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Mybatis(三)
1 Mybaits--动态SQL
- 动态SQL是Mybatis强大特性之一。极大的简化我们拼装SQL的操作。
- 动态SQL元素和使用JSTL或其他类似基于XML的文本处理器相似。
- Mybatis采用功能强大的基于OGNL的表达式来简化操作。
- if
- choose(when ,otherwise)
- trim(where,set)
- foreach
1.1 动态SQL之if
package cn.demo2; /** * 描述:POJO */ public class Employee { private Integer id; private String lastName; private String gender; private String email; private Department department; public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } @Override public String toString() { return "Employee{" + "email=‘" + email + ‘\‘‘ + ", gender=‘" + gender + ‘\‘‘ + ", lastName=‘" + lastName + ‘\‘‘ + ", id=" + id + ‘}‘; } }
package cn.demo2; import java.util.List; public interface IEmployeeDAO { public List<Employee> getConditionIf(Employee employee); }
<?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="cn.demo2.IEmployeeDAO"> <select id="getConditionIf" resultType="cn.demo2.Employee" > SELECT id,last_name lastName,email,gender from employee WHERE <if test="id != null"> id = #{id} </if> <if test="lastName != null and lastName != ‘‘"> and last_name like #{lastName} </if> <if test="email != null and email.trim() != ‘‘"> and email = #{email} </if> <if test="gender == ‘男‘ or gender == ‘女‘"> and gender = #{gender} </if> </select> </mapper>
package cn.test; import cn.demo2.Employee; import cn.demo2.IEmployeeDAO; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.List; public class MybatisTest2 { /** * 测试查询 * @throws IOException */ @Test public void demo1() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); IEmployeeDAO dao = session.getMapper(IEmployeeDAO.class); Employee employee = new Employee(); employee.setId(5); List<Employee> employees = dao.getConditionIf(employee); System.out.print(employees); session.close(); } }
1.2 动态SQL之where
- 如果上面的程序中的id没有传入,那么拼接的SQL会多出and。
- 解决方案一:在where之后加上1=1。
- 解决方案二:Mybatis推荐使用where标签来将所有的查询条件包括在内,Mybatis就会将where标签中多出的and或or删除自动删除。并且where标签只会去掉第一个多出的and或or等。
package cn.demo2; /** * 描述:POJO */ public class Employee { private Integer id; private String lastName; private String gender; private String email; private Department department; public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } @Override public String toString() { return "Employee{" + "email=‘" + email + ‘\‘‘ + ", gender=‘" + gender + ‘\‘‘ + ", lastName=‘" + lastName + ‘\‘‘ + ", id=" + id + ‘}‘; } }
<?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="cn.demo2.IEmployeeDAO"> <select id="getConditionIf" resultType="cn.demo2.Employee" > SELECT id,last_name lastName,email,gender from employee <where> <if test="id != null"> id = #{id} </if> <if test="lastName != null and lastName != ‘‘"> and last_name like #{lastName} </if> <if test="email != null and email.trim() != ‘‘"> and email = #{email} </if> <if test="gender == ‘男‘ or gender == ‘女‘"> and gender = #{gender} </if> </where> </select> </mapper>
package cn.test; import cn.demo2.Employee; import cn.demo2.IEmployeeDAO; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.List; public class MybatisTest2 { /** * 测试查询 * @throws IOException */ @Test public void demo1() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); IEmployeeDAO dao = session.getMapper(IEmployeeDAO.class); Employee employee = new Employee(); employee.setLastName("%呵%"); List<Employee> employees = dao.getConditionIf(employee); System.out.print(employees); session.close(); } }
1.2 动态SQL之trim
package cn.demo2; /** * 描述:POJO */ public class Employee { private Integer id; private String lastName; private String gender; private String email; private Department department; public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } @Override public String toString() { return "Employee{" + "email=‘" + email + ‘\‘‘ + ", gender=‘" + gender + ‘\‘‘ + ", lastName=‘" + lastName + ‘\‘‘ + ", id=" + id + ‘}‘; } }
package cn.demo2; import java.util.List; public interface IEmployeeDAO { public List<Employee> getConditionIf(Employee employee); }
