@SelectProvider

package com.flying.entity;

public class StudentQuery {
    private String name;
    private String major;
    private Double minScore;

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getMajor() { return major; }
    public void setMajor(String major) { this.major = major; }
    public Double getMinScore() { return minScore; }
    public void setMinScore(Double minScore) { this.minScore = minScore; }
}

package com.flying.entity;

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String major;
    private Double score;

    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public Integer getAge() { return age; }
    public void setAge(Integer age) { this.age = age; }
    public String getMajor() { return major; }
    public void setMajor(String major) { this.major = major; }
    public Double getScore() { return score; }
    public void setScore(Double score) { this.score = score; }

    @Override
    public String toString() {
        return "Student{id=" + id + ", name='" + name + "', age=" + age +
               ", major='" + major + "', score=" + score + "}";
    }
}

package com.flying.provider;

import com.flying.entity.StudentQuery;
import org.apache.ibatis.jdbc.SQL;

public class StudentSqlProvider {

    /**
     * 根据动态条件构建查询 SQL
     */
    public String selectByCondition(final StudentQuery query) {
        return new SQL() {{
            SELECT("id, name, age, major, score");
            FROM("student");
            if (query.getName() != null && !query.getName().isEmpty()) {
                WHERE("name LIKE CONCAT('%', #{name}, '%')");
            }
            if (query.getMajor() != null && !query.getMajor().isEmpty()) {
                WHERE("major = #{major}");
            }
            if (query.getMinScore() != null) {
                WHERE("score >= #{minScore}");
            }
        }}.toString();
    }

    /**
     * MyBatis 3.5.1+ 可实现 ProviderMethodResolver 接口
     * 让方法名与 Mapper 方法名一致，从而省略 @SelectProvider 的 method 属性
     */
    public String selectByConditionProviderMethodResolver() {
        // 配合 ProviderMethodResolver 使用时的示例方法
        return "SELECT id, name, age, major, score FROM student";
    }
}

package com.flying.mapper;

import com.flying.entity.Student;
import com.flying.entity.StudentQuery;
import com.flying.provider.StudentSqlProvider;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.SelectProvider;
import java.util.List;

public interface StudentMapper {

    /**
     * 动态条件查询
     * type 指定 Provider 类，method 指定生成 SQL 的方法名
     */
    @SelectProvider(type = StudentSqlProvider.class, method = "selectByCondition")
    List<Student> selectByCondition(@Param("name") String name,
                                  @Param("major") String major,
                                  @Param("minScore") Double minScore);

    /**
     * 使用对象封装参数的动态查询
     */
    @SelectProvider(type = StudentSqlProvider.class, method = "selectByCondition")
    List<Student> selectByConditionObject(StudentQuery query);
}

package com.flying.test;

import com.flying.entity.Student;
import com.flying.entity.StudentQuery;
import com.flying.mapper.StudentMapper;
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 java.io.InputStream;
import java.util.List;

public class SelectProviderTest {
    public static void main(String[] args) throws Exception {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is);
        SqlSession session = factory.openSession();

        StudentMapper mapper = session.getMapper(StudentMapper.class);

        // 1. 只按名称模糊查询
        System.out.println("=== 只按名称查询 ===");
        List<Student> list1 = mapper.selectByCondition("小", null, null);
        list1.forEach(System.out::println);

        // 2. 按专业和最低分数查询
        System.out.println("\n=== 按专业和最低分数查询 ===");
        List<Student> list2 = mapper.selectByCondition(null, "计算机科学", 90.0);
        list2.forEach(System.out::println);

        // 3. 使用对象参数，三个条件都传
        System.out.println("\n=== 对象参数，多条件组合 ===");
        StudentQuery query = new StudentQuery();
        query.setName("大");
        query.setMajor("计算机科学");
        query.setMinScore(90.0);
        List<Student> list3 = mapper.selectByConditionObject(query);
        list3.forEach(System.out::println);

        // 4. 无条件查询
        System.out.println("\n=== 无条件查询 ===");
        List<Student> list4 = mapper.selectByCondition(null, null, null);
        list4.forEach(System.out::println);

        session.close();
    }
}