为Mybatis创建Gradle项目
使用idea创建gradle项目
项目结构：
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
|
├── build.gradle
├── gradle
│ └── wrapper
│ ├── gradle-wrapper.jar
│ └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
├── settings.gradle
└── src
├── main
│ ├── java
│ └── resources
└── test
├── java
└── resources
9 directories, 6 files
|
编写build.gradle
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
|
plugins {
id 'java'
}
group 'io.github.qinry'
version '1.0-SNAPSHOT'
jar {
archivesBaseName = 'mybatis-sample'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'org.mybatis:mybatis:3.5.7'
runtimeOnly 'mysql:mysql-connector-java:8.0.27'
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'
}
test {
useJUnitPlatform()
}
|
添加依赖org.mybatis:mybatis:3.5.7和mysql:mysql-connector-java:8.0.27，mybatis编译和运行都使用，作用域设置为implement，mysql-connector-java在运行时有效设置为runtimeOnly。设置打包的jar的文档基名为mybatis-sample。
编写settings.gradle
1
|
rootProject.name = 'mybatis-sample'
|
根项目名为 mybatis-sample，如果有子项目，要使用include后跟子项目的名称，把子项目声明在这里让gradle知道。
Mybatis配置
编写mybatis的xml配置
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
|
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="/db.properties">
</properties>
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false" />
</settings>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="io/github/qinry/mapper/StudentMapper.xml" />
<mapper resource="io/github/qinry/mapper/GradeMapper.xml" />
</mappers>
</configuration>
|
# src/main/resources/db.properties
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC&useUnicode=true&characterEncoding=UTF-8
username=springuser
password=123456
配置最重要的两项，分别是environment和mappers。environment里最重要的是配置transactionManger和dataSource。
transactionManager事务管理器一般用JDBC。dataSource数据源的类型是Mybatis的POOLED，设置数据源的url、username、password还有driver。mappers配置的xml映射文件的位置。
创建数据库表
在mysql建库testdb还有创建两张表。
1
2
3
4
5
6
|
create table student(
id bigint not null auto_increment,
stu_name varchar(32) default null,
grade_id bigint default null,
primary key (id)
)engine=innodb default charset=utf8mb4;
|
1
2
3
4
5
|
create table grade(
id bigint not null auto_increment,
grade_name varchar(32) default null,
primary key (id)
)engine=innodb default charset=utf8mb4;
|
测试数据：
为grade表插入三条数据
1
2
3
4
|
insert into grade(grade_name) values
('一年级'),
('二年级'),
('三年级');
|
为student表插入三条数据
1
2
3
4
|
insert into student(stu_name, grade_id) values
('王二', 1),
('张三', 2),
('李四', 3);
|
创建实体pojo
创建Student类
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
|
package io.github.qinry.pojo;
public class Student implements Serializable {
private static final long serialVersionUID = 1L;
private Long id;
private String stuName;
private Long gradeId;
private Grade grade;
public Student() {
}
public Student(Long id, String stuName, Long gradeId) {
this.id = id;
this.stuName = stuName;
this.gradeId = gradeId;
}
public Student(String stuName, Long gradeId) {
this.stuName = stuName;
this.gradeId = gradeId;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getStuName() {
return stuName;
}
public void setStuName(String stuName) {
this.stuName = stuName;
}
public Long getGradeId() {
return gradeId;
}
public void setGradeId(Long gradeId) {
this.gradeId = gradeId;
}
public Grade getGrade() {
return grade;
}
public void setGrade(Grade grade) {
this.grade = grade;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", stuName='" + stuName + '\'' +
", gradeId=" + gradeId +
", grade=" + grade +
'}';
}
}
|
Student类属性为id、stuName、gradeId，还有关联属性grade。
创建Grade类
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
|
package io.github.qinry.pojo;
import java.util.List;
public class Grade implements Serializable {
private static final long serialVersionUID = 2L;
private Long id;
private String gradeName;
private List<Student> students;
public Grade() {
}
public Grade(String gradeName) {
this.gradeName = gradeName;
}
public Grade(Long id, String gradeName) {
this.id = id;
this.gradeName = gradeName;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getGradeName() {
return gradeName;
}
public void setGradeName(String gradeName) {
this.gradeName = gradeName;
}
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
@Override
public String toString() {
return "Grade{" +
"id=" + id +
", gradeName='" + gradeName + '\'' +
", students=" + students +
'}';
}
}
|
Grade类的属性id、gradeName，还有关联属性grades。
Student和Grade两表之间关系是一对多。
编写xml映射文件
改写mybatis-config.xml，在environments标签前添加typeAliases标签。
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
...
<typeAliases>
<package name="io.github.qinry.pojo"/>
</typeAliases>
<environments default="development">
...
</environments>
<mappers>
...
