我已經在MySQL數據庫中創建了以下兩個表格,只有必要的字段。
mysql> desc cars;
+--------------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+---------------------+------+-----+---------+----------------+
| car_id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| manufacturer | varchar(100) | YES | | NULL | |
+--------------+---------------------+------+-----+---------+----------------+
2 rows in set (0.03 sec)
mysql> desc bookings;
+------------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------------------+------+-----+---------+----------------+
| booking_id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| fk_car_id | bigint(20) unsigned | NO | MUL | NULL | |
| from_date | date | YES | | NULL | |
| to_date | date | YES | | NULL | |
+------------+---------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
在bookings
表booking_id
是主鍵和fk_car_id
爲外鍵引用cars
表的主鍵(car_id
)。
使用IN()
子查詢中的相應的JPA標準查詢轉到如下所示。
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Cars> criteriaQuery = criteriaBuilder.createQuery(Cars.class);
Metamodel metamodel = entityManager.getMetamodel();
Root<Cars> root = criteriaQuery.from(metamodel.entity(Cars.class));
Subquery<Long> subquery = criteriaQuery.subquery(Long.class);
Root<Bookings> subRoot = subquery.from(metamodel.entity(Bookings.class));
subquery.select(subRoot.get(Bookings_.fkCarId).get(Cars_.carId));
List<Predicate> predicates = new ArrayList<Predicate>();
ParameterExpression<Date> fromDate1 = criteriaBuilder.parameter(Date.class);
Predicate exp1 = criteriaBuilder.lessThanOrEqualTo(subRoot.get(Bookings_.fromDate), fromDate1);
ParameterExpression<Date> toDate1 = criteriaBuilder.parameter(Date.class);
Predicate exp2 = criteriaBuilder.greaterThanOrEqualTo(subRoot.get(Bookings_.toDate), toDate1);
Predicate and1 = criteriaBuilder.and(exp1, exp2);
ParameterExpression<Date> fromDate2 = criteriaBuilder.parameter(Date.class);
Predicate exp3 = criteriaBuilder.lessThanOrEqualTo(subRoot.get(Bookings_.fromDate), fromDate2);
ParameterExpression<Date> toDate2 = criteriaBuilder.parameter(Date.class);
Predicate exp4 = criteriaBuilder.greaterThanOrEqualTo(subRoot.get(Bookings_.toDate), toDate2);
Predicate and2 = criteriaBuilder.and(exp3, exp4);
ParameterExpression<Date> fromDate3 = criteriaBuilder.parameter(Date.class);
Predicate exp5 = criteriaBuilder.greaterThanOrEqualTo(subRoot.get(Bookings_.fromDate), fromDate3);
ParameterExpression<Date> toDate3 = criteriaBuilder.parameter(Date.class);
Predicate exp6 = criteriaBuilder.lessThanOrEqualTo(subRoot.get(Bookings_.toDate), toDate3);
Predicate and3 = criteriaBuilder.and(exp5, exp6);
Predicate or = criteriaBuilder.or(and1, and2, and3);
predicates.add(or);
subquery.where(predicates.toArray(new Predicate[0]));
criteriaQuery.where(criteriaBuilder.in(root.get(Cars_.carId)).value(subquery).not());
List<Cars> list = entityManager.createQuery(criteriaQuery)
.setParameter(fromDate1, new Date("2015/05/04"))
.setParameter(toDate1, new Date("2015/05/04"))
.setParameter(fromDate2, new Date("2015/05/06"))
.setParameter(toDate2, new Date("2015/05/06"))
.setParameter(fromDate3, new Date("2015/05/04"))
.setParameter(toDate3, new Date("2015/05/06"))
.getResultList();
它產生的興趣的下面的SQL查詢(基於Hibernate 4.3.6最終測試,但不應該有在這一背景下,平均ORM框架的任何差異)。
SELECT
cars0_.car_id AS car_id1_7_,
cars0_.manufacturer AS manufact2_7_
FROM
project.cars cars0_
WHERE
cars0_.car_id NOT IN (
SELECT
bookings1_.fk_car_id
FROM
project.bookings bookings1_
WHERE
bookings1_.from_date<=?
