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2x many-to-many queue from database using Entity Framework Core

This is where I struggle, for example, you have a setup up 2 x many-to-many relationship with Student in the center.
You have ClassID and HobbyID, how do you list all the students (+ all hobbies and classes in the collection inside student object) that have those using Entity Framework Core, and not have to access the database multiple times or to have to queue everything.
Thanks :)
Edit :
This is an example of what I want to achieve with minimum times accessing the database.
After you chose options on dropdowns (available information is ClassID and HobbyID) and click Filter button you should get students that have those. The students should be displayed with the rest of the classes and hobbies they have.
It is not possible to queue it all from single access to DB, how would you do it otherwise to be as effective as you can be.
Sorry if I was unclear. I am trying as hard as I can to explain this. Thank you for being patient! :)
Example design =>
<span>Pick a Hoby</span>
<select>
<option value="1">Climbing</option>
<option value="2">Running</option>
<option value="3">Painting</option>
</select>
<span style="margin-left:20px">Pick a Class</span>
<select >
<option value="1">Art</option>
<option value="2">Mathematics</option>
<option value="3">Geography</option>
</select>
<button>Filter</button>
<br>
<hr>
List of students :
<p>- <b>Mark</b> has <b>Hobbies : </b> Climbing, Painting / <b>Attending Classes : </b>: <b>Art</b>, Geography</p>
<p>- <b>Jhon</b> has <b>Hobbies : </b> Climbing / <b>Attending Classes : </b> Art</p>
<p>- <b>Steven</b> has <b>Hobbies : </b> Climbing, Running / <b>Attending Classes : </b> Art, Geography, Mathematics</p>

The following assumes EF Core 5, which now automatically creates many-to-many relationships without you having to add an entity class for the join table (as was necessary in previous versions of EF Core).
// Entity classes
public class Student
{
public int StudentId { get; set; }
public string StudentName { get; set; }
public ICollection<Hobby> Hobbies { get; set; }
public ICollection<Class> Classes { get; set; }
}
public class Class
{
public int ClassId { get; set; }
public string ClassName { get; set; }
public ICollection<Student> Students { get; set; }
}
public class Hobby
{
public int HobbyId { get; set; }
public string HobbyName { get; set; }
public ICollection<Student> Students { get; set; }
}
public class AppDbContext : DbContext
{
public AppDbContext(DbContextOptions<AppDbContext> options)
: base(options)
{
}
public DbSet<Student> Students { get; set; }
public DbSet<Class> Classes { get; set; }
public DbSet<Hobby> Hobbies { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Student>().HasKey(c => new { c.StudentId });
modelBuilder.Entity<Class>().HasKey(c => new { c.ClassId });
modelBuilder.Entity<Hobby>().HasKey(h => new { h.HobbyId });
}
}
Here's a simple controller action that uses a single EF Core 5 query statement in the get action to query for students along with their hobbies and classes included:
private readonly AppDbContext _dbContext;
public HomeController(AppDbContext dbContext, ILogger<HomeController> logger)
{
_dbContext = dbContext;
_logger = logger;
}
[HttpGet]
public IActionResult Index()
{
var students = _dbContext.Students
.Include(s => s.Hobbies)
.Include(s => s.Classes)
.ToList();
var filterableStudentListing = new FilterableStudentsListing
{
Students = students,
StudentClasses = students.SelectMany(s => s.Classes).Select(c => new SelectListItem { Text = c.ClassName, Value = c.ClassId.ToString() }).Distinct().ToList(),
StudentHobbies = students.SelectMany(s => s.Hobbies).Select(c => new SelectListItem { Text = c.HobbyName, Value = c.HobbyId.ToString() }).Distinct().ToList()
};
return View(filterableStudentListing);
}
[HttpPost]
public IActionResult Index(FilterableStudentsListing model)
{
// Demonstrates the new EF Core 5 filtered include, but you actually would not want to do this in a real app.
var students = _dbContext.Students
.Include(s => s.Hobbies.Where(h => h.HobbyId == model.SelectedHobbyId))
.Include(s => s.Classes.Where(c => c.ClassId == model.SelectedClassId))
.ToList();
var filterableStudentListing = new FilterableStudentsListing
{
Students = students,
StudentClasses = students.SelectMany(s => s.Classes).Select(c => new SelectListItem { Text = c.ClassName, Value = c.ClassId.ToString() }).Distinct().ToList(),
StudentHobbies = students.SelectMany(s => s.Hobbies).Select(c => new SelectListItem { Text = c.HobbyName, Value = c.HobbyId.ToString() }).Distinct().ToList()
};
return View(filterableStudentListing);
}
Clarifying on my code comment in the post action, the reason why it wouldn't be a good idea to use the EF Core Filtered Include in any real app, is you'd be stripping out possible select options for the user to choose each time you select a filter option to filter the data. In a real app, you would just filter the students in the view model after using the exact same query as in the get action. I just wanted to demo filtered include since its the new hotness in EF Core.
Here's a simple razor view that shows the students with their classes and hobbies:
#model FilterableStudentsListing
#{
ViewData["Title"] = "Home Page";
}
<div class="text-center">
<h1 class="display-4">Example</h1>
</div>
<div>
<form id="form1" method="post">
<select asp-for="SelectedClassId" asp-items="#Model.StudentClasses"> </select>
<select asp-for="SelectedHobbyId" asp-items="#Model.StudentHobbies"></select>
<button type="submit">Filter</button>
</form>
</div>
<div>
#foreach (var student in Model.Students)
{
<h4>#student.StudentName</h4>
<h5>Classes</h5>
<ul>
#foreach (var c in student.Classes)
{
<li>#c.ClassName</li>
}
</ul>
<h5>Hobbies</h5>
<ul>
#foreach (var h in student.Hobbies)
{
<li>#h.HobbyName</li>
}
</ul>
}
Here is the simple model class for the razor view:
public class FilterableStudentsListing
{
public List<Student> Students { get; set; }
public List<SelectListItem> StudentHobbies { get; set; }
public List<SelectListItem> StudentClasses { get; set; }
public int SelectedClassId { get; set; }
public int SelectedHobbyId { get; set; }
}

