I see this a lot in tutorials, with navigation properties as `ICollection&lt;T&gt;`.

Is this a mandatory requirement for Entity Framework? Can I use `IEnumerable`?

What&#39;s the main purpose of using `ICollection` instead of `IEnumerable` or even `List&lt;T&gt;`?

Why use ICollection and not IEnumerable or List&lt;T&gt; on many-many/one-many relationships?

I want to save my Edit to Database and I am using Entity FrameWork Code-First in ASP.NET MVC 3 / C# but I am getting errors. In my Event class, I have DateTime and TimeSpan datatypes but in my database, I&#39;ve got Date and time respectively. Could this be the reason? How can I cast to the appropriate datatype in the code before saving changes to database.

    public class Event
    {
        public int EventId { get; set; }
        public int CategoryId { get; set; }
        public int PlaceId { get; set; }
        public string Title { get; set; }
        public decimal Price { get; set; }
        public DateTime EventDate { get; set; }
        public TimeSpan StartTime { get; set; }
        public TimeSpan EndTime { get; set; }
        public string Description { get; set; }
        public string EventPlaceUrl { get; set; }
        public Category Category { get; set; }
        public Place Place { get; set; }
    }

Method in the controller &gt;&gt;&gt;&gt; Problem at storeDB.SaveChanges();

    // POST: /EventManager/Edit/386        
    [HttpPost]
    public ActionResult Edit(int id, FormCollection collection)
    {
        var theEvent = storeDB.Events.Find(id);

        if (TryUpdateModel(theEvent))
        {
            storeDB.SaveChanges();
            return RedirectToAction(&quot;Index&quot;);
        }
        else
        {
            ViewBag.Categories = storeDB.Categories.OrderBy(g =&gt; g.Name).ToList();
            ViewBag.Places = storeDB.Places.OrderBy(a =&gt; a.Name).ToList();
            return View(theEvent);
        }
    }

with 

    public class EventCalendarEntities : DbContext
    {
        public DbSet&lt;Event&gt; Events { get; set; }
        public DbSet&lt;Category&gt; Categories { get; set; }
        public DbSet&lt;Place&gt; Places { get; set; } 
    }

SQL Server 2008 R2 Database / T-SQL  

    EventDate (Datatype = date)  
    StartTime (Datatype = time)  
    EndTime (Datatype = time)  

Http Form  
  
    EventDate (Datatype = DateTime) e.g. 4/8/2011 12:00:00 AM  
    StartTime (Datatype = Timespan/time not sure) e.g. 08:30:00  
    EndTime (Datatype = Timespan/time not sure) e.g. 09:00:00  


Server Error in &#39;/&#39; Application.

Validation failed for one or more entities. See &#39;EntityValidationErrors&#39; property for more details.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Data.Entity.Validation.DbEntityValidationException: Validation failed for one or more entities. See &#39;EntityValidationErrors&#39; property for more details.

Source Error: 


    Line 75:             if (TryUpdateModel(theEvent))
    Line 76:             {
    Line 77:                 storeDB.SaveChanges();
    Line 78:                 return RedirectToAction(&quot;Index&quot;);
    Line 79:             }

Source File: C:\sep\MvcEventCalendar\MvcEventCalendar\Controllers\EventManagerController.cs       Line: 77 

Stack Trace: 


[DbEntityValidationException: Validation failed for one or more entities. See &#39;EntityValidationErrors&#39; property for more details.]

Validation failed for one or more entities while saving changes to SQL Server Database using Entity Framework

I&#39;ve just started using EF code first, so I&#39;m a total beginner in this topic.

I wanted to create relations between Teams and Matches:

1 match = 2 teams (home, guest) and result. 

I thought it&#39;s easy to create such a model, so I started coding:

    public class Team
    {
        [Key]
        public int TeamId { get; set;} 
        public string Name { get; set; }

        public virtual ICollection&lt;Match&gt; Matches { get; set; }
    }
   

    public class Match
    {
        [Key]
        public int MatchId { get; set; }

        [ForeignKey(&quot;HomeTeam&quot;), Column(Order = 0)]
        public int HomeTeamId { get; set; }
        [ForeignKey(&quot;GuestTeam&quot;), Column(Order = 1)]
        public int GuestTeamId { get; set; }

        public float HomePoints { get; set; }
        public float GuestPoints { get; set; }
        public DateTime Date { get; set; }

        public virtual Team HomeTeam { get; set; }
        public virtual Team GuestTeam { get; set; }
    }

And I get an exception: 

&gt; The referential relationship will result in a cyclical reference that is not allowed. [ Constraint name = Match_GuestTeam ]

How can I create such a model, with 2 foreign keys to the same table?

