熟悉了mybatis的靈活，可能你對(duì)他的動(dòng)態(tài)查詢很喜歡，表示各種sql都能勝任。初步接觸jpa時(shí)，你會(huì)各種吐槽，不如mybatis來(lái)的方便。其實(shí)jpa也能幫你完成你的各種需求，至于編寫的復(fù)雜度，那可能就仁者見(jiàn)仁智者見(jiàn)智了。習(xí)慣了，其實(shí)也一樣了。

代碼放github和碼云了：spring-data/github spring-data/碼云

save操作(含merge操作，即update也在save里)

• save方法會(huì)預(yù)檢查該entity是否持久化，isNew會(huì)判斷該對(duì)象的Id類型 是否實(shí)現(xiàn)Persistable或EntityInformation進(jìn)行重寫isNew方法，如果Id是Number類型，直接判斷value==0 true 執(zhí)行entityManager.persist 否則執(zhí)行entityManager.merge()

  /**
   * save方法會(huì)預(yù)檢查該entity是否持久化，isNew會(huì)判斷該對(duì)象的Id類型 是否實(shí)現(xiàn)Persistable或EntityInformation進(jìn)行
   * 重寫isNew方法，如果Id是Number類型，直接判斷value==0 true 執(zhí)行entityManager.persist 否則執(zhí)行entityManager.merge()
   */
  @Test
  public void insert() {
    Customer customer = new Customer();
    customer.setName("lk");
    customer.setEmail("spring.jpa@163.com");
    customer.setAddress("Shanghai PuDong Area XueYe Road");
    customer.setPhone("13699999999");
    //這里保存以后customer的id會(huì)被填充為保存后entity的id
    Customer savedEntity = customerRepository.save(customer);
    //保存并立即刷新數(shù)據(jù)庫(kù)，由于customer以及提供id，會(huì)執(zhí)行merge方法進(jìn)行保存
//    Customer savedAndFlush = customerRepository.saveAndFlush(customer);
    List<Customer> batchCustomers = Arrays.asList(new Customer(), new Customer());
    //批量保存,saveAll是循環(huán)單挑插入，并不是batch操作，數(shù)據(jù)較大使用時(shí)請(qǐng)注意性能
//    List<Customer> batchSaves = customerRepository.saveAll(batchCustomers);
  }

delete操作

• delte操作會(huì)先執(zhí)行查詢(除了batch操作)，在執(zhí)行刪除，若查詢不到結(jié)果，拋出異常(EmptyResultDataAccessException)不執(zhí)行刪除

  /**
   * 刪除操作，除了batch操作，其他方法均先查詢后刪除
   */
  @Test
  public void delete() {
    //select * from customer where id=?;delete from customer where id=?;
    //同delete(entity)
    customerRepository.deleteById(38L);
    //select * from customer;循環(huán)遍歷id單個(gè)刪除...delete from customer where id=?...
    customerRepository.deleteAll();
    Customer customer = new Customer();
    customer.setId(Long.valueOf(42L));
    Customer customerOther = new Customer();
    customerOther.setId(41L);
    List<Customer> deleteAll = Arrays.asList(customer,customerOther);
    //循環(huán)執(zhí)行delete(entity)
    customerRepository.deleteAll(deleteAll);
    //不查詢直接：delete from customer;(風(fēng)險(xiǎn)較大清空表)
    customerRepository.deleteAllInBatch();
    //不查詢直接：delete from customer where id=? or id=?
    customerRepository.deleteInBatch(deleteAll);
  }

最常用的query操作

jpa 官方查詢關(guān)鍵字

單表字段查詢

    //select * from customer;
    customerRepository.findAll();
    //select * from customer where id = 1;
    customerRepository.findById(1L);
    //select * from customer where address = "address";
    customerRepository.findCustomerByAddress("address");
    //select * from customer where name = "lk" and phone = "133";
    customerRepository.findCustomersNameAndPhone("133", "lk");
    //select * from customer where name like '%k';
    customerRepository.findCustomersNameLike("k");
    //select * from customer where name like 'k'; 如果需要模糊查詢需要手動(dòng)拼接 % 連接符
    customerRepository.findCustomersByNameLike("k");
    //select * from customer where name like "%l";
    customerRepository.findCustomersByNameStartingWith("l");
    //select * from customer where name like "%k%";
    customerRepository.findCustomersByNameContains("k");
    / /.....還有很多，不再一一列舉......

