mybatis主從表關聯查詢,返回對象帶有集合屬性解析

主從表關聯查詢,返回對象帶有集合屬性

昨天有同事讓我幫著看一個問題,mybatis主從表聯合查詢,返回的對象封裝集合屬性。我先將出現的問題記錄一下,然後再講處理方法也簡單說明一下:

VersionResult為接收返回數據對象

get\set方法我這裡就省略瞭。

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;
	//記錄內容表的集合對象
	private List<UpdateRecordEntity> UpdateRecordEntityList;	
	}

UpdateRecordEntity為從表數據

同樣get\set方法我這裡就省略瞭。

@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寫法,這個是關鍵

 <!--跟新記錄表封裝的對象-->
 <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查詢語句

<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>

執行sql返回的數據

頁面調取接口

下面我將接口數據粘貼下來:

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

觀察code、createTimes、updateRecordEntityList三個屬性,會發現隻有code字段有值其餘的全部為null。分析這個是為啥呢?找點資料粘貼如下:

發現是sql數據和VersionResult的mapper.xml中映射關系有點問題,沒有對應起來。resultMap中必須將別名和上面resultMap對的上就行,很明顯sql返回數據的列明沒有和resultMap一一對應起來,因此有瞭以下對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>

數據顯示正常:

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

mybatis關聯查詢(對象嵌套對象)

Mybatis 查詢對象中嵌套其他對象的解決方法有兩種,

一種是用關聯另一個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>

一種聯合查詢 (一對一)的實現

但是這種方式有“N+1”的問題,不建議使用

 <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> 

以上就是兩種對象內嵌套對象查詢的實現。僅為個人經驗,希望能給大傢一個參考,也希望大傢多多支持WalkonNet。

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