[英]How to map a DTO with a many-to-many relationship to a EF core entity with a relationship table using automapper?
[英]Auto mapping (with AutoMapper) from DTO to an entity with many-to-many relationship in it
我遇到了以下示例中反映的問題。 我已經在BookController中創建了一個POST方法來創建Book實體:
這是我的代碼:
public class Book
{
public int BookId { get; set; }
public string Title { get; set; }
public virtual ICollection<BookCategory> BookCategories { get; set; }
}
public class BookCategory
{
public int BookId { get; set; }
public virtual Book Book { get; set; }
public int CategoryId { get; set; }
public virtual Category Category { get; set; }
}
我的DTO:
public class BookDto
{
public int BookId { get; set; }
public string Title { get; set; }
public ICollection<CategoryDto> Categories { get; set; }
}
public class CategoryDto
{
public int CategoryId { get; set; }
public string CategoryName { get; set; }
}
自動映射器配置:
CreateMap<Book, BookDto>().ReverseMap();
CreateMap<BookCategory, CategoryDto>()
.ForMember(d => d.CategoryId, opt => opt.MapFrom(s => s.CategoryId))
.ForMember(d => d.CategoryName, opt => opt.MapFrom(s => s.Category.CategoryName));
CreateMap<CategoryDto, BookCategory>().ForMember(d => d.CategoryId, opt => opt.MapFrom(s => s.CategoryId));
CreateMap<BookDto, Book>().AfterMap((s, d) =>
{
foreach (var bookCategory in d.BookCategories)
{
bookCategory.BookId = s.BookId;
}
});
這是我要映射到實體的DTO:
BookDto model = new BookDto()
{
Title = "Test book",
Categories = new List<CategoryDto>()
{
new CategoryDto()
{
CategoryId = 1,
CategoryName = "drama"
}
},
};
BookDto是一本新書,但是它指向現有的類別。 在數據庫中已經存在Category.Id = 1,其中“ drama”作為CategoryName。 當前問題在於映射:
CreateMap<BookDto, Book>().AfterMap((s, d) =>
{
foreach (var bookCategory in d.BookCategories)
{
bookCategory.BookId = s.BookId;
}
});
當上面的代碼即將執行時,d.BookCategories為null。 所以我想知道我的映射有什么問題嗎?
AutoMapper自動映射具有相同名稱的成員。 由於Book
和BookDto
集合具有不同的名稱( BookCategories
與Categories
),因此必須對其進行顯式映射。 您可以在其中一張地圖中執行此操作,而ReverseMap
將處理相反的情況:
CreateMap<Book, BookDto>()
.ForMember(d => d.Categories, opt => opt.MapFrom(s => s.BookCategories))
.ReverseMap()
.AfterMap((s, d) =>
{
foreach (var bookCategory in d.BookCategories)
bookCategory.BookId = s.BookId;
});
但是由於BookCategory
實體僅包含2個id,因此可以避免從CategoryDto
到BookCategory
和AfterMap
的映射,並使用簡單的LINQ投影(`Select')進行反向映射:
CreateMap<Book, BookDto>()
.ForMember(d => d.Categories, opt => opt.MapFrom(s => s.BookCategories))
.ReverseMap()
.ForMember(d => d.BookCategories, opt => opt.MapFrom(s => s.Categories
.Select(c => new BookCategory { BookId = s.BookId, CategoryId = c.CategoryId })));
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