分頁(yè)，排序

    //select * from customer order by name desc;
    customerRepository.findAll(Sort.by(Direction.DESC, "name"));
    //select * from customer limit 0,10;
    customerRepository.findAll(PageRequest.of(0, 10));

example查詢（場(chǎng)景較少）

    Customer customer = new Customer();
    customer.setAddress("address");
    //select * from customer where address ="address";
    customerRepository.findAll(Example.of(customer));
    customer.setName("lk");
    customer.setPhone("133");
    ExampleMatcher matcher = ExampleMatcher.matching()
        .withMatcher("name", match -> match.contains())
        .withMatcher("phone", match -> match.startsWith());
    //select * from customer where name like '%lk%" and phone like '133%' and address = "address";
    customerRepository.findOne(Example.of(customer, matcher));

namedQuery 也是自定義的@Query的一種

//entity
@Entity(name = "Customer")
@NamedQuery(name = "Customer.findByNameNQ", query = "select c from Customer c where name =?1")
public class Customer {}

//repository定義方法findByNameNQ
List<Customer> findByNameNQ(String name);

//test
//namedQuery:select * from customer where name = "lk";
customerRepository.findByNameNQ("lk");

@Query自定義JQL語(yǔ)句查詢，語(yǔ)法跟sql類似，但注意基于entity的命名，如果屬性nativeQuery為ture則，必須用原生sql語(yǔ)句

  @Query("select c from Customer c where name like %?1")
  List<Customer> findCustomersNameLike(String name);

  @Query("select c from Customer c where name = :name and phone = :phone")
  List<Customer> findCustomersNameAndPhone(@Param("phone") String phone,
      @Param("name") String name);

  @Query(value = "select * from customer where name =?1",nativeQuery = true)
  List<Customer> findByNameSql(String name);

@Modify 配合 @Query實(shí)現(xiàn) 修改部分字段

  @Modifying
  @Query("update Customer c set c.name = :name where c.id = :id")
  int modifyByPhone(@Param("name") String name,@Param("id") Long id);

  @Modifying
  @Query("delete from Customer c  where c.id = ?1")
  int deleteCustomer(Long id);

自定義返回值，基于JQL語(yǔ)法，在拼裝返回結(jié)果集時(shí)，是根據(jù)構(gòu)造函數(shù)進(jìn)行組裝的，可以基于接口或者類，要保證屬性是entity內(nèi)的屬性。也可以借助@Query，使用 new map()返回map，或者new Class返回想要的結(jié)果。

  //repository

  List<NameOnlyI> findCustomersByName(String name);

  List<NameOnly> findByName(String name);

  @Query("select new com.spring.jpa.beans.NameOnly(name,address) from Customer where name = ?1")
  List<NameOnly> findByName4Obj(String name);

  @Query("select new map(name as myname,address as myaddress) from Customer where name = :name")
  List<Map<String, Object>> findByName4Map(@Param("name") String name);

//test

    //基于接口的返回值
    List<NameOnlyI> interfaces = customerRepository.findCustomersByName("lk1");
    //基于類的返回值，如果有兩個(gè)構(gòu)造函數(shù)會(huì)報(bào)錯(cuò)，無(wú)法解析轉(zhuǎn)換
    List<NameOnly> nameOnlies = customerRepository.findByName("lk1");
    //基于類的返回值，@Query顯式聲明返回bean
    List<NameOnly> objs = customerRepository.findByName4Obj("lk1");
    //@Query返回map 用as做key，不用as默認(rèn)key是0，1，2...
    List<Map<String, Object>> maps = customerRepository.findByName4Map("lk1");

復(fù)雜關(guān)聯(lián)關(guān)系查詢 @OneToOne @ManyToMany @ManyToOne @OneToMany

customer 顧客表，和customer_group 多對(duì)一
customer_group 顧客分組表
book 書(shū)籍表，customer是多對(duì)多。
book_detail 書(shū)籍詳細(xì)表，和book是一對(duì)一

