SpringDataJPA筆記(13)-Union查詢

SpringDataJPA筆記(13)-Union查詢

在JPA中，對Union查詢可以通過兩種方式，一種是通過Inheritance的註解來實現，一種是通過子查詢來實現，個人覺得子查詢的方式更加靈活一點

來看具體的demo

首先是第一種通過Inheritance的註解

先設置一個基類，包含了要查詢出來的屬性，這個類並不會生成實際的表

需要注意一點 如果使用這個註解，id不能使用自增長，因爲id在多個表中需要保證唯一性

@Data
@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class UnionBaseEntity implements Serializable {

    private static final long serialVersionUID = 1846463590189371497L;
    @Id
    private Long id;

    @Column(name = "union_name")
    private String unionName;

    @Column(name = "union_age")
    private Integer unionAge;
}

然後是兩張實際要union查詢的表

@Data
@Entity
@EqualsAndHashCode(callSuper = true)
@Table(name = "union_one_tb")
public class UnionOneEntity extends UnionBaseEntity {

    @Column(name = "union_one")
    private String unionOne;

}

@Data
@Entity
@EqualsAndHashCode(callSuper = true)
@Table(name = "union_two_tb")
public class UnionTwoEntity extends UnionBaseEntity {

    @Column(name = "union_two")
    private String unionTwo;

}

然後配置相關的repository接口類

public interface UnionBaseRepository extends JpaRepository<UnionBaseEntity, Long>, JpaSpecificationExecutor<UnionBaseEntity>, Serializable {
}

public interface UnionOneRepository extends JpaRepository<UnionOneEntity, Long>, JpaSpecificationExecutor<UnionOneEntity>, Serializable {
}

public interface UnionTwoRepository extends JpaRepository<UnionTwoEntity, Long>, JpaSpecificationExecutor<UnionTwoEntity>, Serializable {
}

先添加幾條數據，查看數據庫，確實只有兩張表

再查看兩張表的數據

編寫controller，查詢數據

    @GetMapping("/list/base")
    public List<UnionBaseEntity> listBase() {
        return unionBaseRepository.findAll();
    }

從swagger頁面調用listBase接口

這裏會發現一個問題，id相同的兩條記錄被覆蓋了，所以使用這個註解的時候，需要保證id的唯一性

第二種通過子查詢的模式

@Data
@Entity
@Immutable
@Subselect("select concat(\'one_\', a.id) as id, a.union_name as union_name, a.union_age as union_age from union_one_tb a " +
        "union all select concat(\'two_\', b.id) as id, b.union_name as union_name, b.union_age as union_age from union_two_tb b ")
@Synchronize({"union_one_tb", "union_two_tb"})
public class UnionSubEntity implements Serializable {

    private static final long serialVersionUID = -3795682088296075408L;
    @Id
    private String id;

    @Column(name = "union_name")
    private String unionName;

    @Column(name = "union_age")
    private Integer unionAge;
}

public interface UnionSubRepository extends JpaRepository<UnionSubEntity, String>, JpaSpecificationExecutor<UnionSubEntity>, Serializable {
}

編寫controller

    @GetMapping("/list/sub")
    public List<UnionSubEntity> listSub(){
        return unionSubRepository.findAll();
    }

從swagger頁面調用listSub接口，查看數據

子查詢的方式更爲靈活，特別是對於聯合查詢的數據沒有統一的唯一主鍵時

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