This is a question about Models, ASP.NET MVC 3 and relationships. I'm using the code-first approach.
Imagine this simple typical scenario of an User with its Blog Posts:
public class User
{
public virtual int UserId { get; set; }
public virtual string Nickname { get; set; }
public virtual List<Post> Posts { get; set; }
}
public class Post
{
public virtual int PostId { get; set; }
public virtual string BlogText { get; set; }
}
I made it very very simple.
Well. When I create a controller using the Controller with Read/Write actions and views using Entity Framework, the collection of Posts is not considered. It's being ignored. So, I can't get this relationship to work.
If, in place of the collection, there was a single object (public virtual string Email, for example) it works normally.
I'm asking myself and to you:
Why
How do I put references to collections in my model?
It should be a simple task, I really can't understand why it doesn't work.
Thank you.
POCO should look like below to have one-to-many relationship:
public class Post
{
public int Id { get; set; }
public string BlogText { get; set; }
public virtual User User { get; set; }
}
public class User
{
public int Id { get; set; }
public string Nickname { get; set; }
public virtual ICollection<Post> Posts { get; set; }
}
Related
I am trying to implement code-first approach of entity framework. I have four entities UserInfo, Client, Admin and Account. I want relationships as:
Each Client has a UserInfo
Each Admin has a `UserInfo
Each Account is linked with a User(UserInfo)
Assuming these things i wrote the POCO models. With the relationships i want, is it correct ?Am i missing something?
public class UserInfo
{
public int UserInfoID { get; set; }
public Name Name { get; set; }
public Address Address { get; set; }
public Contact Contact { get; set; }
}
public class Admin
{
public int AdminID { get; set; }
public int UserInfoID { get; set; }
[ForeignKey("UserInfoID")]
public virtual UserInfo UserInfo { get; set; }
}
public class Client
{
public int ClientID { get; set; }
public CompanyDetails CompanyDetails { get; set; }
public int UserInfoID { get; set; }
[ForeignKey("UserInfoID")]
public virtual UserInfo UserInfo { get; set; }
}
public class Account
{
public int AccountID { get; set; }
[Required, Column("Balance"), Display(Name = "Account Balance")]
public double Balance { get; set; }
public int UserInfoID { get; set; }
[ForeignKey("UserInfoID")]
public virtual UserInfo UserInfo { get; set; }
}
What you have appears to be correct based on your requirements however I personally prefer the Entity Framework Model Builder when configuring your entities with Code First.
Using the model builder means that you don't have any attributes on your POCO entities which in turn means that you don't need an EF reference to use the entities.
Take a look at my article here for some more info on how to use the modelbuilder : http://blog.staticvoid.co.nz/2012/07/entity-framework-navigation-property.html
What I have is something like
public class BuildingUnit
{
public int ID { get; set; }
*irrelevant stuff removed*
public virtual BuildingUnitInsurance UnitInsurance { get; set; }
}
public class BuildingUnitInsurance
{
public int ID { get; set; }
*irrelevant stuff removed*
public virtual BuildingUnit BuildingUnit { get; set; }
}
What I want to do is have the relationship from the BuildingUnit to the BuildingUnitInsurance be optional, but if it does exist, the relationship from BuildingUnitInsurance to BuildingUnit must exist. I've tried a whole bunch of things with annotations and fluent api but I haven't really gotten anywhere.
The actual business case here is having a view displaying information from the BuildingUnit class, and then on that page it is possible to click a button and pop up a modal to add insurance information. Clicking the 'add insurance' button on that modal will post the insurance information to the controller and at that point it should be saved and the relationship should be created between the BuildingUnit and the BuildingUnitInsurance. Any help with the controller code would be great too since I don't really know what I would have to do there to make those relationships happen.
You need to have a one-to-zero-or-one relationship for BuildingUnit and a one-to-one required for BuildingUnitInsurance. The code below should help you and if not read more on Configuring Relationships.
public class BuildingUnit
{
[Key]
public int ID { get; set; }
[ForeignKey("UnitInsurance")]
public virtual int? UnitInsuranceId { get; set; }
public virtual BuildingUnitInsurance UnitInsurance { get; set; }
}
public class BuildingUnitInsurance
{
[Key]
public int ID { get; set; }
[Required]
[ForeignKey("BuildingUnit")]
public virtual int BuildingUnitId { get; set; }
public virtual BuildingUnit BuildingUnit { get; set; }
}
And then in your OnModelCreating handler:
modelBuilder.Entity<BuildingUnit>.HasOptional(x => x.UnitInsurance).WithRequired();
modelBuilder.Entity<BuildingUnitInsurance>.HasRequired(x => x.BuildingUnit).WithOptional();
I've been following the contoso university tutorial on Microsoft´s site and I have some doubts about how the Entity Framework is doing some stuff. Here we go...
On the beginning of the tutorial, we created three classes that will be turned into tables in my database.
I´d like to know when and how entity instantiates my classes to populate the objects.
Im using code-first approach.
