在Mybatis中association標(biāo)簽多層嵌套的問題
association標(biāo)簽多層嵌套問題
mybatis里查詢使用嵌套association標(biāo)簽時,發(fā)現(xiàn)內(nèi)層的association查詢的結(jié)果一直為null
排查
- 檢查sql執(zhí)行情況,發(fā)現(xiàn)有數(shù)據(jù)返回,排除
- 檢查property的值是否和pojo中的對應(yīng),值一致,排除
- 檢查column的值是否和數(shù)據(jù)庫的相對應(yīng),相對應(yīng),排除
那么應(yīng)該是mybatis沒有把數(shù)據(jù)映射到位了,經(jīng)過排查是association中columnPrefix被不對應(yīng)
<resultMap id="BaseResultMap" type="a.b.c.d.e"> ? ? <id column="id" property="id" /> ? ? <result property="workTime" column="work_time" /> ? ? <result property="model" column="model" /> ? ? <result property="status" column="status" /> ? ? <association property="interfaceUpstream" javaType="interfaceUpstream" columnPrefix="ui_"> ? ? ? <id column="id" property="id" /> ? ? ? <result property="interfaceName" column="interface_name" /> ? ? ? <result property="interfaceType" column="interface_type" /> ? ? ? <result property="frequency" column="frequency" /> ? ? ? <result property="address" column="address" /> ? ? ? <result property="templateOrSql" column="template_or_sql" /> ? ? ? <result property="status" column="status" /> ? ? ? <association property="systemInfo" javaType="SystemInfo" columnPrefix="sys_"> ? ? ? ? <id column="id" property="id"/> ? ? ? ? <result property="systemName" column="system_name"/> ? ? ? ? <result property="systemNameEN" column="system_name_en"/> ? ? ? ? <result property="belong" column="belong"/> ? ? ? ? <result property="status" column="status"/> ? ? ? </association> ? ? ? <association property="serverInfo" javaType="ServerInfo" columnPrefix="ser_"> ? ? ? ? <id column="id" property="id"/> ? ? ? ? <result property="ftpIp" column="ftp_ip"/> ? ? ? ? <result property="ftpPort" column="ftp_port"/> ? ? ? ? <result property="ftpAccount" column="ftp_account"/> ? ? ? ? <result property="ftpPassword" column="ftp_password"/> ? ? ? </association> ? ? </association> ? </resultMap>
<sql id="base_select"> ? ? SELECT ?? ?ii.Id, ?? ?ii.model, ?? ?ii.status, ?? ?ii.work_time, ?? ?ui.id AS ui_id, ?? ?ui.interface_name AS ui_interface_name, ?? ?ui.interface_type AS ui_interface_type, ?? ?ui.frequency AS ui_frequency, ?? ?ui.address AS ui_address, ?? ?ui.template_or_sql AS ui_template_or_sql, ?? ?ui.status AS ui_status, ?? ?sys.id AS sys_id, ?? ?sys.system_name AS sys_system_name, ?? ?sys.system_name_en AS sys_system_name_en, ?? ?sys.belong AS sys_belong, ?? ?sys.status AS sys_status, ?? ?ser.id AS ser_id, ?? ?ser.ftp_ip AS ser_ftp_ip, ?? ?ser.ftp_port AS ser_ftp_port, ?? ?ser.ftp_account AS ser_ftp_account, ?? ?ser.ftp_password AS ser_ftp_password ? </sql>
從代碼上看沒有什么問題
原因是association在進行多層嵌套時,mybatis會將外層association的columnPrefix值與內(nèi)層的進行并合,
如外層columnPrefix值位ui_, 內(nèi)層為sys_, 那么在SQL中就不能這樣 sys.id AS sys_id 了,需要將ui_前綴加上,變成 sys.id AS ui_sys_id ,這樣mybatis在匹配的時候才會將數(shù)據(jù)映射到對應(yīng)association上
正常代碼如下
SELECT ?? ?ii.Id, ?? ?ii.model, ?? ?ii.status, ?? ?ii.work_time, ?? ?ui.id AS ui_id, ?? ?ui.interface_name AS ui_interface_name, ?? ?ui.interface_type AS ui_interface_type, ?? ?ui.frequency AS ui_frequency, ?? ?ui.address AS ui_address, ?? ?ui.template_or_sql AS ui_template_or_sql, ?? ?ui.status AS ui_status, ?? ?sys.id AS ui_sys_id, ?? ?sys.system_name AS ui_sys_system_name, ?? ?sys.system_name_en AS ui_sys_system_name_en, ?? ?sys.belong AS ui_sys_belong, ?? ?sys.status AS ui_sys_status, ?? ?ser.id AS ui_ser_id, ?? ?ser.ftp_ip AS ui_ser_ftp_ip, ?? ?ser.ftp_port AS ui_ser_ftp_port, ?? ?ser.ftp_account AS ui_ser_ftp_account, ?? ?ser.ftp_password AS ui_ser_ftp_password
問題解決!
