春季数据 JDBC – 一对多示例

电玩女神 2023-09-25 12:19 36阅读 0赞

一个基本的快速**春季数据JDBC**示例，介绍如何映射实体中的**一对****多**数据库表关系。

### 1. 数据库表 ###

让我们看一下下表，我们可以说**分支**和**学生**之间的关系是**一对多**的。每个学院工程分部都有多个学生人数。

CREATE TABLE `BRANCH` (
      `BRANCH_ID` int(11) NOT NULL AUTO_INCREMENT,
      `BRANCH_SHORT_NAME` varchar(45) NOT NULL,
      `BRANCH_NAME` varchar(100) NOT NULL,
      `DESCRIPTION` varchar(200) DEFAULT NULL,
      PRIMARY KEY (`BRANCH_ID`)
    );
    
    
    CREATE TABLE `STUDENT` (
      `ID` int(11) NOT NULL AUTO_INCREMENT,
      `FIRST_NAME` varchar(45) DEFAULT NULL,
      `LAST_NAME` varchar(45) DEFAULT NULL,
      `CONTACT_NO` varchar(45) DEFAULT NULL,
      `BRANCH_ID` int(11) DEFAULT NULL,
      PRIMARY KEY (`ID`),
      CONSTRAINT `BRANCH_ID_FK` 
        FOREIGN KEY (`BRANCH_ID`) 
        REFERENCES `BRANCH` (`BRANCH_ID`)
    );

### 2. 项目配置 ###

1.1. **使用的技术** ：

1.  Spring Boot 2.3.0.RELEASE
2.  Spring Data JDBC 2.0.0.RELEASE
3.  Spring Framework 5.2.6.RELEASE
4.  H2 / MySql DB
5.  Lombok 1.18.12
6.  JUnit 5

1.2. **Maven 依赖关系** ：

要开始使用弹簧启动与**弹簧数据JDBC，**您需要依赖项`spring-boot-starter-data-jdbc`。使用[龙目岛][Link 1]来避免样板代码。下面是示例应用程序中使用的完整依赖项列表。

<dependencies>
    		<dependency>
    			<groupId>org.springframework.boot</groupId>
    			<artifactId>spring-boot-starter-data-jdbc</artifactId>
    		</dependency>
    		<dependency>
    			<groupId>org.springframework.boot</groupId>
    			<artifactId>spring-boot-starter-web</artifactId>
    		</dependency>
    		<dependency>
    			<groupId>org.springframework.boot</groupId>
    			<artifactId>spring-boot-starter-validation</artifactId>
    		</dependency>
    		<dependency>
    			<groupId>com.h2database</groupId>
    			<artifactId>h2</artifactId>
    		</dependency>
    		<dependency>
    			<groupId>org.projectlombok</groupId>
    			<artifactId>lombok</artifactId>
    		</dependency>
    		<dependency>
    			<groupId>mysql</groupId>
    			<artifactId>mysql-connector-java</artifactId>
    			<scope>runtime</scope>
    		</dependency>
    		<dependency>
    			<groupId>org.springframework.boot</groupId>
    			<artifactId>spring-boot-starter-test</artifactId>
    			<scope>test</scope>
    		</dependency>
    	</dependencies>

### 3. 实体映射 ###

3.1. **学生实体** ：

@Data // lombok
    public class Student {
    
    	@Id
    	private Long id;
    
    	private String contactNo;
    	private String firstName;
    	private String lastName;
    
    }

3.2. **分支实体** ：

要在实体中映射一对多关系，我们必须在**集合**上使用**@MappedCollection**，如**列表**或**集**或**映射**。

@Data
    public class Branch {
    
    	@Id
    	private int branchId;
    
    	private String branchName;
    	private String branchShortName;
    	private String description;
    
    	@MappedCollection(keyColumn = "BRANCH_ID", idColumn = "BRANCH_ID")
    	private Set<Student> students;
    
