已解决映射问题

三个表，分别是movie(电影表），type（类型）和movie_type。

- 电影表

- 类型表

- movie_type表

- bean层

-movie

import java.util.List;

public class Movie {
    private Integer movieId;

    private String movieName;

    private  String pic;
     //从表实体包含一个主表实体的对象引用
    private List listType;

    public Integer getMovieId() {
        return movieId;
    }

    public void setMovieId(Integer movieId) {
        this.movieId = movieId;
    }

    public String getMovieName() {
        return movieName;
    }

    public void setMovieName(String movieName) {
        this.movieName = movieName;
    }

    public String getPic() {
        return pic;
    }

    public void setPic(String pic) {
        this.pic = pic;
    }

    public List getListType() {
        return listType;
    }

    public void setListType(List listType) {
        this.listType = listType;
    }

    @Override
    public String toString() {
        return "Movie{" +
                "movieId=" + movieId +
                ", movieName='" + movieName + ''' +
                ", pic='" + pic + ''' +
                ", listType=" + listType +
                '}';
    }

}

  -   type

import java.util.List;

public class Type {

    private Integer typeId;

    private String typeName;
     //
    private List listMovie;

   //set和get方法

    public Integer getTypeId() {
        return typeId;
    }

    public void setTypeId(Integer typeId) {
        this.typeId = typeId;
    }

    public String getTypeName() {
        return typeName;
    }

    public void setTypeName(String typeName) {
        this.typeName = typeName;
    }

    public List getListMovie() {
        return listMovie;
    }

    public void setListMovie(List listMovie) {
        this.listMovie = listMovie;
    }
    //toString方法
    @Override
    public String toString() {
        return "Type{" +
                "typeId=" + typeId +
                ", typeName='" + typeName + ''' +
                ", listMovie=" + listMovie +
                '}';
    }
}

- DAO层
 

public interface MovieDao {

//根据ID查电影
     List getMovieById(int id);
}

- mapper

 
       
       
       
       
        
           
       
   
   

    SELECT a.movie_id,
           a.movie_name,
           c.type_name typeName,
           a.movie_pic,
           
    FROM movie a
    LEFT JOIN movie_type b
    ON a.movie_id = b.movie_id
    LEFT JOIN type c
    ON b.type_id = c.type_id WHERe a.movie_id  =  #{movieId}

问题在这（  c.type_name typeName,）

- serviceImpl

@Service
public class MovieSerImpl implements MovieService {
    @Autowired
    private MovieDao movieDao;

    @Override
    public List getMovieId(int movieId) {
        return movieDao.getMovieById(movieId);
    }
}

-Test

@RunWith(SpringRunner.class)
@SpringBootTest
public class TestMovie {
    @Autowired
    MovieSerImpl movieSer;
@Test
    public void getSjService() {
     //设置要查找的电影id
    Integer a=1;
    //电影集合
    List list =movieSer.getMovieId(a);
    //集合长度
    int b= list.size();
    //输出集合长度
    System.out.println("list长度"+b);
    //遍历集合，并输出
    for (Movie movie:list){
        System.out.println(movie);
    }
       // System.out.println(movieSer.getMovieId(a));

    }
}

查询

list长度1
Movie{movieId=1, movieName='寒战', pic='movie——1', listType=[]}

结果

这里结果为空listType=[]

出现的原因是我复制

SELECT a.movie_id, a.movie_name,c.type_name typename ,a.movie_pic FROM movie a
     LEFT JOIN movie_type b ON a.movie_id = b.movie_id
     LEFT JOIN type c ON b.type_id = c.type_id WHERe a.movie_id = 1

SQL语句时候用了别名  typeName 导致我这个listType[]为空,现在将别名删去就正常有结果映射了。