AND bookings1_.to_date>=?
OR bookings1_.from_date<=?
AND bookings1_.to_date>=?
OR bookings1_.from_date>=?
AND bookings1_.to_date<=?
)
括號上面查詢的WHERE
子句中的條件式在技術上完全多餘的,其只需要更好其中休眠無視可讀性 - 休眠不必考慮它們。
我個人然而,喜歡使用EXISTS
操作。因此,查詢可以如下重建。
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Cars> criteriaQuery = criteriaBuilder.createQuery(Cars.class);
Metamodel metamodel = entityManager.getMetamodel();
Root<Cars> root = criteriaQuery.from(metamodel.entity(Cars.class));
Subquery<Long> subquery = criteriaQuery.subquery(Long.class);
Root<Bookings> subRoot = subquery.from(metamodel.entity(Bookings.class));
subquery.select(criteriaBuilder.literal(1L));
List<Predicate> predicates = new ArrayList<Predicate>();
ParameterExpression<Date> fromDate1 = criteriaBuilder.parameter(Date.class);
Predicate exp1 = criteriaBuilder.lessThanOrEqualTo(subRoot.get(Bookings_.fromDate), fromDate1);
ParameterExpression<Date> toDate1 = criteriaBuilder.parameter(Date.class);
Predicate exp2 = criteriaBuilder.greaterThanOrEqualTo(subRoot.get(Bookings_.toDate), toDate1);
Predicate and1 = criteriaBuilder.and(exp1, exp2);
ParameterExpression<Date> fromDate2 = criteriaBuilder.parameter(Date.class);
Predicate exp3 = criteriaBuilder.lessThanOrEqualTo(subRoot.get(Bookings_.fromDate), fromDate2);
ParameterExpression<Date> toDate2 = criteriaBuilder.parameter(Date.class);
Predicate exp4 = criteriaBuilder.greaterThanOrEqualTo(subRoot.get(Bookings_.toDate), toDate2);
Predicate and2 = criteriaBuilder.and(exp3, exp4);
ParameterExpression<Date> fromDate3 = criteriaBuilder.parameter(Date.class);
Predicate exp5 = criteriaBuilder.greaterThanOrEqualTo(subRoot.get(Bookings_.fromDate), fromDate3);
ParameterExpression<Date> toDate3 = criteriaBuilder.parameter(Date.class);
Predicate exp6 = criteriaBuilder.lessThanOrEqualTo(subRoot.get(Bookings_.toDate), toDate3);
Predicate and3 = criteriaBuilder.and(exp5, exp6);
Predicate equal = criteriaBuilder.equal(root, subRoot.get(Bookings_.fkCarId));
Predicate or = criteriaBuilder.or(and1, and2, and3);
predicates.add(criteriaBuilder.and(or, equal));
subquery.where(predicates.toArray(new Predicate[0]));
criteriaQuery.where(criteriaBuilder.exists(subquery).not());
List<Cars> list = entityManager.createQuery(criteriaQuery)
.setParameter(fromDate1, new Date("2015/05/04"))
.setParameter(toDate1, new Date("2015/05/04"))
.setParameter(fromDate2, new Date("2015/05/06"))
.setParameter(toDate2, new Date("2015/05/06"))
.setParameter(fromDate3, new Date("2015/05/04"))
.setParameter(toDate3, new Date("2015/05/06"))
.getResultList();
它產生以下SQL查詢。
SELECT
cars0_.car_id AS car_id1_7_,
cars0_.manufacturer AS manufact2_7_
FROM
project.cars cars0_
WHERE
NOT (EXISTS (SELECT
1
FROM
project.bookings bookings1_
WHERE
(bookings1_.from_date<=?
AND bookings1_.to_date>=?
OR bookings1_.from_date<=?
AND bookings1_.to_date>=?
OR bookings1_.from_date>=?
AND bookings1_.to_date<=?)
