I am building a Code-First, Many-To-Many relationship between my ApplicationUser class and a Lesson class. When the model is created, Entity Framework builds the two tables and the intersecting pivot table. However, neither table seems to take in data from the pivot table (LessonApplicationUsers). Both List variables do not seem to hold either the list of Students or the list of Lessons. Both entities i'm trying to marry up already exist in the database
ApplicationUser class
public class ApplicationUser : IdentityUser
{
public string Address { get; set; }
public int? Age { get; set; }
public ClassLevel? ClassLevel { get; set; }
public string FirstName { get; set; }
public int? Height { get; set; }
public string LastName { get; set; }
public string MobileNumber { get; set; }
public string Postcode { get; set; }
public string Town { get; set; }
public int? Weight { get; set; }
public ApplicationUser()
{
Lessons = new List<Lesson>();
}
public ICollection<Lesson> Lessons { get; set; }
}
Lesson Class
public class Lesson
{
[Key]
public int LessonID { get; set; }
public LessonType ClassType { get; set; }
public ClassLevel? ClassLevel { get; set; }
public DateTime ClassStartDate { get; set; }
public DateTime ClassEndDate { get; set; }
public float ClassCost { get; set; }
public int? InstructorID { get; set; }
public Lesson()
{
Students = new List<ApplicationUser>();
}
public ICollection<ApplicationUser> Students { get; set; }
public enum LessonType {Group,Private}
}
My DBContext
public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
public DbSet<Lesson> Lessons { get; set; }
public DbSet<ApplyViewModel> Applications { get; set; }
And finally, the code i'm using to add in the pivot table data. This is activated when the user presses a button on the booking form.
public ActionResult BookUser()
{
//Gather required variables
ApplicationUser user = db.Users.First(i => i.UserName == User.Identity.Name);
int classID = int.Parse(Request.Form["classID"]);
using (db)
{
var editedLesson = db.Lessons.Single(s => s.LessonID == classID);
db.Lessons.Attach(editedLesson);
var editedUser = db.Users.Single(s => s.Id == user.Id);
db.Users.Attach(editedUser);
editedLesson.Students.Add(editedUser);
db.SaveChanges();
}
return View("Index");
When I try and run it, when i press my book button, it runs through the code and executes. checking the database it has indeed inserted the key values into the pivot table. When i load the model of the lesson to view its details, the Student attribute has a count of 0. I've been at this for days and i've got the feeling i'm missing something kickself simple....but i've gone over it a dozen times and can't see what i'm doing wrong...
Mark your lists with virtual to enable lazy loading. Also is not required to initialize the lists Lessons = new List<Lesson>();
Related
I created local database using EF core and code-first method.
The db imitates library, so I have 3 simple tables: users, books and reservations.
Issue occurs when I want to get nested data like find one book and get its reservation.
I think I should be able to use
List<Reservation> reservations = book.Reservations;
but I have to use
List<Reservation> reservations = libraryContext.Reservations.
Where(r=> r.Book == book).ToList();
But the main reason I need help is this fragment
BookReservationsModel bookReservationsModel = new BookReservationsModel
{
BookTitle = book.Title,
Reservations = reservations
};
// I want to display emails in View.
for (int i = 0; i < bookReservationsModel.Reservations.Count; i++)
{
Debug.WriteLine(bookReservationsModel.Reservations[i].User.Email);
}
I cannot get access to users because they are nulls. In database everything is stored as it should be (correct ids). Of course I could copypaste certain emails to new created list but it's inefficient and I know I should be able to use it that way. I worked before with EF for Framework and I tried google the problem but couldn't find the solution.
Models and context code.
public class User
{
[Key]
public int UserID { get; set; }
[Required]
public string Name { get; set; }
[Required]
public string LastName { get; set; }
[Required]
public string Email { get; set; }
[Required]
public string Salt { get; set; }
[Required]
public string Password { get; set; }
public ICollection<Reservation> Reservations { get; set; }
}
public class Book
{
[Key]
public int BookID { get; set; }
[Required]
public string Title { get; set; }
[Required]
public string Author { get; set; }
[Required]
[DataType(DataType.Date)]
public DateTime PublishDate { get; set; }
[Required]
public string Description { get; set; }
public ICollection<Reservation> Reservations { get; set; }
}
public class Reservation
{
[Key]
public int ReservationID { get; set; }
[Required]
public DateTime ReservationDate { get; set; }
[Required]
public int UserID { get; set; }
[ForeignKey("UserID")]
public User User { get; set; }
[Required]
public int BookID { get; set; }
[ForeignKey("BookID")]
public Book Book { get; set; }
}
public class LibraryContext : DbContext
{
public LibraryContext(DbContextOptions options) : base(options) { }
public DbSet<User> Users { get; set; }
public DbSet<Book> Books { get; set; }
public DbSet<Reservation> Reservations { get; set; }
}
Attempting to use a navigation property on the book entity without doing either of the following will result in the property being null.