Example:
The classes im using:
public class Course
{
public int CourseID { get; set; }
public string Title { get; set; }
public int Credits { get; set; }
public virtual ICollection<Enrollment> Enrollments { get; set; }
}
public class Enrollment
{
public int EnrollmentID { get; set; }
public int CourseID { get; set; }
public int StudentID { get; set; }
public decimal? Grade { get; set; }
public virtual Course Course { get; set; }
public virtual Student Student { get; set; }
}
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 ICollection<Enrollment> Enrollments { get; set; }
}
After following the tutorial I can now list all my Students and theirs respectives Course(s), as well as their properties in enrollments lists.
When did entity instantiated my Student classes and populated it with the respective Enrollment(s) lists?
How does it know what enrollments are linked to that student?
I dont see any new constructor() ever beeing called.
This might be simple but Im kinda lost here.
Thanks
It doesn't instantiate anything ahead of time, and it doesn't have to. And there won't be anything in the table representing the virtual property as such, either.
These virtual properties are used by EF at runtime to store navigation information, and the collections can be null or contain 0 or more elements. There's no magic, it's just by design that EF "new"s up the collection when it needs to.
If you want to be explicit about it, you can create a constructor on your POCO as well and set your collection equal to a new hashtable.
I'm trying to find out how I can re-use a simple 'Comment' entity type for multiple scenarios where something is 'commentable' in my application.
At the moment, I have a couple of entities that a user is able to post comments to. Examples include Blogs, Profiles and Photos - these can all be 'commented' on.
I'd like to be able to use the same 'Comment' class for each of these scenarios, but I don't want to end up with one HUGE table full of comments for everything. I figure it would be much more efficient to at least store a table of BlogComments, PhotoComments, and ProfileComments. At the moment, my Comment class looks like this:
public class Comment
{
[Key]
public int Id { get; set; }
public int ContextId { get; set; }
[StringLength(256)]
public string Content { get; set; }
public DateTime DatePosted { get; set; }
public virtual Member Author { get; set; }
}
Presumably, I'd need the 'ContextId' field to refer to the particular thing being commented on. This Id might be the Id of a Blog, a Profile or a Photo. I was hoping to be able to refer to comments much like a normal ICollection in these classes, and I have some code like this for the Photos as an example:
public class Photo
{
[Key]
public int Id { get; set; }
[StringLength(48)]
public string FileName { get; set; }
public virtual Member Owner { get; set; }
public virtual ICollection<Comment> Comments { get; set; }
}
I've been pointed to various articles during my searches, but none really seem relevant to my particular situation. How can I map these comment collections to different tables, and avoid having a comment "super-table"?
Any help, pointers or advice would be hugely appreciated :)
You can create an abstract Comment class and inherit from it specific comments such as PhotoComment, ProfileComment. You will be able to map the comments to different tables.
public abstract class Comment
{
[Key]
public int Id { get; set; }
[StringLength(256)]
public string Content { get; set; }
public DateTime DatePosted { get; set; }
public virtual Member Author { get; set; }
}
public class PhotoComment : Comment
{
public int PhotoId { get; set; }
public virtual Photo Photo { get; set; }
}
public class Photo
{
[Key]
public int Id { get; set; }
[StringLength(48)]
public string FileName { get; set; }
public virtual Member Owner { get; set; }
public virtual ICollection<PhotoComment> Comments { get; set; }
}
I'm having trouble passing view information from my Get/Create action to my view. Here are my three model classes;
public class Competition
{
public int Id { get; set; }
public int CompetitionId { get; set; }
public string Name { get; set; }
public string Prize { get; set; }
}
public class CompetitionEntry
{
public int Id { get; set; }
public int CompetitionEntryId { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public int CompetitionId { get; set; }
}
public class CompetitionEntryViewModel
{
public int Id { get; set; }
public Competition Competitions { get; set; }
public int CompetitionId { get; set; }
public string Name { get; set; }
public string Email { get; set; }
}
Here is my Get/Create action in CompetitionEntry Controller;
public ActionResult Create(int id)
{
CompetitionEntryViewModel competitionentryviewmodel = db.CompetitionEntriesView.Find(id);
return View(competitionentryviewmodel);
}
I know this doesn't work. The id parameter goes into the URL fine. How to I get access to my Competition class in th Get action? I need to be able to show the competion name on my Create Competition entry view.
Thanks in advance!
public ActionResult Create(int id)
{
var data = db.CompetitionEntriesView.Find(id);
CompetitionEntryViewModel competitionentryviewmodel = new CompetitionEntryViewModel();
competitionentryviewmodel.CompetitionName = data.Name;
return View(competitionentryviewmodel);
}
What you are trying to do is build an object graph and display it through a view model. In order to do this, you need to map your domain model(s) to your view model.
You can do the mapping yourself by writing a lot of code (re-inventing the wheel), or, you could consider using third party tools to do this for you. I recommend you use an AutoMapper as it is very simple to use imo.
The other problem is that your view model contains a domain model. This is likely to cause you a lot of headache in near future. If I were you, I would replace Competition with CompetitionViewModel.
I would also consider creating a view model for a list of competitions, i.e. CompetitionsViewModel. Look into partial views to see how you can display a list of competitions.
Good luck