AND cars0_.car_id=bookings1_.fk_car_id))
它返回相同的結果列表。
附加:
這裏subquery.select(criteriaBuilder.literal(1L));
,而使用像上的EclipseLink,EclipseLink的gets confused複雜的子查詢語句criteriaBuilder.literal(1L)
表達式和導致異常。因此,在EclipseLink上編寫複雜的子查詢時可能需要考慮到這一點。在這種情況下,只需選擇id
,如
subquery.select(subRoot.get(Bookings_.fkCarId).get(Cars_.carId));
與第一種情況一樣。注意:如果您在EclipseLink上運行上述表達式,您將在SQL查詢生成中看到odd behaviour,儘管結果列表將相同。
您也可以使用連接,後者在後端數據庫系統上效率更高,在這種情況下,您需要使用DISTINCT
篩選出可能的重複行,因爲您需要父表中的結果列表。如果詳細表中存在多個子行,則結果列表可能包含重複行 - bookings
對應的父行cars
。 我把它留給你。 :)這就是它在這裏。
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Cars> criteriaQuery = criteriaBuilder.createQuery(Cars.class);
Metamodel metamodel = entityManager.getMetamodel();
Root<Cars> root = criteriaQuery.from(metamodel.entity(Cars.class));
criteriaQuery.select(root).distinct(true);
ListJoin<Cars, Bookings> join = root.join(Cars_.bookingsList, JoinType.LEFT);
ParameterExpression<Date> fromDate1 = criteriaBuilder.parameter(Date.class);
Predicate exp1 = criteriaBuilder.lessThanOrEqualTo(join.get(Bookings_.fromDate), fromDate1);
ParameterExpression<Date> toDate1 = criteriaBuilder.parameter(Date.class);
Predicate exp2 = criteriaBuilder.greaterThanOrEqualTo(join.get(Bookings_.toDate), toDate1);
Predicate and1 = criteriaBuilder.and(exp1, exp2);
ParameterExpression<Date> fromDate2 = criteriaBuilder.parameter(Date.class);
Predicate exp3 = criteriaBuilder.lessThanOrEqualTo(join.get(Bookings_.fromDate), fromDate2);
ParameterExpression<Date> toDate2 = criteriaBuilder.parameter(Date.class);
Predicate exp4 = criteriaBuilder.greaterThanOrEqualTo(join.get(Bookings_.toDate), toDate2);
Predicate and2 = criteriaBuilder.and(exp3, exp4);
ParameterExpression<Date> fromDate3 = criteriaBuilder.parameter(Date.class);
Predicate exp5 = criteriaBuilder.greaterThanOrEqualTo(join.get(Bookings_.fromDate), fromDate3);
ParameterExpression<Date> toDate3 = criteriaBuilder.parameter(Date.class);
Predicate exp6 = criteriaBuilder.lessThanOrEqualTo(join.get(Bookings_.toDate), toDate3);
Predicate and3 = criteriaBuilder.and(exp5, exp6);
Predicate or = criteriaBuilder.not(criteriaBuilder.or(and1, and2, and3));
Predicate isNull = criteriaBuilder.or(criteriaBuilder.isNull(join.get(Bookings_.fkCarId)));
criteriaQuery.where(criteriaBuilder.or(or, isNull));
List<Cars> list = entityManager.createQuery(criteriaQuery)
.setParameter(fromDate1, new Date("2015/05/04"))
.setParameter(toDate1, new Date("2015/05/04"))
.setParameter(fromDate2, new Date("2015/05/06"))
.setParameter(toDate2, new Date("2015/05/06"))
.setParameter(fromDate3, new Date("2015/05/04"))
.setParameter(toDate3, new Date("2015/05/06"))
.getResultList();
它產生以下SQL查詢。
SELECT
DISTINCT cars0_.car_id AS car_id1_7_,
cars0_.manufacturer AS manufact2_7_
FROM
project.cars cars0_
LEFT OUTER JOIN
project.bookings bookingsli1_
ON cars0_.car_id=bookingsli1_.fk_car_id
WHERE
(
bookingsli1_.from_date>?
OR bookingsli1_.to_date<?
)
AND (
bookingsli1_.from_date>?
OR bookingsli1_.to_date<?
)
AND (
bookingsli1_.from_date<?
