Select() 在 ThenInclude() 中不起作用

Posted 2023-04-01

【中文标题】Select() 在 ThenInclude() 中不起作用

【英文标题】：Select() does not work inside ThenInclude()

【发布时间】：2021-11-29 15:23:24

【问题描述】：

我正在尝试检索具有screenings 列表的movie 对象。 screenings 中的每个对象都有一个 theater 对象，而该对象又具有一个 screenings 列表。我试图摆脱theater 中的screenings 列表，所以我创建了一个theaterDTO 模型。

what I'm trying to achieve

    var x = _context.Movies
                .Where(m => movieId == m.Id)
                .Include(m => m.Screenings)

这会导致screening 列表被多次检索：在movie 对象和movie.theaters 中的每个theater 对象中

这是Screening 类：

public class Screening : BaseEntity
    
        public Theater Theater  get; set; 
        public Movie Movie  get; set; 
        public DateTime Time  get; set; 

        public ICollection<Booking> Bookings  get; set;     
        public Screening()
        
            Bookings = new List<Booking>();
        
    

Movie:

public class Movie : BaseEntity
    
        public string Name  get; set; 
        public string Body  get; set; 
        public string Dir  get; set; 
        public string Pic  get; set; 

        public ICollection<Screening> Screenings  get; set; 
        public Movie()
        
            Screenings = new List<Screening>();
        
    

Theater:

public class Theater : BaseEntity
    
        public string Address  get; set; 
        public string Name  get; set; 

        public ICollection<Screening> Screenings  get; set; 
        public Theater()
        
            Screenings = new List<Screening>();
        
    

TheaterDTO:

public class TheaterDTO 
    
        public string Address  get; set; 
        public string Name  get; set; 
    

功能：

[HttpGet]
    [Route("movieId")]
    public Movie GetMovieById(Guid movieId)
    
        return _context.Screenings
            .Where(m => movieId == m.Id)
            .Select(x => new TheaterDTO
            
                Name = x.Theater.Name,
                Address = x.Theater.Address
            ).FirstOrDefault();
    

【问题讨论】：

Theater 不是一个列表，它是一个对象。你想选择什么？

@Blindy movies 和 theaters 之间存在多对多关系，screenings 是桥接表。我正在尝试选择带有screenings 列表的电影对象。 screenings 中的每个对象都有一个 theater。我希望 theater 只有两列并省略其余列。

你能发布你的筛选课程吗？

@Serge 我已经添加了课程

谢谢，抱歉，您能否也添加剧院和电影

【参考方案1】：

首先定义一个 MovieDTO：

public class MovieDTO

    public string Name  get; set; 
    public string Body  get; set; 
    public string Dir  get; set; 
    public string Pic  get; set; 
    public List<ScreeningDTO> Screenings  get; set; 


public class ScreeningDTO

    public TheaterDTO Theater  get; set;  


public class TheaterDTO

    public string Address  get; set; 
    public string Name  get; set; 

这样的拍摄数据：

var x = _context.Movies
            .Where(m => movieId == m.Id)
            .Include(m => m.Screenings)
               .ThenInclude(s => s.Theater)
            .Where(p => p.Id == movieId)
            .Select(p => new MovieDTO 
                      Name = p.Name,
                      Body = p.Body,
                      Dir = p.Dir,
                      Pic = p.Pic,
                      Screening = p.Screenings.Select(x => new ScreeningDTO 
                                     Theater = new TheaterDTO 
                                        Name = x.Theater.Name,
                                        Address = x.Theater.Address
                                    
                       ).ToList()
                    ).FirstOrDefault();
               

【讨论】：

感谢您的回复。抛出此错误：CS0266: Cannot implicitly convert type "System.Linq.IQueryable<<anonymous type: System.Collections.Generic.IEnumerable<Data.Entities.TheaterDTO> Screening>>" to "Data.Entities.Movie"

好吧，也许编辑后的版本可以工作@user321

略有不同的错误：CS0266: Cannot implicitly convert type "System.Linq.IQueryable<<anonymous type: System.Collections.Generic.IEnumerable<<anonymous type: string Name, string Address>> Screening>>" to "Data.Entities.Movie"

哎呀，我忘了加ToList。再次检查@user321

这次是：CS0266: Cannot implicitly convert type "System.Collections.Generic.List<<anonymous type: System.Collections.Generic.List<<anonymous type: string Name, string Address>> Screening>>" to "Data.Entities.Movie"