I'm using ASP.NET MVC4 EF CodeFirst.
Need help to write LINQ (to entities) code in Index action to get collection of Courses which are attended by selected student. The relationship is many to many with join table with payload.
//StudentController
//-----------------------
public ActionResult Index(int? id)
{
var viewModel = new StudentIndexViewModel();
viewModel.Students = db.Students;
if (id != null)
{
ViewBag.StudentId = id.Value;
// *************PROBLEM IN LINE DOWN. HOW TO MAKE COURSES COLLECTION?
viewModel.Courses = db.Courses
.Include(i => i.StudentsToCourses.Where(t => t.ObjStudent.FkStudentId == id.Value));
}
return View(viewModel);
}
The error I got is:
The Include path expression must refer to a navigation property defined on the type. Use dotted paths for reference navigation properties and the Select operator for collection navigation properties.
I have modeles (the third one is for join table with payload):
//MODEL CLASSES
//-------------
public class Student
{
public int StudentId { get; set; }
public string Name { get; set; }
public virtual ICollection<StudentToCourse> StudentsToCourses { get; set; }
}
public class Course
{
public int CourseId { get; set; }
public string Title { get; set; }
public virtual ICollection<StudentToCourse> StudentsToCourses { get; set; }
}
public class StudentToCourse
{
public int StudentToCourseId { get; set; }
public int FkStudentId { get; set; }
public int FkCourseId { get; set; }
public string Classroom { get; set; }
public virtual Student ObjStudent { get; set; }
public virtual Course ObjCourse { get; set; }
}
Then, here is modelview I need to pass to view
//VIEWMODEL CLASS
//---------------
public class StudentIndexViewModel
{
public IEnumerable<Student> Students { get; set; }
public IEnumerable<Course> Courses { get; set; }
public IEnumerable<StudentToCourse> StudentsToCourses { get; set; }
}
EF does not support conditional include's. You'll need to include all or nothing (ie no Whereinside the Include)
If you need to get the data for just certain relations, you can select it into an anonymous type, something like (the obviously untested);
var intermediary = (from course in db.Courses
from stc in course.StudentsToCourses
where stc.ObjStudent.FkStudentId == id.Value
select new {item, stc}).AsEnumerable();
Obviously, this will require some code changes, since it's no longer a straight forward Course with a StudentsToCourses collection.
Related
I have joined and grouped 2 databases using linq in my controller, and now I need to parse it to the view. I know, I gonna need a ViewModel to do it, but I have no clue what to put in it, to make it work.
My Linq query in the controller looks like this:
var energyUsageViewModel =
from e in applicationDbContext
join u in _context.UsagesPerMonth on e.Id equals u.EnergyUsageId into u2
group u2 by new { Year = e.Year }
into u3
select u3.ToList();
return View(energyUsageViewModel);
In short what the linq query does is taking the "year" from table "e" joining it with table "u" which contains the energy usage per month, which I am gonna use to make a table in my view, which displays the year and usage per month in one row.
And currently my ViewModel looks like this (obviously not working):
public class EnergyUsageViewModel
{
public IEnumerable<UsagePerMonth> UsagePerMonthVm { get; set; }
}
The view takes a model of:
#model IEnumerable<Jullerup.Models.EnergyUsageViewModel>
I have tried to modify the ViewModel to take u3, but haven't succeeded.
I get the following invalid operation exception:
InvalidOperationException: The model item passed into the ViewDataDictionary is of type 'System.Linq.Enumerable+SelectEnumerableIterator2[System.Linq.IGrouping2[<>f__AnonymousType101[System.String],System.Collections.Generic.IEnumerable1[Jullerup.Models.UsagePerMonth]],System.Collections.Generic.List1[System.Collections.Generic.IEnumerable1[Jullerup.Models.UsagePerMonth]]]', but this ViewDataDictionary instance requires a model item of type 'System.Collections.Generic.IEnumerable`1[Jullerup.Models.EnergyUsageViewModel]'.
How do I edit my ViewModel to handle u3?
Update:
I'm working with 3 classes.
Customer class:
public class Customer
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
//Navigation Prop
public ICollection<EnergyUsage>? energyUsage { get; set; }
}
EnergyUsage class:
public class EnergyUsage
{
public int Id { get; set; }
public int CustomerID { get; set; }
public DateTime Date { get; set; }
public int YearlyHeatUsage { get; private set; }
public List<UsagePerMonth> UsagePerYear { get; set; }
//Navigation Prop
public Customer? Customer { get; set; }
}
UsagePerMonth class:
public class UsagePerMonth
{
public int Id { get; set; }
public MonthEnum Month { get; set; }
public int Usage { get; set; }
public int HeatUsage { get; private set; }
public string EnergyType { get; set; }
private EnergyMeasurement energyType { get; set; }
public int EnergyUsageId { get; set; }
}
In the database Customer.Id (PK) has a one to many relationship to EnergyUsage.CustomerId (FK) and EnergyUsage.Id (PK) has a one to many relationship to UsagePerMonth.EnergyUsageId (FK).
What I am trying to do, is to get an object/list something I can use in the view to display all instances of UsagePerMonth grouped by Customer.Year for a certain Customer.Id.