Entity Framework Code First - two Foreign Keys from same table

The error message :

&gt;&quot;The model backing the &#39;AddressBook&#39; context has changed since the database was created.  Either manually delete/update the database, or call Database.SetInitializer with an IDatabaseInitializer instance.  For example, the RecreateDatabaseIfModelChanges strategy will automatically delete and recreate the database, and optionally seed it with new data.&quot;


 I am trying to use the code-first feature and following is what I wrote:

    var modelBuilder = new ModelBuilder();
    var model = modelBuilder.CreateModel();
    using (AddressBook context = new AddressBook(model))
    {
        var contact = new Contact
        {
            ContactID = 10000,
            FirstName = &quot;Brian&quot;,
            LastName = &quot;Lara&quot;,
            ModifiedDate = DateTime.Now,
            AddDate = DateTime.Now,
            Title = &quot;Mr.&quot;
    
        };
        context.contacts.Add(contact);
        int result = context.SaveChanges();
        Console.WriteLine(&quot;Result :- &quot;+ result.ToString());
    }

The context class:

    public class AddressBook : DbContext
    {
        public AddressBook()
        { }
        public AddressBook(DbModel AddressBook)
            : base(AddressBook)
        {
    
        }
        public DbSet&lt;Contact&gt; contacts { get; set; }
        public DbSet&lt;Address&gt; Addresses { get; set; }
    }

and the connection string:

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot; ?&gt;
    &lt;configuration&gt;
        &lt;connectionStrings&gt;
        &lt;add name=&quot;AddressBook&quot; providerName=&quot;System.Data.SqlClient&quot;  
             connectionString=&quot;Data Source=MyMachine;Initial Catalog=AddressBook;
             Integrated Security=True;MultipleActiveResultSets=True;&quot;/&gt;
        &lt;/connectionStrings&gt;
    &lt;/configuration&gt;

So, the database name is &quot;AddressBook&quot; and the error happens when I trying to add the contact object to the context. Am I missing anything here?

The model backing the &lt;Database&gt; context has changed since the database was created

**Question**

Is it possible to define a unique constraint on a property using either the fluent syntax or an attribute? If not, what are the workarounds?

I have a user class with a primary key, but I would like to make sure the email address is also unique. Is this possible without editing the database directly?


**Solution (based on Matt&#39;s answer)**

	public class MyContext : DbContext {
		public DbSet&lt;User&gt; Users { get; set; }

		public override int SaveChanges() {
			foreach (var item in ChangeTracker.Entries&lt;IModel&gt;())
				item.Entity.Modified = DateTime.Now;

			return base.SaveChanges();
		}

		public class Initializer : IDatabaseInitializer&lt;MyContext&gt; {
			public void InitializeDatabase(MyContext context) {
				if (context.Database.Exists() &amp;&amp; !context.Database.CompatibleWithModel(false))
					context.Database.Delete();

				if (!context.Database.Exists()) {
					context.Database.Create();
					context.Database.ExecuteSqlCommand(&quot;alter table Users add constraint UniqueUserEmail unique (Email)&quot;);
				}
			}
		}
	}

Unique Constraint in Entity Framework Code First

Is it possible to have Entity Framework (I am using the Code First Approach with CTP5 currently) store all DateTime values as UTC in the database?

Or is there maybe a way to specify it in the mapping, for example in this one for the last_login column:

    modelBuilder.Entity&lt;User&gt;().Property(x =&gt; x.Id).HasColumnName(&quot;id&quot;);
    modelBuilder.Entity&lt;User&gt;().Property(x =&gt; x.IsAdmin).HasColumnName(&quot;admin&quot;);
    modelBuilder.Entity&lt;User&gt;().Property(x =&gt; x.IsEnabled).HasColumnName(&quot;enabled&quot;);
    modelBuilder.Entity&lt;User&gt;().Property(x =&gt; x.PasswordHash).HasColumnName(&quot;password_hash&quot;);
    modelBuilder.Entity&lt;User&gt;().Property(x =&gt; x.LastLogin).HasColumnName(&quot;last_login&quot;);

Entity Framework DateTime and UTC

I&#39;ve watched several presentations of EF Code First and haven&#39;t seen how EFCF works with stored procedures.

How can I declare a method that will use some sp? Can I pass an entity to a method that calls sp without manually mapping entity properties to sp parameters?

Also, what happens if I change my model? Would it drop my sp while recreating table from model? And what about triggers?