OR bookingsli1_.to_date>?
)
OR bookingsli1_.fk_car_id IS NULL
如可以注意到休眠提供商逆響應WHERE NOT(...)
的WHERE
子句中的條件語句。其他提供者也可能生成確切的WHERE NOT(...)
,但畢竟,這與問題中所寫的相同,併產生與以前情況相同的結果列表。
未指定右連接。因此,JPA提供者不必執行它們。他們大多不支持正確的連接。
所屬JPQL只是爲了完整性:)起見
的IN()
查詢:
SELECT c
FROM cars AS c
WHERE c.carid NOT IN (SELECT b.fkcarid.carid
FROM bookings AS b
WHERE b.fromdate <=?
AND b.todate >=?
OR b.fromdate <=?
AND b.todate >=?
OR b.fromdate >=?
AND b.todate <=?)
的EXISTS()
查詢:
SELECT c
FROM cars AS c
WHERE NOT (EXISTS (SELECT 1
FROM bookings AS b
WHERE (b.fromdate <=?
AND b.todate >=?
OR b.fromdate <=?
AND b.todate >=?
OR b.fromdate >=?
AND b.todate <=?)
AND c.carid = b.fkcarid))
最後一個使用左連接(帶有命名參數):
SELECT DISTINCT c FROM Cars AS c
LEFT JOIN c.bookingsList AS b
WHERE NOT (b.fromDate <=:d1 AND b.toDate >=:d2
OR b.fromDate <=:d3 AND b.toDate >=:d4
OR b.fromDate >=:d5 AND b.toDate <=:d6)
OR b.fkCarId IS NULL
以上所有JPQL語句都可以按照您已知的方法使用以下方法運行。
List<Cars> list=entityManager.createQuery("Put any of the above statements", Cars.class)
.setParameter("d1", new Date("2015/05/04"))
.setParameter("d2", new Date("2015/05/04"))
.setParameter("d3", new Date("2015/05/06"))
.setParameter("d4", new Date("2015/05/06"))
.setParameter("d5", new Date("2015/05/04"))
.setParameter("d6", new Date("2015/05/06"))
.getResultList();
當需要/需要時,用相應的索引/位置參數替換命名參數。
所有這些JPQL語句也生成與上述標準API生成的SQL語句相同的SQL語句。
我總是避免在這種情況下IN()
子查詢,尤其是在 使用MySQL。我會用IN()
子查詢,當且僅當它們 絕對必要的情況下,比如當我們需要確定 結果集或刪除的,如
SELECT * FROM table_name WHERE id IN (1, 2, 3, 4, 5);`
DELETE FROM table_name WHERE id IN(1, 2, 3, 4, 5);
靜態值列表上排列表等。
在這種情況下,我總是希望使用EXISTS
運算符進行查詢,因爲結果列表只涉及 基於另一個表中的條件的單個表。在這種情況下加入 將產生前面提到的重複行,需要使用DISTINCT
過濾掉 ,如上面其中一個查詢所示。
- 我最好使用連接,當要檢索的結果集是從多個數據庫表組合而成的 時 - 無論如何都必須使用。
一切都依賴於許多事情。這些都不是里程碑。
聲明:我對RDBMS知之甚少。
注:我已經使用了參數/超載棄用日期構造 - Date(String s)
與SQL查詢中的所有情況下,一個純粹的測試目的相關的索引/位置參數才避免了你已經知道的噪音的整個一塌糊塗java.util.SimpleDateFormat
。您也可以使用其他更好的API,如Joda Time(Hibernate支持它),java.sql.*
(這些是java.util.Date
的子類),Java 8中的Java Time(現在大部分不支持,除非定製),並且在需要/需要時。
希望有幫助。
有一點需要注意的是,您的日期條件總結爲'fromDate> ='2015-05-04'AND toDate <='2015-05-06''。 – RealSkeptic
謝謝,我會編輯它。它應該是一個動態的時間範圍。如果從2015-05-05到2015-05-07預訂汽車,當開始日期或結束日期或兩者都與現有預訂衝突時,不應預訂該汽車。 –