Razor Pages - EF return values of 2 tables

I have a database with 2 tables (clients and cars).
The table cars have a column named client_id.
In my Razor Pages project I have the models created for the 2 tables, but I need do a INNER JOIN to return the result to view side and do a foreach loop.
So until now I used the IList and do this in .cshtml:
#foreach (var item in Model.clients)
{
<p>#Html.DisplayFor(x=> item.name)</p>
<p>#Html.DisplayFor(x=> item.mail)</p>
}
And in code cshtm.cs
public IList<establishments> establishments;
IQueryable<establishments> establishments_filter;
establishments_filter = (from x in db.establishments where x.category == category select x);
establishments = establishments_filter.ToList();
Now the problem is that I cant do the same with a Inner Join or I don´t know how (most probably).
I see in others posts that I can use a variable to receive the values like this:
var filter = (from x in db.cars join y in db.clients on x.id_client == y.id select new {
mark = x.mark,
model = x.model,
name = y.name,
mail = y.name
}.ToList();
But now, my real question... How I can do a foreach if the var filter is not acessible in cshtml?
Thanks

I think you can define a viewModel that contains the field in the filter object. Then you can foreach the viewModel in your page. A simple demo like below:
Model:
public class Car
{
public int id { get; set; }
public string mark { get; set; }
public string model { get; set; }
[ForeignKey("Client")]
public int client_id { get; set; }
}
public class Client
{
public int id { get; set; }
public string name { get; set; }
public string mail { get; set; }
}
ViewModel:
public class ViewModel
{
public string Mark { get; set; }
public string Model { get; set; }
public string Name { get; set; }
public string Mail { get; set; }
}
Index.cshtml:
#page
#model RazorPageApp.Pages.IndexModel
#{
ViewData["Title"] = "Index";
}
<table>
<thead>
<tr>
<th>Mark</th>
<th>Model</th>
<th>Name</th>
<th>Mail</th>
</tr>
</thead>
#foreach (var item in Model.filter)
{
<tr>
<td>#Html.DisplayFor(x => item.Mark)</td>
<td>#Html.DisplayFor(x => item.Model)</td>
<td>#Html.DisplayFor(x => item.Name)</td>
<td>#Html.DisplayFor(x => item.Mail)</td>
</tr>
}
</table>
Index.cshtml.cs:
public class IndexModel : PageModel
{
private readonly ILogger<IndexModel> _logger;
private readonly MyDbContext _db;
public IndexModel(ILogger<IndexModel> logger, MyDbContext db)
{
_db = db;
_logger = logger;
}
public List<ViewModel> filter { get; set; }
public async Task OnGetAsync()
{
filter = await (from x in _db.cars
join y in _db.clients on x.client_id equals y.id
select new ViewModel
{
Mark = x.mark,
Model = x.model,
Name = y.name,
Mail = y.mail
}).ToListAsync();
}
DataSource:
Result:

How to populate multiple tags into input form in ASP.NET

I have a form which has a place where a user can insert multiple tags separated by a comma into the database. I got it to insert, but I'm having trouble retrieving it to show on my edit form.
This is my Edit Action:
public IActionResult Edit(int id)
{
var gallery = _ctx.GalleryImages.SingleOrDefault(m => m.Id == id);
if (gallery == null)
return NotFound();
var categories = _ctx.Categories.ToList();
var model = new GalleryFormViewModel(gallery)
{
Tags = gallery.Tags,
Category = categories,
};
return View("Views/Image/UploadForm.cshtml", model);
}
Here is my ViewModel:
public class GalleryFormViewModel
{
public int? Id { get; set; }
public string Title { get; set; }
public IEnumerable<ImageTag> Tags { get; set; }
public IEnumerable<Category> Category { get; set; }
[Required]
public int CategoryId { get; set; }
public IFormFile ImageUplaod { get; set; }
public GalleryFormViewModel()
{
Id = 0;
}
public GalleryFormViewModel(GalleryImage galleryImage)
{
Id = galleryImage.Id;
Title = galleryImage.Title;
Tags = galleryImage.Tags;
CategoryId = galleryImage.CategoryId;
}
}
And here is the Form input: (I'm using this form for creating and editing the gallery)
<div class="form-group">
#Html.LabelFor(m => m.Tags)
#Html.TextBoxFor(m => m.Tags, new { #class = "form-control" })
#Html.ValidationMessageFor(m => m.Tags)
</div>
Here is the Tag Model:
namespace SimpleImageGallery.Data.Models
{
public class ImageTag
{
public int Id { get; set; }
public string Description { get; set; }
}
}
Here is the Gallery Model:
public class GalleryImage
{
public virtual IEnumerable<ImageTag> Tags { get; set; }
// ....
}
This is how the tags table looks in the database:
It seems like I'm not getting any errors, maybe something is wrong in the actual input field?

There are some mistakes :
First, you have to Include the Tags to retrieve them from DB (if using Entity Framework):
var gallery = _ctx.GalleryImages.Include(m=>m.Tags).SingleOrDefault(m => m.Id == id);
Secondly, you are doing the same this twice :
var model = new GalleryFormViewModel(gallery)
{
Tags = gallery.Tags,
Category = categories,
};
and
public GalleryFormViewModel(GalleryImage galleryImage)
{
Id = galleryImage.Id;
Title = galleryImage.Title;
Tags = galleryImage.Tags;
CategoryId = galleryImage.CategoryId;
}
Thirdly, you cannot do this : #Html.TextBoxFor(m => m.Tags, new { #class = "form-control" }) for a enumerable, you have to reconstruct the string.

Inserting Data into Multiple Tables in MVC 4.5 using C#

I have these models
public class employee
{
public int Empid {get;set;}
public string name {get;set;}
public string fname{get;set;}
}
public class empLanguage
{
public string language { get; set; }
public string speaking{ get; set; }
}
public class EmpInsertion
{
public string name { get; set; }
public string fname { get; set; }
public List<ViewModels.Employee.empLanguage> EmpLangs { get; set; }
}
and i have this controller
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Insert(EmpInsertion empins)
{
if (ModelState.IsValid)
{
Employee Emp = new Employee();
Emp.name= empins.name;
Emp.fname= empins.fname;
var MaxID = (from emp in db.Employees select emp.EmployeeID).Max();
EmpLanguage objlng = new EmpLanguage();
objlng.EmployeeID = MaxID;
foreach (var emplang in Emp.EmpLanguages.ToList())
{
empLanguage lng = new empLanguage();
emplang.Language = lng.language;
emplang.Speaking = lng.speaking;
empins.EmpLangs.Add(lng);
}
}
}
I have two tables Employee(id, name, fname) Language(id, language, speaking, empid) it has one to many relationship, each employee can speak multiple language at same time.
I want to add data in both tables from one view, how can I add to one employee multiple language