I saw some questions and answers about adding a value to a child when add/update the parent, but my question is the opposite.
I have a model Component with a parent-child relationship:
public class Component
{
public virtual int ComponentId { get; set; }
public virtual string Type { get; set; }
public virtual string Name { get; set; }
public virtual Course Course { get; set; }
public virtual int ParentId { get; set; }
public virtual Component Parent { get; set; }
public virtual List<Component> Childs { get; set; }
public virtual List<Evaluation> Evaluations { get; set; }
}
And i need to give a grade to each child to each user.
I have this model:
public class Evaluation
{
public virtual int EvaluationId { get; set; }
public virtual int ComponentId { get; set; }
public virtual Component Component { get; set; }
public virtual int UserCourseId { get; set; }
public virtual UserCourse User { get; set; }
public virtual int Grade { get; set; }
}
And a view that gets a component selected and allows to choose the user and give a grade. It's only allowed to give a grade to the last child, and the grade of their parent would be the same grade of the child (the ideia is in the future to have more childs and the grade of the parent would be the sum of their grade). So i need to create a new row on the database with the same grade but with the parent id of the component selected.
I tried this code but it doesn't work:
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(Evaluation evaluation)
{
if (ModelState.IsValid)
{
if (evaluation.Component.ParentId != 0)
{
var nota = new Evaluation
{
ComponentId = evaluation.Component.ParentId,
UserCourseId = evaluation.UserCourseId,
Grade = evaluation.Grade
};
db.Evaluations.Add(nota);
db.SaveChanges();
}
db.Evaluations.Add(evaluation);
db.SaveChanges();
return RedirectToAction("Index");
}
return View(evaluation);
}
(Note that this code can and probably is totally wrong)
How can i do this?
Thanks
After creating nota create a Component. something like this:
var nota = new Evaluation
{
ComponentId = evaluation.Component.ParentId,
UserCourseId = evaluation.UserCourseId,
Grade = evaluation.Grade
};
var component= new Component();
component.add(nota);
db.Components.Add(component);
db.SaveChanges();
You should see your nota also added to Evaluation table because of parent-child relationship.
I am trying my hands-on on mvc examples given on Mvc Offical Site.
Here i have 3 Models Student,Course and Enrollment where there is an one to many relationship on Course and Enrollment entities and many to one relationship on Enrollment and student.
The models for Student,Course and Enrollment are as follows with the navigation properties marked as "virtual" since i need to perform lazy binding
public class Student
{
public int StudentID { get;set; }
public string LastName { get; set; }
public string FirstMidName { get; set; }
public DateTime EnrollmentDate { get; set; }
public virtual IEnumerable<Enrollment> Enrollments { get; set; }
}
In the same way i have my course model
My Enrollment Model
public class Enrollment
{
public int EnrollmentID { get; set; }
public int CourseID { get; set; }
public int StudentID { get; set; }
// public Grade? Grade { get; set; }
public virtual Course Course { get; set; }
public virtual Student Student { get; set; }
}
I am using Code-First Technique With EF 5.My DB Context Class is as follows
public class SchoolContext:DbContext
{
public DbSet<Student> Students { get; set; }
public DbSet<Enrollment> Enrollments { get; set; }
public DbSet<Course> Courses { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
}
}
By Scaffolding I have generated all my views .On Click of my details Action link I have a controller function that is called
public ActionResult Details(int id = 0)
{
db.Configuration.LazyLoadingEnabled = true;
db.Configuration.ProxyCreationEnabled = true;
Student student = db.Students.Find(id);
// db.Entry(student).Reference(p => p.Enrollments).Load();
IEnumerable<Enrollment> s= student.Enrollments;
if (student == null)
{
return HttpNotFound();
}
return View(student);
}
Here the problem is when the Find() method is called in the controller the navigation property in Student Class model is null.But there is data in DB corresponding to the id that is being passed.In short,the navigation property is not returning data(null).
You have to materialize the entities to get a rid of the current lazy loading in the query:
Student student = db.Students.Find(id).ToList();
This will fix your problem without ToList() after db.Students.Find(id); = will returns the generated object from the dynamic proxy.
Second problem you have a casting bug:
IEnumerable<Enrollment> enrollments = student.Enrollments; // is wrong
should be:
ICollection<State> enrollments = student.Enrollments;
or
var enrollments = student.Enrollments;
Can someone explain to me how to use multiple models with a single view in which each of the models represent a DB table?
What I've currently done is created a model file for each model.