association集合嵌套
學(xué)了一下mybatis的查詢返回值的集合嵌套,先查了查官網(wǎng):
這個返回集合有什么用呢
舉個例子三張表
hr_job_department
hr_job_position
第三張表里在表示部門和職位的時候只用了上面兩張表的主鍵
但是查詢的時候,希望表示下面這樣的結(jié)果
所以返回值是不止一個對象,這樣就用到了集合嵌套
<resultMap id="userInfoMap" type="com.advancedc.hrsys.entity.UserInfo"> <id column="id" property="id" /> <result column="name" property="name" /> <result column="gender" property="gender" /> <result column="id_card" property="idCard" /> <result column="is_married" property="isMarried" /> <result column="phone" property="phone" /> <result column="priority" property="priority" /> <result column="entry_time" property="entryTime" /> <result column="full_time" property="fullTime" /> <result column="created_time" property="createdTime" /> <result column="edited_time" property="editedTime" /> <association property="jobDepartment" column="id" javaType="com.advancedc.hrsys.entity.JobDepartment"> <id column="jdid" property="id" /> <result column="jdname" property="name" /> </association> <association property="jobPosition" column="id" javaType="com.advancedc.hrsys.entity.JobPosition"> <id column="jpid" property="id" /> <result column="jpname" property="name" /> </association> </resultMap>
只需要知道:
(1)column表示數(shù)據(jù)庫字段
(2)property表示Java里的值
而且我這里的主鍵都是id所以會出現(xiàn)重名的情況,在SQL語句里,查詢時就要賦予別名才能加以區(qū)分,返回結(jié)果resultMap就如上圖所示
<select id="queryUserInfoBySomeone" resultMap="userInfoMap" resultType="com.advancedc.hrsys.entity.UserInfo"> SELECT ui.id, ui.name, ui.gender, ui.id_card, ui.is_married, ui.department_id, ui.position_id, ui.phone, ui.priority, ui.entry_time, ui.full_time, ui.created_time, ui.edited_time, jd.id jdid, jd.name jdname, jp.id jpid, jp.name jpname FROM hr_user_info ui INNER JOIN hr_job_department jd ON ui.department_id=jd.id INNER JOIN hr_job_position jp ON ui.position_id=jp.id <where> <if test="someone.id>0"> and ui.id = #{someone.id} </if> <if test="someone.gender!=null"> and ui.gender = #{someone.gender} </if> <if test="someone.name!=null"> and ui.name = #{someone.name} </if> <if test="someone.idCard!=null"> and ui.id_card = #{someone.idCard} </if> <if test="someone.isMarried!=null"> and ui.is_married = #{someone.isMarried} </if> <if test="someone.jobDepartment!=null and someone.jobDepartment.id!=null"> and ui.department_id = #{someone.jobDepartment.id} </if> <if test="someone.jobPosition!=null and someone.jobPosition.id!=null"> and ui.position_id = #{someone.jonPosition.id} </if> <if test="someone.phone!=null"> and ui.phone = #{someone.phone} </if> <if test="someone.entryTime!=null"> and ui.entry_time = #{someone.entryTime} </if> <if test="someone.fullTime!=null"> and ui.full_time = #{someone.fullTime} </if> </where> </select>
上圖用了INNER JOIN來查詢看上去挺簡潔的,有一種不簡潔的寫法如下,雖然也能得到結(jié)果,但是不知道性能對比如何
SELECT ui.id, ui.name, ui.gender, ui.id_card, ui.is_married, ui.department_id, ui.position_id, ui.phone, ui.priority, ui.entry_time, ui.full_time, ui.created_time, ui.edited_time, (select id jdid from hr_job_department jd where jd.id=ui.department_id) jdid, (select name jdname from hr_job_department jd where jd.id=ui.department_id) jdname, (select id jpid from hr_job_position jp where jp.id=ui.position_id) jpid, (select name jpname from hr_job_position jp where jp.id=ui.position_id) jpname FROM hr_user_info ui;
以上為個人經(jīng)驗,希望能給大家一個參考,也希望大家多多支持腳本之家。
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