Spring Data JPA實現數據庫訪問

1.創建子模塊

右鍵點擊工程名[mapcloudservice] --> New --> Module --> 選擇Maven -->設置子模塊的名稱[datamanager] --> Finish
創建成功後如下圖所示：

2.配置pom.xml

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

查看該項目的依賴關係圖：
方法一：右鍵點擊pom.xml文件中的任意處 --> Diagrams --> Show Dependencies
方法二：打開Maven工具欄，選擇 Show Dependencies

3.配置數據源

3.1 配置application.yml

首先在目錄/src/main/resources下創建application.yml，配置內容示例如下：

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/db_example?serverTimezone=UTC&useSSL=true&autoReconnect=true&failOverReadOnly=false
    username: chaoshui
    password: 123456
  jpa:
    database: mysql
    show-sql: true
    hibernate:
      ddl-auto: update
      naming:
        physical-strategy: org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
    open-in-view: false

3.2 注意事項

命名策略physical-strategy使用：org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl，Hibernate 會默認以實體名和屬性名分別作爲表名及字段名進行映射，但是如果添加了註解@Table和@Column，則以註解屬性值進行映射命名。

4.創建Entity類

entity用於關聯映射數據庫中的一張表，entity類需要完成以下幾項工作：
(1)註解
@Entity：表明這是一個實體類，與指定的數據庫表進行映射
@Id：該屬性映射爲數據庫的主鍵
@GeneratedValue：默認使用主鍵生成方式爲自增，hibernate會自動生成一個名爲HIBERNATE_SEQUENCE的序列
@Table：指定映射的表名，若沒有則根據類的名稱進行映射
@Column：指定映射的字段名
@OneToOne/@OneToMany/ManyToOne：一對一、一對多、多對一的關聯

(2)定義屬性，類型爲私有
(3)創建所有屬性所對應的setter和getter方法
(4)創建帶參數的構造器和無參數的構造函數
(5)重寫父類中的eauals()方法和hashcode()方法
(6)實現序列化並賦予其一個版本號。
示例代碼：

package com.emapgo.datamanager.entity;

import net.bytebuddy.implementation.HashCodeMethod;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cglib.core.HashCodeCustomizer;
import sun.security.util.AuthResources_pt_BR;

import javax.persistence.*;
import java.io.Serializable;

@Entity
@Table(name = "UserManage")
public class UserManage implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "clientID")
    private String clientID;

    @Column(name = "username")
    private String username;
    @Column(name = "password")
    private String password;
    @Column(name = "credentials")
    private String credentials;
    @Column(name = "grantType")
    private String grantType;
    @Column(name = "accessToken")
    private String accessToken;
    @Column(name = "tokenType")
    private String tokenType;
    @Column(name = "expireIN")
    private String expireIN;
    @Column(name = "scope")
    private String scope;

    public UserManage(){}

    public UserManage(String _clientID,
                      String _username,
                      String _password,
                      String _credentials,
                      String _grantType,
                      String _accessToken,
                      String _tokenType,
                      String _expireIN,
                      String _scope){
        this.clientID = _clientID;
        this.username = _username;
        this.password = _password;
        this.credentials = _credentials;
        this.grantType = _grantType;
        this.accessToken = _accessToken;
        this.tokenType = _tokenType;
        this.expireIN = _expireIN;
        this.scope = _scope;
    }

    // getter and setter methods
    public String getClientID() {
        return clientID;
    }
    public String getUsername() {
        return username;
    }
    public String getPassword() {
        return password;
    }
    public String getCredentials() {
        return credentials;
    }
    public String getGrantType() {
        return grantType;
    }
    public String getAccessToken() {
        return accessToken;
    }
    public String getTokenType() {
        return tokenType;
    }
    public String getExpireIN() {
        return expireIN;
    }
    public String getScope() {
        return scope;
    }
    public void setClientID(String clientID) {
        this.clientID = clientID;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public void setCredentials(String credentials) {
        this.credentials = credentials;
    }
    public void setGrantType(String grantType) {
        this.grantType = grantType;
    }
    public void setAccessToken(String accessToken) {
        this.accessToken = accessToken;
    }
    public void setTokenType(String tokenType) {
        this.tokenType = tokenType;
    }
    public void setExpireIN(String expireIN) {
        this.expireIN = expireIN;
    }
    public void setScope(String scope) {
        this.scope = scope;
    }
    
    @Override
    public String toString(){
        return  "Table-UserManage: " + "(" + this.clientID + "," + this.username + "," +
                this.password + "," + this.credentials + "," +
                this.grantType + "," + this.accessToken + "," +
                this.expireIN + "," + this.scope + ")\n";
    }

    // @Override
    // public int hashCode(){}

    // @Override
    // public boolean equals(Object obj){
    //     if(this == obj){
    //         return true;
    //     }
    //     if(obj == null || (getClass() != obj.getClass())){
    //         return false;
    //     }