    }

### 4. 测试映射 ###

4.1. 为**分支**实体创建一个 JDBC 存储库来执行基本的数据库操作。

@Repository
    public interface BranchOneToManyTestRepository extends CrudRepository<Branch, Long>{
    
    }

4.2. **测试用例**

@SpringBootTest
    public class OneToManyMappingTest extends BaseTest {
    
    	@Autowired
    	private BranchOneToManyTestRepository testRepository;
    
    	@Test
    	@DisplayName("One-to-Many Mapping Test")
    	@Sql(scripts = "/one-to-many-mapping.sql")
    	void embeddedMappingTest() {
    
    		Branch branch = new Branch();
    		branch.setBranchShortName("CSE");
    		branch.setBranchName("Computer Science and Engineering");
    		branch.setDescription("CSE department offers courses under ambitious curriculam in computer science and computer engineering..");
    		Set<Student> students = new HashSet<>();
    		students.add(getStudent1());
    		students.add(getStudent2());
    		branch.setStudents(students);
    
    		Branch createdBranch = testRepository.save(branch);
    		System.err.println(createdBranch);
    		Assert.assertTrue(createdBranch != null);
    	}
    
    	private static Student getStudent1() {
    		Student student = new Student();
    		student.setFirstName("Rosy");
    		student.setLastName("Larsen");
    		student.setContactNo("+1-408-575-1317");
    
    		return student;
    	}
    
    	private static Student getStudent2() {
    		Student student = new Student();
    		student.setFirstName("Rosy");
    		student.setLastName("Larsen");
    		student.setContactNo("+1-408-575-1219");
    
    		return student;
    	}
    }

### 5. 结论 ###

在本教程中，我们介绍了如何在春季数据JDBC中映射一对多关联。

在 [Git 中心][Git]查看源代码。

**其他春季数据 JDBC 示例** ：

1.  [春季数据 JDBC – 嵌入式实体][JDBC _]
2.  [春季数据 JDBC – 分页][JDBC _ 1]
3.  [春季数据JDBC - 多对多][JDBC -]
4.  [春季数据JDBC – 一对一][JDBC _ 2]
5.  [春季数据 JDBC – 查询派生][JDBC _ 3]
6.  [弹簧启动 – 加载初始数据][Link 2]

### 6. 参考资料 ###

1.  [春季文档][Link 3]
2.  [龙目岛@Data][Data]
3.  [休眠一对多单向][Link 4]
4.  [弹簧启动数据 JDBC 示例][JDBC]
5.  [弹簧启动 H2 内存数据库][H2]

[Link 1]: https://javabydeveloper.com/project-lombok-tutorial/
[Git]: https://github.com/javabydeveloper/spring-boot/tree/master/spring-boot-data-jdbc-example/src/test/java/com/javabydeveloper/demo
[JDBC _]: https://javabydeveloper.com/spring-data-jdbc-embedded-entities-examples/
[JDBC _ 1]: https://javabydeveloper.com/spring-data-jdbc-pagination-and-sorting-example/
[JDBC -]: https://javabydeveloper.com/spring-data-jdbc-many-to-many-example/
[JDBC _ 2]: https://javabydeveloper.com/spring-data-jdbc-one-to-one-example/
[JDBC _ 3]: https://javabydeveloper.com/spring-data-jdbc-query-derivation-examples/
[Link 2]: https://javabydeveloper.com/spring-boot-loading-initial-data/
[Link 3]: https://docs.spring.io/spring-data/jdbc/docs/current/reference/html/#jdbc.entity-persistence.custom-column-name
[Data]: https://javabydeveloper.com/lombok-data-annotation/
[Link 4]: https://javabydeveloper.com/one-many-unidirectional-association/
[JDBC]: https://javabydeveloper.com/spring-data-jdbc-2-0-with-spring-boot-example/
[H2]: https://javabydeveloper.com/spring-boot-h2-in-memory-database-example/