I think you can do something like this.
public Employee CreatePartnerWithUser(Employee employee, List<Language> language)
{
using (DataContext context = new DataContext())
{
using (var trans = context.Database.BeginTransaction())
{
var insertEmployee = context.Employee.Add(employee);
context.SaveChanges();
var insertLanguage = context.Language.AddRange(language);
context.SaveChanges();
trans.Commit();
}
}
}

If use DbContext and EF change your model like this:
public class employee
{
public int id {get; set;}
public string name {get; set;}
public string fname {get; set;}
public virtual ICollection<language> language { get; set; }
}
public class language
{
public int id {get; set;}
public string languageName {get; set;}
public virtual ICollection<employee> employee { get; set; }
}
then in DbContext class add this modelBuilder to have many to many relations
modelBuilder.Entity<employee>()
.HasMany(e => e.language)
.WithMany(e => e.employee)
.Map(m => m.ToTable("employeeLanguage").MapLeftKey("employeeID").MapRightKey("languageID"));
after that, you can insert employee in a model like this:
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Insert(employee emp, string langs)
{
if (ModelState.IsValid)
{
using(DbContext db = new DbContext())
{
if(langs != null)
{
string[] strLangs = langs.Split('-');
foreach (var l in strLangs)
{
string lan = l.Trim();
while (lan.Contains(" "))
lan.Replace(" ", " ");
emp.language.Add(new language
{
languageName = lan
});
}
}
db.employee.Add(emp);
db.SaveChanges();
return View("YourReturnPage");
}
}
return View(Insert);
}
and in Insert.cshtml file adds this piece of code:
<div class="form-group">
<label for="Title" class="control-label col-md-2">Languages</label>
<div class="col-md-10">
<textarea type="text" name="langs" class="form-control" value="#ViewBag.langs"></textarea>
<p class="help-block text-danger">Separate language keywords with - </p>
</div>
</div>

C# MVC Entity Framework doesn't update List attribute of an object

I am making an auction application. Currently I am working on the bidding system. My Auction model consists of:
public class Auctions
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
(...) some more fields like title, description etc(...)
public List<Bid> bids = new List<Bid>(); // a list of bids from the users
}
public class Bid
{
public string bidAuthor { get; set; }
public decimal bid { get; set; }
public DateTime bidDate { get; set; }
}
In the view, I have a form for sending a bid:
#model BiddingViewModel
(...)info stuff about the auction(...)
#using (Html.BeginForm("CreateBid", "Auction", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
#Html.AntiForgeryToken()
#Html.HiddenFor(model=>model.auctionToSend.ID)
#Html.EditorFor(model => model.bid)
<input type="submit" value="Send a bid" />
}
Then, my contoller:
[Authorize]
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> CreateBid(BiddingViewModel bvm)
{
var user = await _userManager.FindByIdAsync(HttpContext.User.GetUserId());
var tmp = _context.Auctions.FirstOrDefault(i => i.ID == bvm.auctionToSend.ID);
Bid newBid = new Bid()
{
bid = decimal.Parse(bvm.bid.ToString()),
bidAuthor = user.Email,
bidDate = DateTime.Now
};
tmp.bids.Add(newBid);
_context.Entry(tmp).State = Microsoft.Data.Entity.EntityState.Modified;
_context.SaveChanges();
return RedirectToAction("AuctionList", "Auction");
}
Unfortunately, this doesn't seem to update my bids column in my database (which is of type VARBINARY(MAX)). What am I doing wrong?

I'll try to explain this as good as I can for the future users: the problem was that I tried to add the List as a column of the table. What I should have done was to add a new table for the Bids, linked in ApplicationDbContext:
public DbSet<Auctions> Auctions { get; set; }
public DbSet<Bid> Bids { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<Auctions>()
.HasOne(p => p.Signup)
.WithMany(b => b.Auction);
modelBuilder.Entity<Bid>()
.HasOne(p => p.Auction)
.WithMany(b => b.bids);
base.OnModelCreating(modelBuilder);
}
The rest was explained in Stephen Muecke's comments