    //     UserManage other = (UserManage) obj;
    //     if(!this.clientID.equals(other.clientID)){
    //         return false;
    //     }
    //     return true;
    // }
}

5.創建Repository接口

5.1創建repository接口

目的是通過repository訪問MySQL數據庫。

(1) 需要添加entity的類型和ID的類型用於表示關聯哪個entity。
(2) 增刪改查等操作方法只需按照書寫規範進行聲明，不需要實現，spring data jpa會在運行程序時根據方法名稱自動創建相關的實現，如下圖所示是CrudRepository接口中的全部方法

@NoRepositoryBean
public interface CrudRepository<T, ID> extends Repository<T, ID> {
	// 保存指定的entity
    <S extends T> S save(S var1);
	// 保存所有的entity
    <S extends T> Iterable<S> saveAll(Iterable<S> var1);
	// 根據指定屬性返回entity
    Optional<T> findById(ID var1);
	// 判斷具有指定屬性的entity是否存在
    boolean existsById(ID var1);
	// 返回全部entity
    Iterable<T> findAll();
	// 根據指定屬性返回全部entity
    Iterable<T> findAllById(Iterable<ID> var1);
	// 返回entity的數量
    long count();
	// 根據指定的屬性刪除entity
    void deleteById(ID var1);
	// 刪除指定的entity
    void delete(T var1);
	// 刪除全部entity
	void deleteAll();
   
	void deleteAll(Iterable<? extends T> var1);   
}

(3) 方法名支持的Query關鍵字：

Keyword	Sample	JPQL snippet
And	findByLastnameAndFirstname	… where x.lastname = ?1 and x.firstname = ?2
Or	findByLastnameOrFirstname	… where x.lastname = ?1 or x.firstname = ?2
Is, Equals	findByFirstname,findByFirstnameIs,findByFirstnameEquals	… where x.firstname = ?1
Between	findByStartDateBetween	… where x.startDate between ?1 and ?2
LessThan	findByAgeLessThan	… where x.age < ?1
LessThanEqual	findByAgeLessThanEqual	… where x.age <= ?1
GreaterThan	findByAgeGreaterThan	… where x.age > ?1
GreaterThanEqual	findByAgeGreaterThanEqual	… where x.age >= ?1
After	findByStartDateAfter	… where x.startDate > ?1
Before	findByStartDateBefore	… where x.startDate < ?1
IsNull, Null	findByAge(Is)Null	… where x.age is null
IsNotNull, NotNull	findByAge(Is)NotNull	… where x.age not null
Like	findByFirstnameLike	… where x.firstname like ?1
NotLike	findByFirstnameNotLike	… where x.firstname not like ?1
StartingWith	findByFirstnameStartingWith	… where x.firstname like ?1 (parameter bound with appended %)
EndingWith	findByFirstnameEndingWith	… where x.firstname like ?1 (parameter bound with prepended %)
Containing	findByFirstnameContaining	… where x.firstname like ?1 (parameter bound wrapped in %)
OrderBy	findByAgeOrderByLastnameDesc	… where x.age = ?1 order by x.lastname desc
Not	findByLastnameNot	… where x.lastname <> ?1
In	findByAgeIn(Collection ages)	… where x.age in ?1
NotIn	findByAgeNotIn(Collection ages)	… where x.age not in ?1
True	findByActiveTrue()	… where x.active = true
False	findByActiveFalse()	… where x.active = false
IgnoreCase	findByFirstnameIgnoreCase	… where UPPER(x.firstame) = UPPER(?1)

(4) 可以繼承的接口有四個：

Repository
CrudRepository
PagingAndSortingRepository
QueryByExampleExecutor

接口間繼承關係如下：

5.2基於Query註解的CRUD

在繼承JpaRepository接口的方法中，可以在自定義的查詢方法上使用@Query，來指定該方法要執行的自定義的查詢語句。其中的value值可以是任意的查詢語句，同樣只需要進行方法的定義，無需進行實現。

5.3示例代碼

package com.emapgo.datamanager.repository;

import com.emapgo.datamanager.entity.UserManage;
import org.springframework.data.repository.CrudRepository;
import java.util.List;

public interface UserManageRepository extends CrudRepository<UserManage, String>
{
    // find
    List<UserManage> findAllByClientID(String clientID);
    List<UserManage> findAllByUsername(String username);
    List<UserManage> findAllByPassword(String password);
    List<UserManage> findAllByCredentials(String credentials);
    List<UserManage> findAllByGrantType(String grantType);
    List<UserManage> findAllByAccessToken(String accessToken);
    List<UserManage> findAllByTokenType(String tokenType);
    List<UserManage> findAllByExpireIN(String expireIN);
    List<UserManage> findAllByScope(String scope);