Including the property before materializing the entity with .First()/.Single()
https://learn.microsoft.com/en-us/ef/core/querying/related-data/eager
Configuring EFCore to AutoInclude navigation properties by default.
https://dotnetcoretutorials.com/2021/03/07/eager-load-navigation-properties-by-default-in-ef-core/
I suggest when querying for the book to use the Include and ThenInclude methods so the Reservations and Users are populated.
var book = await libraryContext.Books
.Include(x => x.Reservations)
.ThenInclude(x => x.User)
.SingleAsync(x => x.BookID == myBookId);
i am designing a system and one of my entity has one to many relation as shown below.
public class Product
{
public int Id { get; set; }
}
public class CompetitorProduct
{
public int Id { get; set; }
public Product Product { get; set; }
}
competitorProduct indicates that product has a equivalent which is sold by different store. should i define one-to-many relation as shown above or below? which one is correct?
public class Product
{
public int Id { get; set; }
public virtual ICollection<CompetitorProduct> CompetitorProducts{ get; set; }
}
public class CompetitorProduct
{
public int Id { get; set; }
}
Assuming it is a one to many relationship (what would happen if a competitor product was competing with more than one of your products for example) you can do both and add in a foreign key as well.
public class Product
{
public int Id { get; set; }
public virtual ICollection<CompetitorProduct> CompetitorProducts { get; set; }
}
public class CompetitorProduct
{
public int Id { get; set; }
public int ProductId { get; set; }
public virtual Product Product { get; set; }
}
You can then set up your relationship using fluent API as so:
modelBuilder.Entity<CompetitorProduct>(entity =>
{
entity.HasOne(e => e.Product)
.WithMany(e => e.CompetitorProducts)
.HasForeignKey(e => e.ProductId)
.HasConstraintName("FK_ComptetitorProduct_Product");
});
This way you can access the competitor products from the product and the product from the competitor products.
Here is a quick example of a ecommerce site I have worked on and how we did table relations.
I removed a bunch of the fields so you can see what you really need. Once to make relations and run Add-Migration EF will handle the FK constraints for you as long as you identified them in models like how I have below.
public class ApplicationUser : IdentityUser
{
public ApplicationUser()
{
Active = true;
CreateDateTimeUtc = DateTime.UtcNow;
ModifiedDateTimeUtc = DateTime.UtcNow;
}
[StringLength(500)]
public string FirstName { get; set; }
[StringLength(500)]
public string LastName { get; set; }
[StringLength(1000)]
public string Address { get; set; }
[StringLength(100)]
public string Unit { get; set; }
[StringLength(250)]
public string City { get; set; }
[StringLength(25)]
public string State { get; set; }
[StringLength(20)]
public string ZipCode { get; set; }
//This will give access to a list of child carts a user could have
[Index]
public bool Active { get; set; }
public virtual ICollection<Cart> Carts { get; set; }
// Account Profile Image
public byte[] ProfileImage { get; set; }
[StringLength(500)]
public string ProfileFilename { get; set; }
[StringLength(100)]
public string ProfileMimeType { get; set; }
}
[Table("Cart", Schema = "dbo")]
public class Cart : AbstractTable
{
public Cart()
{
IsComplete = false;
}
//This create relation to user table where I can get one unique user.
[StringLength(128)]
[ForeignKey("ApplicationUser")]
public string UserId { get; set; }
public virtual ApplicationUser ApplicationUser { get; set; }
//These link us to child tables of Cart where we can get a LIST of the items below
public virtual ICollection<CartCategory> CartCategories { get; set; }
public virtual ICollection<CartItem> CartItems { get; set; }
// Marked when a payment/receipt is generated based off of this cart
public bool IsComplete { get; set; }
}
[Table("CartItem", Schema = "dbo")]
public class CartItem : AbstractTable
{
//This will return one unique cart id and let us access it as the parent record
[ForeignKey("Cart")]
public Guid CartId { get; set; }
public virtual Cart Cart { get; set; }
// Signifies if this was paid for in a receipt
public bool IsComplete { get; set; }
public virtual ICollection<CartItemCustomField> CustomFields { get; set; }
}
I have created an MVC using Entity framework and I've encountered a situation which I don't know how to resolve.
I'm using the EF auto joins and relations (all my table models were created automatically by EF) .