If these things are not supported, are there any plans to support them in future?

Does Entity Framework Code First support stored procedures?

I&#39;m creating a POCO model to use with entity framework code first CTP5.  I&#39;m using the &lt;key()&gt; decoration to make a property map to a PK column.  But how can I define a PK on more then one column, and specifically, how can I control order of the columns in the index?  Is it a result of the order of properties in the class?

Thanks!

in entity framework code first, how to use KeyAttribute on multiple columns

I have an Entity and I am to configure Entity Framework to map it to a database table with different name.

I can easily do this with **[Code First DataAnnotations][1]** (**DataAnnotations.Schema.TableAttribute**).

But due to limitations now I have to use **[Code First Fluent API][2]** (my domain objects will be used by external clients, so they shouldn&#39;t be technology-specific - e.g. have any references to DataAnnotations)

I&#39;ve searched on MSDN but found nothing. So is it possible and how?

Thank you.

  [1]: https://docs.microsoft.com/en-us/ef/ef6/modeling/code-first/data-annotations
  [2]: http://msdn.microsoft.com/en-us/data/jj591620.aspx

How to specify table name with Entity Framework Code First Fluent API

How can I use the database view in entity framework code first,


how to use views in code first entity framework

I am using Entity Framework Code First method to create my database table. The following code 
creates a `DATETIME` column in the database, but I want to create a `DATE` column.    

    [DataType(DataType.Date)]
    [DisplayFormatAttribute(ApplyFormatInEditMode = true, DataFormatString = &quot;{0:d}&quot;)]
    public DateTime ReportDate { get; set; }

How can I create a column of type `DATE`, during table creation?


Entity Framework Code First Date field creation

Using the data annotation `Required` like so:

    [Required]
    public int somefield {get; set;}

Will set &lt;b&gt;somefield&lt;/b&gt; to `Not Null` in database, How can I set &lt;b&gt;somefield&lt;/b&gt;
to allow NULLs?, I tried setting it through SQL Server Management Studio but Entity Framework set it back to *`Not Null`*.

Nullable property to entity field, Entity Framework through Code First

I have a code-first entity model in EF5. But I want to manage the database changes manually -- I do not want EF to modify my existing database and all its data. But when I make parallel changes in the EF mapping and in the database, EF refuses to operate properly telling me I need to use code first migration.  How do I turn this off?

How can I disable code first migrations

I am trying to do this:

    ALTER TABLE CompanyTransactions DROP COLUMN Created

But I get this:

&gt;Msg 5074, Level 16, State 1, Line 2
The object &#39;DF__CompanyTr__Creat__0CDAE408&#39; is dependent on column &#39;Created&#39;.
Msg 4922, Level 16, State 9, Line 2
ALTER TABLE DROP COLUMN Created failed because one or more objects access this column.

This is a code first table.  Somehow the migrations have become all messed up and I am trying to manually roll back some changed.

I have *no* idea what this is:

    DF__CompanyTr__Creat__0CDAE408

ALTER TABLE DROP COLUMN failed because one or more objects access this column

Is there a way to decorate your POCO classes to automatically eager-load child entities without having to use `Include()` every time you load them? 

Say I have a Class Car, with Complex-typed Properties for Wheels, Doors, Engine, Bumper, Windows, Exhaust, etc. And in my app I need to load my car from my DbContext 20 different places with different queries, etc. I don&#39;t want to have to specify that I want to include all of the properties every time I want to load my car. 

I want to say 

    List&lt;Car&gt; cars = db.Car
                    .Where(x =&gt; c.Make == &quot;Ford&quot;).ToList();
    
    //NOT .Include(x =&gt; x.Wheels).Include(x =&gt; x.Doors).Include(x =&gt; x.Engine).Include(x =&gt; x.Bumper).Include(x =&gt; x.Windows)
    
    
    foreach(Car car in cars)
    {
    
    //I don&#39;t want a null reference here.
    
    String myString = car.**Bumper**.Title;
    }

Can I somehow decorate my POCO class or in my `OnModelCreating()` or set a configuration in EF that will tell it to just load all the parts of my car when I load my car? I want to do this eagerly, so my understanding is that making my navigation properties virtual is out. I know NHibernate supports similar functionality. 

Just wondering if I&#39;m missing something. Thanks in advance!