    UserManage findByClientID(String clientID);
    UserManage findByUsername(String username);
    UserManage findByPassword(String password);
    UserManage findByCredentials(String credentials);
    UserManage findByGrantType(String grantType);
    UserManage findByAccessToken(String accessToken);
    UserManage findByTokenType(String tokenType);
    UserManage findByExpireIN(String expireIN);
    UserManage findByScope(String scope);

    UserManage findByClientIDAndAccessToken(String cleintID, String accessToken);
    // ...等等

    // save
    // 略

    // update
    @Modifying
    @Transactional
    @Query(value = "update UserManage um set um.username = ?1 where um.clientID = ?2", nativeQuery = true)
    public void UpdateUsernameByClientID(String username, String clientID);
    //  ...等等

    // delete
    @Modifying
    @Transactional
    int deleteByClientID(String clientID);
    //  ...等等
}

5.3選擇性暴露部分CRUD方法

示例如下

@NoRepositoryBean
interface BaseRepository<T, ID> extends Repository<T, ID> {
	Optional<T> findById(ID id);
	<S extends T> S save(S entity);
}
interface UserManageRepository extends BaseRepository<User, Long> {
	// 略
}

6.創建Controller

略

7.添加主程序，測試

@SpringBootApplication
public class datamanageapplication {
    @Autowired
    UserManageRepository umr;

    public static void main(String[] args) {
        SpringApplication.run(datamanageapplication.class, args);
    }
    @Bean
    public CommandLineRunner userManageDemo(){
        System.out.println("-----------------------> **hello world** <-------------------------");

        return (args) -> {
            // insert
            umr.save(new UserManage("client_00", "lingwen_00", "123456_00", "creden_00", "grant_00","access_00", "token_00", "expire_00", "scope_00"));
            umr.save(new UserManage("client_01", "lingwen_01", "123456_01", "creden_01", "grant_01","access_01", "token_01", "expire_01", "scope_01"));


            // update
            umr.UpdateUsernameByClientID("lingwen_01", "client_00");
            System.out.println("Updated OK!");

            // fetch all records
            System.out.println("usermanager found with findAll(): ");
            System.out.println("----------------------------------");
            for(UserManage um : umr.findAll()){
                System.out.println(um.toString());
            }
            System.out.println();

            // fetch all records by clientID
            List<UserManage> um1 = umr.findAllByClientID("client_00");
            System.out.println("user manage found with findById(1L):");
            System.out.println("-----------------------------");
            System.out.println(um1.toString());

            // fetch all records by grant_type
            UserManage um2 = umr.findByScope("scope_00");
            System.out.println("user manage found with findById(2L):");
            System.out.println("-----------------------------");
            if(um2 != null){
                System.out.println(um2.toString());
            }else {
                System.out.println("cannot find any record that have attribute 'scope_00' in table UserManage!");
            }
            System.out.println();

            // fetch all user manage by ******
            // 略

            // delete
            umr.deleteByClientID("client_08");
            System.out.println("deleted OK!");

        };

   }


}

8.可能遇到的問題

寫entity類的時候，相關注解會出現紅色波浪線，並且在最終運行程序的時候會失敗(但是底層Hibernate顯示可以連接上數據庫)，如下圖所示

解決方法：

點擊View --> ToolWindows -> Persistence，在左下區域出現Persistence
右鍵點擊Entity --> Generate Persistence Mapping --> By Database Schema，在彈出的對話框中選擇Choose Data Source
配置好數據庫相關的選項，可以點擊Test Connection測試能否連接成功
完了之後點擊OK，回到上一個對話框，點擊Database Schema mapping下的刷新，選中UserManage表 --> OK (必須點刷新，不點刷新不會自動出現這些內容)
右鍵單擊Entity --> Assign Datasource 配置數據源

配置完以後，紅色波浪線消失，程序能夠正常運行，增刪改查等操作執行也沒有問題
原因分析：暫時不清楚

參考資料

1.Spring Data JPA - Reference Documentation
2.Accessing Data with Spring Data JPA and MySQL
3.Getting Started with Spring Data JPA
4.spring data jpa 實戰之增刪改查（乾貨！你想要的查詢！）
5.Spring Data JPARepository Example
其他相關參考資料：
Create your first Java application
Spring MVC框架入門教程
 MySQL Java tutorial

Spring Data JPA實現數據庫訪問

1.創建子模塊

2.配置pom.xml

3.配置數據源

3.1 配置application.yml

3.2 注意事項

4.創建Entity類

5.創建Repository接口

5.1創建repository接口

5.2基於Query註解的CRUD

5.3示例代碼

5.3選擇性暴露部分CRUD方法

6.創建Controller

7.添加主程序，測試

8.可能遇到的問題

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