Now for the problem - I have a table of customers, which has two(relavent) fields - personID and employerID . Only one of them contains data , the other will be null (a customer is either a person , or an employer) . When I try to include employer model in the result set, I'm getting thrown (without any message , when I debug I see that the content has data but the employeer is sometimes NULL) I'm also not sure about how the design should look like. This is my code :
Customer:
public partial class Customer
{
public Customer()
{
Account = new HashSet<Account>();
}
public long Id { get; set; }
public int? PersonId { get; set; }
public int Type { get; set; }
public int? EmployerId { get; set; }
public Employer Employer { get; set; }
public ICollection<Account> Account { get; set; }
}
Employer:
public partial class Employer
{
public Employer()
{
Customer = new HashSet<Customer>();
}
public int Id { get; set; }
public string Name { get; set; }
public int? IdType { get; set; }
public ICollection<Customer> Customer { get; set; }
}
Person:
public partial class Person
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public int Sex { get; set; }
public DateTime? BirthDate { get; set; }
public int IdType { get; set; }
}
Now when I'm running in my repository:
var collectionBeforePaging = _context.Customer
Everything works, but Employer is NULL. If I use :
var collectionBeforePaging = _context.Customer.Include(a => a.Employer)
Then the project fails .
How can I make this joins?
Please define ForeignKey for Customer
public int? EmployerId { get; set; }
[ForeignKey(nameof(EmployerId))]
public virtual Employer Employer { get; set; }
What version of EF you use? I think you missing something like that :
In Employer :
[ForeignKey("EmployerId")]
[InverseProperty("Customers")]
public virtual Employer Employer { get; set; }
public int? EmployerId { get; set; }
In Customer :
[InverseProperty("Employer")]
public virtual ICollection<Customer> Customers { get; set; }
It can also be done in the Dbontext object
I run into a little trouble understanding object relational mapping in MVC4 simple web application in which there are users and their posted comments.
One user must have a lot of comments. So I added in my UsersContext class public DbSet<UserWork> UserComments { get; set; }
public class UsersContext : DbContext
{
public UsersContext()
: base("DefaultConnection")
{
}
public DbSet<UserProfile> UserProfiles { get; set; }
public DbSet<UserWork> UserComments { get; set; }
}
[Table("UserProfile")]
public class UserProfile
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
public string UserName { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public int? UserComId { get; set; }
[ForeignKey("UserComId")]
public virtual UserComment UserComLog { get; set; }
}
public class UserComment
{
[Key]
public int UserComId{ get; set; }
public int UserId { get; set; }
public string Comments{ get; set; }
public DateTime postDate{get;set}
}
I am now stuck at realizing how all comments posted daily are stored such that I later can make a query like e.g SELECT * FROM UserComment Inner join UserProfile ON UserComment.UserId=UserProfile.UserId WHERE postDate BETWEEN (...) AND (...)
I'm assuming you're using Code First Migrations.
Seems like you need to edit your UserProfile class a little bit to allow for a user to have multiple comments. You need to make UserComLog a collection. Like:
public class UserProfile
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
public string UserName { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public virtual ICollection<UserComment> UserComLog { get; set; }
}
With that, you'll have a user with multiple comments. Then, with the UsersContext you can access the database tables that Entity Framework have created for you. You just need to use your data context to write a Linq statement to access the data.
var context = new UsersContext();
var comments = context.UserComments.Where(d => d.postDate > new DateTime(2013,3,12) && d.postDate < new DateTime(2013,2,12) && d.UserId == userId);
comments would be a IQueryable<UserComment> which you can then pass into a loop to display on a page, or filter further if you wish.
I have a working model, but have noticed that the relationship has been created twice in the database. Originally, it created two columns in the table, but with the addition of a specified foreign key attribute it has now just the one.
I have an Account class, which has many employers who can use the account. (one to many) Here are the classes:
public class Account
{
public int AccountId { get; set; }
[Required(ErrorMessage = Constants.ValidationMessages.FieldRequired)]
public string Name { get; set; }
public int? PrimaryUserId { get; set; }
[ForeignKey("PrimaryUserId")]
public Employer PrimaryUser { get; set; }
[ForeignKey("EmpAccountId")]
public ICollection<Employer> Employers { get; set; }
}
here is the inherited Employer class
public class Employer : User
{
public Employer()
{
DepartmentsToPost = new Collection<Department>();
Contacts = new Collection<Contact>();
}
[Display(Name = "Workplaces to advertise jobs")]
public virtual ICollection<Department> DepartmentsToPost { get; set; }
public int EmpAccountId { get; set; }
[ForeignKey("EmpAccountId")]
public virtual Account Account { get; set; }
public override string UserType
{
get { return "Employer"; }
}
}
User Table:
UserId
Username
FirstName
Surname
EmpAccountId
Discriminator
Account Table
AccountId
Name
PrimaryUserId
There is one link back to the User table - this is for the PrimaryUser field, and this is correct. There are two other relationships: Account -> Employers. EF has named them Account_Employers and Employer_Account. These are duplicates.
How can I prevent this occuring?
The Employers collection should be decorated with InversePropertyAttribute to point to the navigational property on the other side.
public class Account
{
public int AccountId { get; set; }
[Required(ErrorMessage = Constants.ValidationMessages.FieldRequired)]
public string Name { get; set; }
public int? PrimaryUserId { get; set; }
[ForeignKey("PrimaryUserId")]
public Employer PrimaryUser { get; set; }
[InverseProperty("Account")]
public ICollection<Employer> Employers { get; set; }
}