</mappers>
</configuration>
|
在编写xml映射文件时，使用pojo类型时可以直接使用类名（如Student），无须完全限定名（如io.github.qinry.pojo.Student）。
编写StudentMapper.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="io.github.qinry.mapper.StudentMapper">
<cache></cache>
<sql id="column_list">
id,stu_name,grade_id
</sql>
<select id="findAll" >
select
<include refid="column_list" />
from student
</select>
</mapper>
|
编写GradeMapper.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="io.github.qinry.mapper.GradeMapper">
<cache></cache>
<sql id="column_list">
id,grade_name
</sql>
<select id="findAll" resultType="Grade">
select
<include refid="column_list" />
from grade
</select>
</mapper>
|
update、insert、delete的编写类似，就不重复描述。
编写测试
测试StudentMapper
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
|
public class StudentMapperTests {
private SqlSessionFactory sqlSessionFactory;
@BeforeEach
void setUp() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis/mybatis-config.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
void findAll() throws IOException {
try (SqlSession session = sqlSessionFactory.openSession()) {
List<Student> students = session.selectList("io.github.qinry.mapper.StudentMapper.findAll");
students.forEach(System.out::println);
}
}
}
|
输出：
1
2
3
|
Student{id=1, stuName='王二', gradeId=1, grade=null}
Student{id=2, stuName='张三', gradeId=2, grade=null}
Student{id=3, stuName='李四', gradeId=3, grade=null}
|
测试GradeMapper
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
public class GradeMapperTests {
private SqlSessionFactory sqlSessionFactory;
@BeforeEach
void setUp() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis/mybatis-config.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
void findAll() throws IOException {
try (SqlSession session = sqlSessionFactory.openSession()) {
List<Grade> grades = session.selectList("io.github.qinry.mapper.GradeMapper.findAll");
grades.forEach(System.out::println);
}
}
}
|
输出：
1
2
3
|
Grade{id=1, gradeName='一年级', students=null}
Grade{id=2, gradeName='二年级', students=null}
Grade{id=3, gradeName='三年级', students=null}
|
添加映射器接口
接口名与xml映射文件命名空间一致，方法名与映射文件的与sql相关标签的id一致，比如select标签
添加接口StudentMapper
1
2
3
|
public interface StudentMapper {
List<Student> findAll();
}
|
添加接口与GradeMapper
1
2
3
|
public interface GradeMapper {
List<Grade> findAll();
}
|
修改mybatis-config.xml的mappers标签
1
2
3
|
<mappers>
<package name="io.github.qinry.mapper"/>
</mappers>
|
修改测试用例
1
2
3
4
5
6
7
|
@Test
void findAll() throws IOException {
try (SqlSession session = sqlSessionFactory.openSession()) {
StudentMapper mapper = session.getMapper(StudentMapper.class);
mapper.findAll().forEach(System.out::println);
}
}
|
1
2
3
4
5
6
7
|
@Test
void findAll() throws IOException {
try (SqlSession session = sqlSessionFactory.openSession()) {
GradeMapper mapper = session.getMapper(GradeMapper.class);
mapper.findAll().forEach(System.out::println);
}
}
|
得到输出结果与未修改一样，不这种方式（getMapper），使用SqlSession相对简洁。
编写高级结果集映射
修改StudentMapper.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
|
<resultMap id="studentResult" type="Student">
<id property="id" column="stu_id"/>
<result property="stuName" column="stu_name" />
<result property="gradeId" column="grade_id"></result>
<association property="grade" column="grade_id" resultMap="gradeResult"/>
</resultMap>
<resultMap id="gradeResult" type="Grade">
<id property="id" column="grade_id" />
<result property="gradeName" column="grade_name" />
</resultMap>
<select id="findAll" resultMap="studentResult">
select
s.id as stu_id,
s.stu_name as stu_name,
g.id as grade_id,
g.grade_name as grade_name
from student s
left outer join grade g on s.grade_id = g.id
</select>
|
测试用例输出：
1
2
3
|
Student{id=1, stuName='王二', gradeId=1, grade=Grade{id=1, gradeName='一年级', students=null}}
Student{id=2, stuName='张三', gradeId=2, grade=Grade{id=2, gradeName='二年级', students=null}}
Student{id=3, stuName='李四', gradeId=3, grade=Grade{id=3, gradeName='三年级', students=null}}
|
修改GradeMapper.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
|
<resultMap id="gradeResult" type="Grade">
<id property="id" column="grade_id" />
<result property="gradeName" column="grade_name" />
<collection property="students" ofType="Student" resultMap="studentResult" />
</resultMap>
<resultMap id="studentResult" type="Student">
<id property="id" column="stu_id" />
<result property="stuName" column="stu_name" />
</resultMap>
<select id="findAll" resultMap="gradeResult">
select
g.id as grade_id,
g.grade_name as grade_name,
s.id as stu_id,
s.stu_name as stu_name
from grade g
left outer join student s on g.id = s.grade_id
</select>
|
测试用例输出：
1
2
3
|
Grade{id=1, gradeName='一年级', students=[Student{id=1, stuName='王二', gradeId=null, grade=null}]}
Grade{id=2, gradeName='二年级', students=[Student{id=2, stuName='张三', gradeId=null, grade=null}]}
Grade{id=3, gradeName='三年级', students=[Student{id=3, stuName='李四', gradeId=null, grade=null}]}
|
高级结果集映射，使用级联查询（联表查询），实体必须实现Serializable接口。
了解更多