How do you access a models related properties using Entity Framework? [closed]

问题

I'm developing a simple application that will allow users to create a profile and upload multiple images. I'm using ASP.NET Identity and will therefore refer to "user" as ApplicationUser. I have an Image and an ApplicationUser domain model shown below:

    public class ApplicationUser : IdentityUser
    {
        public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
        {
            // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
            var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
            // Add custom user claims here
            return userIdentity;
        }
        public string UserFirstName { get; set; }
        public string UserSurname { get; set; }
        public string City { get; set; }
        public virtual ICollection<Image> Image { get; set; }
    }

And

    public class Image
    {
        public int ImageID { get; set; }
        public string ImageCaption { get; set; }
        public int NumOfLikes { get; set; }
        public string ImageFilePath { get; set; }
        //[ForeignKey("ApplicationUser")]
        //public int ApplicationUserID { get; set; }
        public virtual ApplicationUser ApplicationUser { get; set; }
    }

I added public virtual ICollection<Image> Image { get; set; } and public virtual ApplicationUser ApplicationUser { get; set; } to define a one-to-many relationship between ApplicationUser and Image. After running the application I noticed that Entity Framework had created ApplicationUser_id in the Images table (Which I assume I can use as a foreign key without having to uncomment the code in the Image domain model).

I also have ViewImagesViewModel which will return to a view, a collection of images which I would like to be able to filter and sort by ApplicationUser's name,surname and city. My problem is that I don't know how to combine the properties from both domain models into a single view model.

Questions

How do I access or return ApplicationUser's properties when returning Image?
How do I bind Image's related attributes such as ApplicationUser's UserFirstName to ViewImagesViewModel?

回答1:

To get the required data 'eagerly loaded' into one model, you can use Include

When fetching an image, you can also fetch the user:

var image = context.Images.Include(i => i.ApplicationUser).FirstOrDefault(i => i.ImageId == imageId);

or the reverse, when fetching a user you can fetch all images for that user:

var user = context.ApplicationUser.Include(u => u.Image).FirstOrDefault(u => u.Id == userId);

After that, you can access image.ApplicationUser.UserSurname. See this MSDN article

回答2:

as you said you have a ViewImagesViewModel, so I thought that this viewmodel should be something like that

public class ViewImagesViewModel 
{
    public void ViewImagesViewModel() 
    {
        this.Images = new List<ViewImageViewModel>();
    }

    public string UserFirstName { get; set; }
    public string UserSurname { get; set; } 
    public string City { get; set; }

    public List<ViewImageViewModel> Images { get; set; }
}

public class ViewImageViewModel
{
    public string ImageUrl { get; set; }
    public int Likes { get; set; }
    public string Caption { get; set; }
}

and below is how you could map the domain entities to your viewmodel, in the controller action do it like that

...
var entity = db.ApplicationUsers.FirstOrDefault(x => x.Id == 1);

if (entity != null) 
{
    var model = new ViewImagesViewModel();
    model.UserFirstName = entity.UserFirstName;
    model.UserSurname = entity.UserSurname;
    model.City = entity.City;

    // fix the Image property in the ApplicationUser entity to be Images instead of Image as it represent a collection
    foreach (var img in entity.Images)
    {
        var imgModel = new ViewImageViewModel()
        {
            // you may change this to get the correct Url
            ImageUrl = string.Concat(HttpContext.Request.Url.Scheme, 
                  "://", HttpContext.Request.Url.Host, 
                  HostingEnvironment.ApplicationVirtualPath,
                  img.ImageFilePath),
            Likes = img.NumOfLikes,
            Caption = img.Caption
        };

        model.Images.Add(imgModel);
    }

    return View(model);
}
...

来源：https://stackoverflow.com/questions/33103210/how-do-you-access-a-models-related-properties-using-entity-framework

标签

ASP.NET

asp.net-mvc

entity-framework

asp.net-identity