<?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="cn.demo2.IEmployeeDAO"> <select id="getConditionIf" resultType="cn.demo2.Employee" > SELECT id,last_name lastName,email,gender from employee <!-- where标签职能消除前面多余的and或者or之类的语句,而如果and或or在之后,那么where就无能为力了 trim可以来解决这样的问题 prefix表示在拼接的SQL之前加前缀 prefixOverrides是将前面多余的and或or等消除 suffix和prefix相反 prefixOverrides和prefixOverrides相反 --> <trim prefix="where" suffixOverrides="and"> <if test="id != null"> id = #{id} and </if> <if test="lastName != null and lastName != ‘‘"> last_name like #{lastName} and </if> <if test="email != null and email.trim() != ‘‘"> email = #{email} and </if> <if test="gender == ‘男‘ or gender == ‘女‘"> and gender = #{gender} </if> </trim> </select> </mapper>
package cn.test; import cn.demo2.Employee; import cn.demo2.IEmployeeDAO; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.List; public class MybatisTest2 { /** * 测试查询 * @throws IOException */ @Test public void demo1() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); IEmployeeDAO dao = session.getMapper(IEmployeeDAO.class); Employee employee = new Employee(); employee.setLastName("%呵%"); List<Employee> employees = dao.getConditionIf(employee); System.out.print(employees); session.close(); } }
1.3 动态SQL之分支查询(和Java中的switch--case相似)
package cn.demo2; /** * 描述:POJO */ public class Employee { private Integer id; private String lastName; private String gender; private String email; private Department department; public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } @Override public String toString() { return "Employee{" + "email=‘" + email + ‘\‘‘ + ", gender=‘" + gender + ‘\‘‘ + ", lastName=‘" + lastName + ‘\‘‘ + ", id=" + id + ‘}‘; } }
package cn.demo2; import java.util.List; public interface IEmployeeDAO { public List<Employee> getConditionIf(Employee employee); }
<?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="cn.demo2.IEmployeeDAO"> <select id="getConditionIf" resultType="cn.demo2.Employee" > SELECT id,last_name lastName,email,gender from employee <where> <choose> <when test="id != null"> id = #{id} </when> <when test="lastName != null"> last_name like #{lastName} </when> <when test="email != null"> email = #{email} </when> <otherwise> gender = #{gender} </otherwise> </choose> </where> </select> </mapper>
package cn.test; import cn.demo2.Employee; import cn.demo2.IEmployeeDAO; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import java.io.IOException; import java.io.InputStream; import java.util.List; public class MybatisTest2 { /** * 测试查询 * @throws IOException */ @Test public void demo1() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); IEmployeeDAO dao = session.getMapper(IEmployeeDAO.class); Employee employee = new Employee(); employee.setLastName("%呵%"); List<Employee> employees = dao.getConditionIf(employee); System.out.print(employees); session.close(); } }
1.4 动态SQL之更新
public void updateEmployee(Employee employee);
<update id="updateEmployee" > update employee <set> <if test="email != null"> email = #{email}, </if> <if test="lastName != null"> last_name = #{lastName} </if> <if test="gender != null"> gender = #{gender} </if> </set> where id = #{id} </update>
@Test public void demo1() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); IEmployeeDAO dao = session.getMapper(IEmployeeDAO.class); Employee employee = new Employee(); employee.setId(5); employee.setLastName("哈哈"); dao.updateEmployee(employee); session.commit(); session.close(); }
1.5 动态SQL--forEach
public List<Employee> getEmpsByConditionForEach(List<Integer> ids);
<select id="getEmpsByConditionForEach" resultType="cn.demo2.Employee" > select * from employee where id IN <foreach collection="list" item="item_id" separator="," open="(" close=")" > #{item_id} </foreach> </select>
/** * 测试查询 * @throws IOException */ @Test public void demo1() throws IOException { String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sqlSessionFactory.openSession(); IEmployeeDAO dao = session.getMapper(IEmployeeDAO.class); dao.getEmpsByConditionForEach(Arrays.asList(5,6,7)); session.close(); }
Mybatis(三)
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