前言

今天用JPA又把之前的防疫物資項目重構(gòu)了一遍哼御，遇到很多問題坯临，不過最終都解決了，JPA的學習之路還是很長...

遇到難題

1.聯(lián)表查詢（返回自定義實體類）

JPA確實很強大恋昼，簡單的CRUD用的簡直舒服~看靠，但是今天在使用聯(lián)表查詢的時候，遇到了很棘手的問題液肌。直接上代碼挟炬。

@Entity
@Table(name = "material_record_info",)
public class MaterialRecordDO implements Serializable {
private static final long serialVersionUID = 1642587292218800992L;

    private int recordId;
    private Integer receiveNumber;
    private String receiveReason;
    private Date receiveDateTime;
    private int mId;
    private int uId;

get/set方法我就省略了，這是外鍵表物資記錄表嗦哆，其中的mId和uId是另外兩張表的主鍵谤祖。但是最終想顯示給用戶的這樣的：

public class MaterialRecordVO {
    private int recordId; //記錄編號
    private int receiveNumber; // 領(lǐng)取數(shù)量
    private String receiveReason; //領(lǐng)取原因
    private Date receiveDateTime; //領(lǐng)取時間
    private String materialName; //防疫物資名稱
    private String userRealName; //用戶真實姓名

最終使用JPQL解決了問題，注意自定義實體類要有對應(yīng)的有參構(gòu)造函數(shù)吝秕，順序也必須一樣泊脐。

@Repository
public interface IMaterialRecordDAO extends JpaRepository<MaterialRecordDO, Integer>  {

    @Query("SELECT new co'm.apesource.epmrs_3.entity.MaterialRecordVO(a.recordId,a.receiveNumber,a.receiveReason,a.receiveDateTime,b.materialName,c.userRealName)" +
           "FROM MaterialRecordDO a " +
           "INNER JOIN MaterialInfo b ON a.mId = b.materialId" +
           "INNER JOIN UserInfo c ON a.uId = c.userId")
    List<MaterialRecordVO> listMaterialRecord();

2.聯(lián)表動態(tài)查詢（返回自定義實體類）

我看了看JpaspecificationExecutor實現(xiàn)動態(tài)查詢的，看不太懂烁峭，而且好像不能返回自定義實體類容客，搞了幾個小時秕铛，最終還是用MyBatis解決了（太香了...），一個項目既用MyBatis又用JPA是不是不好呢缩挑。但两。。

    // 按條件查詢物資領(lǐng)用記錄
    @Select("<script> " +
            "SELECT  record_id AS recordId,\n" +
            "               material_name AS materialName,\n" +
            "               user_real_name AS userRealName,\n" +
            "               receive_number AS receiveNumber,\n" +
            "               receive_reason AS receiveReason,\n" +
            "               receive_date_time AS receiveDateTime\n" +
            "        FROM material_record_info AS a\n" +
            "        INNER JOIN material_info AS b ON a.m_id = b.material_id\n" +
            "        INNER JOIN user_info AS c ON a.u_id = c.user_id\n" +
            "        <where>\n" +
            "           <if test='materialId != -1'>AND material_id = #{materialId}</if>\n" +
            "           <if test='userId != -1'>AND  user_id = #{userId}</if>\n" +
            "           <if test='receiveDateBegin != null and receiveDateEnd != null'>\n" +
            "               AND DATE_FORMAT(receive_date_time,'%Y-%m-%d') BETWEEN #{receiveDateBegin} AND #{receiveDateEnd}\n" +
            "           </if>\n" +
            "        </where>\n" +
            "        ORDER BY receive_date_time" +
            "</script> ")
    List<MaterialRecordVO> listMaterialRecordByCondition(MaterialRecordCondition recordCondition);

用這個記得加個<script>標簽供置，不然不能解析谨湘，很怪。

總結(jié)

剛剛上手使用SpringBoot重構(gòu)項目之后芥丧，會有一些面試相關(guān)的問題吧
1.使用Spring框架的好處
2.注解怎么使用或者原理
3.Spring怎么實現(xiàn)Bean的管理的
4.Spring容器初始化過程
5.IOC思想

這些東西明天再做一個整理紧阔。