Example Model:
[Table("Order")]
public class OrderModel
{
[Key, Column(Order = 0)]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int OrderID { get; set; }
[Key, Column(Order = 1)]
public int UserID { get; set; }
public UserProfile Account { get; set; }
public DateTime Date { get; set; }
public int ShipLocation { get; set; }
public string PONumber { get; set; }
public int StatusID { get; set; }
public StatusModel Status { get; set; }
}
Here is the other model that encompases all the models to use in a single controller / view.
public class OrderPlacementModel
{
public OrderModel OrderChild { get; set; }
public OrderItemsModel OrderItemsChild { get; set; }
public StatusModel StatusChild { get; set; }
public MaterialsModel MaterialsChild { get; set; }
public CategoryModel CategoryChild { get; set; }
public PackModel PackChild { get; set; }
}
public ActionResult PlaceOrder()
{
var viewModel = new OrderPlacementModel
{
OrderChild = new OrderModel(),//or fetch this object from your data source
OrderItemsChild = new OrderItemsChild(),
//...etcetera
};
return View(viewModel);
}
Edit
Or, if you've strongly typed your view to a List<OrderPlacementModel> instead of a single instance, you could do something similar to this:
public ActionResult PlaceOrder()
{
var viewModel = new List<OrderPlacementModel>();
var model = new OrderPlacementModel
{
OrderChild = new OrderModel(),//or fetch this object from your data source
OrderItemsChild = new OrderItemsChild(),
//...etcetera
};
viewModel.Add(model);
//lather, rinse, repeat for however many instances you need to send to your view.
return View(viewModel);
}
Ideally, you should create a view model for the view that encompasses the fields from each model that you need to expose via the view. You can then map these in your controller. I would keep your mapping classes completely ignorant of your view models. Keep your views independent of your data model.
public class OrderViewModel
{
public int OrderId { get; set; }
public int UserId { get; set; }
public DateTime Date { get; set; }
public int ShippingLocation { get; set; }
public List<ItemViewModel> Items { get; set; }
}
public class ItemViewModel
{
public int ItemId { get; set; }
public int Title { get; set; }
}
Note how I have created a view model for the order and - to allow the order have multiple items - have separated these out into a separate model class. Now, you can type your view to OrderViewModel and use as many instances of ItemViewModel as your require.
You can then map your viewmodels to database entities from your controller:
[HttpPost]
public ActionResult ConfirmOrder (OrderViewModel model)
{
if (ModelState.IsValid)
{
foreach (ItemViewModel item in model.Items)
{
/* Create instance of OrderItemsModel (or whatever your
DB mapping class is), populate with appropriate data
from 'item' and commit to database. */
}
OrderModel order = new OrderModel();
order.OrderId = model.OrderId;
order.UserId = model.UserId;
order.Date = model.Date;
order.ShipLocation = model.ShippingLocation;
/* TODO: Commit new order to database */
}
}
Doing things this way adds a little overhead to your initial development time but allows you a great deal more flexibility as you aren't forced to mould all of your views to the shape of your entity classes.
I have set up 3 models, code first and the relationships seem to be working but one is causing me a problem.
I have Article, Language and Edition Classes
public class Article
{
public int ID { get; set; }
public string Name { get; set; }
public string Icon { get; set; }
}
public class Language
{
public int ID { get; set; }
public string Name { get; set; }
public string Code { get; set; }
}
public class Edition
{
public int ID { get; set; }
public Article Article { get; set; }
public Language Language { get; set; }
public string Title { get; set; }
public string Details { get; set; }
}
In my bootstrap/DBinitialiser, I can create Objects and populate them fine. The DB is created and the foreign keys for Language and Article are both present on the Edition table and correctly entered.
var engLang = new Language() {Code="en", Name="English Language"};
var altLang = new Language() {Code="xx", Name="Alternative Language"};
db.Languages.Add(engLang);
db.Languages.Add(altLang);
db.SaveChanges();
var testArt = new Article() { Name = "test" };
db.Articles.Add(testArt);
db.SaveChanges();
db.Editions.Add(new Edition(){Article = testArt, Language = engLang, Title="English Content"});
db.Editions.Add(new Edition(){Article = testArt, Language = altLang, Title="Alternative Content"});
db.SaveChanges();
I can now query the Editions and return a list of them, but the Language attribute is always NULL. The Article Attribute works fine.
var query = db.Editions.Where(r => r.Article.ID == Article.ID);
foreach (Edition item in query)
{
// item.Language => NULL
// item.Article => {Object Article}
}
I'm new to .net and Entity-Framework and can't work out why I always get this error.
I can even query by r => r.Language.ID == 1 and still get a NULL attribute on the Edition object.
Make sure you are using EF codefirst in right manner. Here you have some ambiguities. You must determine what relationships actually should exist, in your POCOs. Change classes like bellow:
public class Article
{
[Key]
public int ID { get; set; }
public string Name { get; set; }
public string Icon { get; set; }
}
public class Language
{
[Key]
public int ID { get; set; }
public string Name { get; set; }
public string Code { get; set; }
}
public class Edition
{
[Key]
public int ID { get; set; }
public virtual Article Article { get; set; }
public virtual Language Language { get; set; }
public string Title { get; set; }
public string Details { get; set; }
}
With thanks to AmirHossein Mehrvarzi for helping me write my models more clearly, I believe this error to be caused by the lazy loading of entities while iterating through the result of the query. ref: Entity Framework: There is already an open DataReader associated with this Command.
Without enabling MultipleActiveResultSets I simply added an Include statement to my linq
var query = db.Editions.Where(r => r.Article.ID == Article.ID).Include(r => r.Language);
foreach (Edition item in query)
{
// item.Language => {Object Language}
// item.Article => {Object Article}
}