• 四張表沒(méi)任何業(yè)務(wù)，假象出來(lái)的，單純?yōu)榱蓑?yàn)證jpa查詢方式

表關(guān)系注解參數(shù)（@OneToOne @ManyToMany @ManyToOne @OneToMany ）

• Fetch
  抓取是否延遲加載，默認(rèn)情況一的方為立即加載，多的一方為延遲加載，可以手動(dòng)指定Fetch.EAGER/Fetch.LAZY
• mappedBy
  關(guān)聯(lián)關(guān)系由此方屬性維護(hù)，可以理解成一對(duì)注解使用mappedBy的一方由另一方維護(hù)，且必須是注解作用下的屬性名。

可以根據(jù)關(guān)聯(lián)表的屬性作為條件查詢，結(jié)果同樣是根據(jù)兩次sql查詢出來(lái)的。通過(guò)關(guān)聯(lián)表的屬性進(jìn)行查詢時(shí)，使用關(guān)聯(lián) entityName_columnName方式，或者直接使用 _columnName進(jìn)行查詢。如果不想級(jí)聯(lián)查詢時(shí)，在一方不適用注解即可。

@OneToOne

一對(duì)一關(guān)聯(lián)關(guān)系，有三種形式存在：

• 兩張表共享主鍵pk，使用@PrimaryKeyJoinColumn來(lái)建立關(guān)聯(lián)關(guān)系

@Entity
public class A {
  @Id
  private Long id;
  @OneToOne(cascade = CascadeType.ALL)
  @PrimaryKeyJoinColumn
  private B b;
}

@Entity
public class B {
  @Id
  private Long id;
}

• 通過(guò)中間表建立關(guān)聯(lián)關(guān)系，使用@JoinTable注解，joinColumns指定本表和關(guān)聯(lián)表的外鍵，inverseJoinColumns指定關(guān)聯(lián)關(guān)系另一方和關(guān)聯(lián)表的外鍵

@Entity
public class A {
  @Id
  private Long id;
  @OneToOne(cascade = CascadeType.ALL)
  joinColumns = @JoinColumn(name="a_fk"),
  inverseJoinColumns = @JoinColumn(name="b_fk")
  private B b;
}

@Entity
public class B {
  @Id
  private Long id;
  @OneToOne(mappedBy="b")
  private A a;
}

• 通過(guò)外鍵，唯一約束指定關(guān)聯(lián)關(guān)系，使用@JoinColumn注解，如果不寫該注解，默認(rèn)會(huì)在此表中自動(dòng)創(chuàng)建連接列：主表屬性_關(guān)聯(lián)表主鍵名稱

@Entity(name = "book")
public class Book {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  private String name;
  private Integer count;

  @OneToOne(cascade = CascadeType.ALL)
  @JoinColumn(name = "detail_id",referencedColumnName = "id")
//referencedColumnName 不寫默認(rèn)是主鍵，當(dāng)不是主鍵是可以用此聲明，但必須保證連接鍵在連接表是唯一約束的
  private BookDetail bookDetail;

//setter getter
}

@Entity(name = "book_detail")
public class BookDetail {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String size;
//不需要依賴book可以不寫關(guān)聯(lián)屬性

//setter getter
}

public interface BookRepository extends JpaRepository<Book, Long> {

  //可以查出關(guān)聯(lián)表的實(shí)體，結(jié)果是根據(jù)兩次sql查詢出來(lái)的，即select * from book where name = ?;->查出detail_id->select * from book_detail where id = ?;
  List<Book> findByName(String name);
  //可以根據(jù)關(guān)聯(lián)表的屬性作為條件查詢，結(jié)果同樣是根據(jù)兩次sql查詢出來(lái)的。通過(guò)關(guān)聯(lián)表的屬性進(jìn)行查詢時(shí)，使用關(guān)聯(lián) entityName_columnName方式，或者直接使用 _columnName進(jìn)行查詢。
  List<Book> findByNameAndBookDetail_Id(String name, Long id);

  //自定義返回值，一次查詢返回結(jié)果
  @Query("select new com.spring.jpa.beans.BookResult(b.id as id,b.name as name ,d.size as size) from Book as b left join BookDetail as d on b.bookDetail = d.id")
  List<BookResult> findResults();

