Mybatis使用注解实现复杂动态SQL的方法详解

import org.apache.ibatis.annotations.*;

@Mapper
public interface UserMapper {
    
    @Select("SELECT * FROM users WHERE name = #{name} AND age = #{age}")
    List<User> getUserByNameAndAge(@Param("name") String name, @Param("age") int age);
    
    @Update("UPDATE users SET name = #{name} WHERE id = #{id}")
    void updateUserNameById(@Param("id") int id, @Param("name") String name);
    
    @Insert("INSERT INTO users (name, age) VALUES (#{name}, #{age})")
    void insertUser(@Param("name") String name, @Param("age") int age);
    
    @Delete("DELETE FROM users WHERE id = #{id}")
    void deleteUserById(@Param("id") int id);
    
    // 更复杂的 SQL 可以通过 XML 方式或者动态 SQL 的注解方式实现
    // 也可以使用动态 SQL 注解 @SelectProvider、@UpdateProvider、@InsertProvider、@DeleteProvider 等
}

@Select("SELECT * FROM users WHERE 1=1 " +
        "<if test='ids != null'> " +
        "AND id IN <foreach collection='ids' item='id' open='(' separator=',' close=')'>#{id}</foreach> " +
        "</if>")
List<User> getUsersByIds(@Param("ids") List<Integer> ids);


  
 @Select({
        "SELECT * FROM users WHERE id IN ",
        "<foreach item='id' collection='userIds' open='(' separator=',' close=')'>",
            "#{id}",
        "</foreach>"
})
List<User> getUsersByIds(@Param("userIds") List<Integer> userIds);

public class UserSqlProvider {
    public String getUserByNameAndAge(Map<String, Object> params) {
        String name = (String) params.get("name");
        Integer age = (Integer) params.get("age");

        StringBuilder sb = new StringBuilder("SELECT * FROM users WHERE 1=1");
        
        if (name != null && !name.isEmpty()) {
            sb.append(" AND name = #{name}");
        }
        
        if (age != null) {
            sb.append(" AND age = #{age}");
        }
        return sb.toString();
    }
}

import org.apache.ibatis.annotations.*;

@Mapper
public interface UserMapper {
    @SelectProvider(type = UserSqlProvider.class, method = "getUserByNameAndAge")
    List<User> getUserByNameAndAge(Map<String, Object> params);
}