area">
        <id column="a_code" property="code" />
        <result column="a_name" property="name" />
        <result column="a_pyName" property="pyName" />
        <result column="a_abbr" property="abbr" />
        <result column="a_mark" property="mark" />
    resultMap>


    <resultMap id="ResultParameter" type="Parameter">
        <id column="p_id" property="id" />
        <result column="p_name" property="name" />
        <result column="p_value" property="value" />
        <result column="p_type" property="type" />
        <result column="p_mark" property="mark" />
        <association property="area" javaType="Parameter" resultMap="ResultArea" />
    resultMap>


    <select id="getById" resultType="ResultParameter" parameterType="int">
        select p.id as p_id, p.name as p_name, p.value as p_value, p.type as p_type, p.mark as p_mark,
                a.code as a_code, a.name as a_name, a.pyname as a_pyName, a.abbr as a_abbr, a.mark as a_mark
        from parameter as p, area as a
        where p.acode = a.code and id = #{id}
    select>

常用在表连接查询中.

如上例中, 我定义了'ResultParameter'的结果集,  那么下面表连接查询的时候,如果返回的是表连接查询结果, 那么一定要使用 resultMap="ResultParameter", 否则万一提示信息中没有显示出来, 要费些时间才能找出来.

6. 标签顺序写错

错误:

The content of element type "resultMap" must match "(constructor?,id*,result*,association*,collection*,discriminator?)".

下午的时候无意中遇到这个错误, 下面是错误代码:

<resultMap id="ResultMenu" type="com.esd.hesf.model.Menu">
    <id column="id" property="id" jdbcType="CHAR" />
    <result column="text" property="text" jdbcType="VARCHAR" />
    <result column="iconcls" property="iconcls" jdbcType="VARCHAR" />
    <association property="permissionType" javaType="com.esd.hesf.model.PermissionType" resultMap="ResultPermissionType"/>
    <result column="update_time" property="updateTime" jdbcType="TIMESTAMP" />
resultMap>

在标签, 一定要放在这组标签最下面.  如下:

<resultMap id="ResultMenu" type="com.esd.hesf.model.Menu">
    <id column="id" property="id" jdbcType="CHAR" />
    <result column="text" property="text" jdbcType="VARCHAR" />
    <result column="iconcls" property="iconcls" jdbcType="VARCHAR" />
    <result column="update_time" property="updateTime" jdbcType="TIMESTAMP" />
    <association property="permissionType" javaType="com.esd.hesf.model.PermissionType" resultMap="ResultPermissionType"/>
resultMap>

7.多写了if判断

错误:

org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'year' in 'class java.lang.String'

下面是代码:

dao层方法

/**
     * 查询审核报表情况--按公司类型查
     * @return
     */
    List retrieveReportByCompanyType(String year);

mapper配置文件

    <select id="retrieveReportByCompanyType" parameterType="java.lang.String" resultMap="ReportViewModel">
        select
            <include refid="report_column_list"/>
        from audit_company_view
        <where>
            <if test="year != null and year != ''">
                au_year = #{year,jdbcType=CHAR}
            if>
        where>
        group by t_id
    select>

一般这个错是指参数parameterType类型的字段 没有get, set方法, 我只是传个String类型的参数, so 刚遇到这个问题的时候, 有点摸不着头脑, 怎么会报这个错呢? 原来问题出现在配置文件中:

<if test="year != null and year != ''">

mybatis自动将if判断中的字段默认为传进来的parameterType类型的字段了... so....只要将这个if判断去掉即可.

<select id="retrieveReportByCompanyType" parameterType="java.lang.String" resultMap="ReportViewModel">
    select
        <include refid="report_column_list"/>
    from audit_company_view
    <where>
            au_year = #{year,jdbcType=CHAR}
    where>
    group by t_id
select>

那问题出来了, 我怎么判断传进来的单个字符串是否为空值呢? 这是否是mybatis的一个小bug呢?  答案尚在查找中, 有了会第一时间贴上来的.