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mybatis关联查询返回对象带集合

瘦_猴 人气:0

主从表关联查询,返回对象带有集合属性

昨天有同事让我帮着看一个问题,mybatis主从表联合查询,返回的对象封装集合属性。我先将出现的问题记录一下,然后再讲处理方法也简单说明一下:

VersionResult为接收返回数据对象

get\set方法我这里就省略了。

public class VersionResult extends BaseResult implements Serializable{
	private Integer id;
	private String code;
	@JsonFormat(pattern = "yyyy-MM-dd HH:mm", timezone = "GMT+8")
	private Date createTimes;
	//记录内容表的集合对象
	private List<UpdateRecordEntity> UpdateRecordEntityList;	
	}

UpdateRecordEntity为从表数据

同样get\set方法我这里就省略了。

@Table(name = "z_update_record")
public class UpdateRecordEntity extends BaseEntity {
    @Id
    private Integer id;
    @Column(name = "version_id")
    private Integer versionId;
    @Column(name = "module_name")
    private String moduleName;
    @Column(name = "update_content")
    private String updateContent;
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm", timezone = "GMT+8")
    @Column(name = "create_time")
    private Date createTime;
    @Column(name = "is_delete")
    private Integer isDelete;
    }

mapper.xml写法,这个是关键

 <!--跟新记录表封装的对象-->
 <resultMap id="BaseResultMap" type="com.wangtiansoft.wisdomedu.persistence.result.server.VersionResult">
     <id column="id" property="id" jdbcType="INTEGER"/>
     <result column="code" property="code" />
     <result column="create_time" property="createTimes" />
     <collection property="UpdateRecordEntityList" ofType="com.wangtiansoft.wisdomedu.persistence.entity.UpdateRecordEntity">
         <id property="id" column="id"/>
         <result property="versionId" column="version_id"/>
         <result property="moduleName" column="module_name"/>
         <result property="updateContent"  column="update_content"/>
         <result property="createTime" column="create_time"/>
         <result property="isDelete" column="is_delete"/>
         <result property="tenantId" column="tenant_id"/>
     </collection>
 </resultMap>

sql查询语句

<select id="selectVersionList" parameterType="map" resultMap="BaseResultMap">
     SELECT
         z.`code`,
         z.create_time createTimes,
         zur.module_name moduleName,
         zur.update_content updateContent,
         zur.create_time createTime
     FROM
      	 z_version z
     LEFT JOIN z_update_record zur ON z.id = zur.version_id
     WHERE
         z.tenant_id = #{tenantId}
         AND z.is_delete = 0
         AND z.is_disabled = 0
         AND zur.tenant_id = #{tenantId}
         AND zur.is_delete = 0
         AND YEAR(z.create_time)=YEAR(#{date})
         ORDER by z.create_time desc
 </select>

执行sql返回的数据

页面调取接口

下面我将接口数据粘贴下来:

{
	"code": "0",
	"msg": "",
	"data": [{
		"id": null,
		"code": "1419",
		"createTimes": null,
		"updateRecordEntityList": []
	}, {
		"id": null,
		"code": "开发修改1111",
		"createTimes": null,
		"updateRecordEntityList": []
	}, {
		"id": null,
		"code": "开发修改1111",
		"createTimes": null,
		"updateRecordEntityList": []
	}, {
		"id": null,
		"code": "开发修改1111",
		"createTimes": null,
		"updateRecordEntityList": []
	}, {
		"id": null,
		"code": "开发修改1111",
		"createTimes": null,
		"updateRecordEntityList": []
	}]
}

观察code、createTimes、updateRecordEntityList三个属性,会发现只有code字段有值其余的全部为null。分析这个是为啥呢?找点资料粘贴如下:

发现是sql数据和VersionResult的mapper.xml中映射关系有点问题,没有对应起来。resultMap中必须将别名和上面resultMap对的上就行,很明显sql返回数据的列明没有和resultMap一一对应起来,因此有了以下对xml文件的修改:

   <resultMap id="BaseResultMap" type="com.wangtiansoft.wisdomedu.persistence.result.server.VersionResult">
        <id column="id" property="id" jdbcType="INTEGER"/>
        <result column="code" property="code" />
        <result column="createTimes" property="createTimes" />
        <collection property="UpdateRecordEntityList" ofType="com.wangtiansoft.wisdomedu.persistence.entity.UpdateRecordEntity">
            <id property="id" column="id"/>
            <result property="moduleName" column="moduleName"/>
            <result property="updateContent"  column="updateContent"/>
            <result property="createTime" column="createTime"/>
        </collection>
    </resultMap>