}

@ManyToMany

• 通過(guò)@ManyToMany 注解定義多對(duì)多關(guān)系，同時(shí)通過(guò) @JoinTable 注解描述關(guān)聯(lián)表和關(guān)聯(lián)條件。

// 維護(hù)端注解
@Entity
public class A {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  @ManyToMany (cascade = CascadeType.REFRESH)
  @JoinTable (
           name =  "a_b" , //關(guān)聯(lián)表名
           inverseJoinColumns =  @JoinColumn (name =  "a_id" ),//被維護(hù)端外鍵
           joinColumns =  @JoinColumn (name =  "b_id" ))//維護(hù)端外鍵被維護(hù)端注解
   private B b;

//setter getter
}

@Entity
public class B {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  @ManyToMany(cascade = CascadeType.REFRESH,
            mappedBy = "b",//通過(guò)維護(hù)端的屬性關(guān)聯(lián)
            fetch = FetchType.LAZY)
// 關(guān)系維護(hù)端刪除時(shí)，如果中間表存在些紀(jì)錄的關(guān)聯(lián)信息，則會(huì)刪除該關(guān)聯(lián)信息;
// 關(guān)系被維護(hù)端刪除時(shí)，如果中間表存在些紀(jì)錄的關(guān)聯(lián)信息，則會(huì)刪除失敗 .
  private A a;

//setter getter
}

• 默認(rèn)joinColumn值：關(guān)聯(lián)表名：主表表名 + 下劃線 + 從表表名；關(guān)聯(lián)表到主表的外鍵：主表表名 + 下劃線 + 主表中主鍵列名；關(guān)聯(lián)表到從表的外鍵名：主表中用于關(guān)聯(lián)的屬性名+ 下劃線 + 從表的主鍵列名

@ManyToOne @OneToMany

• 注解和上面都差不多，無(wú)非就是誰(shuí)關(guān)聯(lián)誰(shuí)

@Entity
@NamedQuery(name = "Customer.findByNameNQ", query = "select c from Customer c where name =?1")
public class Customer {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  private String name;
  private String email;
  private String address;
  private String phone;

//  //targetEntity 默認(rèn)是關(guān)聯(lián)實(shí)體，若使用接口作為關(guān)聯(lián)實(shí)體時(shí)，應(yīng)指明targetEntity的實(shí)現(xiàn)類，且接口應(yīng)繼承Serializable，否則無(wú)法被解析
//  @ManyToOne(fetch = FetchType.EAGER,targetEntity = CustomerGroup.class)
//  @JoinColumn(name = "group_type",referencedColumnName = "type")
//  private CustomerGroupInterface customerGroup;

  //manyToOne 單向關(guān)聯(lián)或 oneToMany雙向關(guān)聯(lián)
//  //這里使用非主鍵作為外鍵關(guān)聯(lián)，type在customer_group表中唯一約束，也可以使用@JoinTable 處理關(guān)聯(lián)表做連接這里不再演示
  @ManyToOne(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
  @JoinColumn(name = "group_type",referencedColumnName = "type")
  private CustomerGroup customerGroup;

  //customerGroup為一的一方，單向關(guān)聯(lián)customer（多方）
//  @Column(name = "group_type")
//  private String type;

//setter getter
}

@Entity
@Table(name = "customer_group")
public class CustomerGroup implements CustomerGroupInterface {

  private static final long serialVersionUID = -6956725658881048590L;
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  @Column(unique = true)
  private String type;
  private String name;
  private Integer level;

  //oneToMany 單向關(guān)聯(lián)，customer中無(wú)需注解，注意joinColumn是table中的name
//  @OneToMany(fetch = FetchType.EAGER)
//  @JoinColumn(name = "group_type")

  //oneToMany 雙向關(guān)聯(lián)，customer中無(wú)需注解,mappedBy必須指向entity中的屬性名，即標(biāo)有@ManyToOne的屬性名，且此處不可再使用@JoinColumn。
  @OneToMany(fetch = FetchType.EAGER, mappedBy = "customerGroup")
  private List<Customer> customers;

//setter getter
}

其他注解

最后寫的比較急躁，代碼放github和碼云了：spring-data/github spring-data/碼云