数据显示正常:

{
    "code": "0",
    "msg": "",
    "data": [{
        "code": "1419",
        "createTimes": "2019-09-02 00:00",
        "updateRecordEntityList": [{
            "moduleName": "安达市大所",
            "updateContent": "1321321",
            "createTime": "2019-09-02 10:17"
        }]
    }, {
        "code": "开发修改1111",
        "createTimes": "2019-05-07 00:00",
        "updateRecordEntityList": [{
            "moduleName": "平台111111",
            "updateContent": "平台版本第一次更新1",
            "createTime": "2019-08-15 15:07"
        }]
    }, {
        "code": "开发修改1111",
        "createTimes": "2019-05-07 00:00",
        "updateRecordEntityList": [{
            "moduleName": "111",
            "updateContent": "111",
            "createTime": "2019-08-16 11:16"
        }]
    }, {
        "code": "开发修改1111",
        "createTimes": "2019-05-07 00:00",
        "updateRecordEntityList": [{
            "moduleName": "515",
            "updateContent": "5155",
            "createTime": "2019-08-21 17:29"
        }]
    }, {
        "code": "开发修改1111",
        "createTimes": "2019-05-07 00:00",
        "updateRecordEntityList": [{
            "moduleName": "2222",
            "updateContent": "第二次更新",
            "createTime": "2019-08-22 14:23"
        }]
    }]
}

mybatis关联查询(对象嵌套对象)

Mybatis 查询对象中嵌套其他对象的解决方法有两种,

一种是用关联另一个resultMap的形式

如下:

<association property="office"  javaType="Office" resultMap="officeMap"/>
<mapper namespace="com.dixn.oa.modules.sys.dao.RoleDao">
    
   <resultMap type="Office" id="officeMap">
        <id property="id" column="id" />
        <result property="name" column="office.name" />
        <result property="code" column="office.code" />
    </resultMap>
    
    <resultMap id="roleResult" type="Role">
        <id property="id" column="id" />
        <result property="name" column="name" />
        <result property="enname" column="enname" />
        <result property="roleType" column="roleType" />
        <result property="dataScope" column="dataScope" />
        <result property="remarks" column="remarks" />
        <result property="useable" column="useable" />
        <association property="office"  javaType="Office" resultMap="officeMap"/>
        <collection property="menuList" ofType="Menu">
            <id property="id" column="menuList.id" />
        </collection>
        <collection property="officeList" ofType="Office">
            <id property="id" column="officeList.id" />
        </collection>
    </resultMap>
    <sql id="roleColumns">
        a.id,
        a.office_id AS "office.id",
        a.name,
        a.enname,
        a.role_type AS roleType,
    a.data_scope AS dataScope,
    a.remarks,
    a.create_by AS "createBy.id",
    a.create_date,
    a.update_by AS "updateBy.id",
    a.update_date,
    a.del_flag,
        o.name AS "office.name",
        o.code AS "office.code",
        a.useable AS useable,
        a.is_sys AS sysData
    </sql>
<select id="get" resultMap="roleResult">
    SELECT
    <include refid="roleColumns"/>
    rm.menu_id AS "menuList.id",
    ro.office_id AS "officeList.id"
    FROM sys_role a
    JOIN sys_office o ON o.id = a.office_id
    LEFT JOIN sys_role_menu rm ON rm.role_id = a.id
    LEFT JOIN sys_role_office ro ON ro.role_id = a.id
    WHERE a.id = #{id}
</select>

一种联合查询 (一对一)的实现

但是这种方式有“N+1”的问题,不建议使用

 <resultMap id="roleResult" type="Role">
        <id property="id" column="id" />
        <result property="name" column="name" />
        <result property="enname" column="enname" />
        <result property="roleType" column="roleType" />
        <result property="dataScope" column="dataScope" />
        <result property="remarks" column="remarks" />
        <result property="useable" column="useable" />
        <association property="office"  javaType="Office"     column="id" select="getOfficeById"/>
        <collection property="menuList" ofType="Menu">
            <id property="id" column="menuList.id" />
        </collection>
        <collection property="officeList" ofType="Office">
            <id property="id" column="officeList.id" />
        </collection>
    </resultMap>
    <select id="getOfficeById"  resultType="Office">
        select o.name AS "office.name",o.code AS "office.code" from sys_office o where o.id = #{id}
    </select> 

以上就是两种对象内嵌套对象查询的实现。仅为个人经验,希望能给大家一个参考,也希望大家多多支持。

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