Cheers,

Nathan


I like the solution below, but **am wondering if I can nest the calls to the extension methods.** For example, say I have a similar situation with Engine where it has many parts I don&#39;t want to include everywhere. Can I do something like this? (I&#39;ve not found a way for this to work yet). This way if later I find out that Engine needs FuelInjectors, I can add it only in the BuildEngine and not have to also add it in BuildCar. **Also if I can nest the calls, how can I nest a call to a collection? Like to call BuildWheel() for each of my wheels from within my BuildCar()?**

    public static IQueryable&lt;Car&gt; BuildCar(this IQueryable&lt;Car&gt; query) {
         return query.Include(x =&gt; x.Wheels).BuildWheel()
                     .Include(x =&gt; x.Doors)
                     .Include(x =&gt; x.Engine).BuildEngine()
                     .Include(x =&gt; x.Bumper)
                     .Include(x =&gt; x.Windows);
    }
    
    public static IQueryable&lt;Engine&gt; BuildEngine(this IQueryable&lt;Engine&gt; query) {
         return query.Include(x =&gt; x.Pistons)
                     .Include(x =&gt; x.Cylendars);
    }

    //Or to handle a collection e.g.
     public static IQueryable&lt;Wheel&gt; BuildWheel(this IQueryable&lt;Wheel&gt; query) {
         return query.Include(x =&gt; x.Rim)
                     .Include(x =&gt; x.Tire);
    }


Here is another very similar thread in case it is helpful to anyone else in this situation, but it still doesn&#39;t handle being able to make nexted calls to the extension methods.

https://stackoverflow.com/questions/3356541/entity-framework-linq-query-include-multiple-children-entities


Entity Framework - Is there a way to automatically eager-load child entities without Include()?

I use code-first in my project and deploy on host but I get error

&gt; CREATE DATABASE permission denied in database &#39;master&#39;.

This is my connection string:

    &lt;add name=&quot;DefaultConnection&quot; 
         connectionString=&quot;Data Source=.\SQLEXPRESS;Initial Catalog=aspnet-test-2012615153521;Integrated Security=False&quot; 
         providerName=&quot;System.Data.SqlClient;User ID=test;Password=test&quot;/&gt;

 


CREATE DATABASE permission denied in database &#39;master&#39; (EF code-first)

Well, I have one-to-many related model:

    public class Parent
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public ICollection&lt;Child&gt; Children { get; set; }
    }
    
    public class Child
    {
        public int Id { get; set; }
        public string ChildName { get; set; }
    }

What I want to do is clear `Parent.Children` and remove related child entities from database. I&#39;ve already tried:

**Database context class:**

    modelBuilder.Entity&lt;Parent&gt;()
                .HasMany(p =&gt; p.Children)
                .WithOptional()
                .WillCascadeOnDelete(true);

this works fine, but I still have redundant records in database with `Parent_Id = null` fields when I do 

    parent.Children.Clear();
    repository.InsertOrUpdate(parent);

 in my repository class. Also the same behavior is when I do:

    modelBuilder.Entity&lt;Parent&gt;()
                .HasMany(pr =&gt; pr.Children)
                .WithOptional(ri =&gt; ri.Parent)
                .WillCascadeOnDelete(true);

with additional `Parent` property in `Child` class

    public class Child
    {
        ...
        public Parent Parent { get; set; }
        ...
    }

or when I do

    modelBuilder.Entity&lt;Child&gt;()
                .HasOptional(p =&gt; p.Parent)
                .WithMany(p =&gt; p.Children)
                .HasForeignKey(p =&gt; p.Parent_Id)
                .WillCascadeOnDelete(true);


with additional Parent_Id property in `Child` class

    public class Child
    {
         ...
         public int Parent_Id { get; set; }
         ...
    }
        

**So, how can I configure cascade deleting correctly? Or how should I supposed to remove those child entities? I assume this is casual task but I&#39;m just missing something.**

How to remove child one to many related records in EF code first database?

I&#39;m wondering why there is no Detach method on the DbContext object like there is for ObjectContext. &#160;I can only assume this omission was intentional, but I have a hard time figuring out why. &#160;I need to be able to detach and re-attach entities (for putting in the cache in an ASP.NET project, for example). &#160;However, since I can&#39;t detach an entity, when I try to attach an entity that was associated with a previous context, I get the &quot;An entity object cannot be referenced by multiple instances of IEntityChangeTracker&quot; exception.

What&#39;s the guidance here? &#160;Am I missing something?


Entity Framework Code First - No Detach() method on DbContext

The database is created successfully (as are the tables) but is not seeded. I have spent several hours and read tons of articles but have not been able to get it. Any suggestions?

On a side note, is it possible to call the initializer without having a reference to my DatabaseContext in the client?

I have included all the relevant code I could think of. If anything else would be helpful, please let me know.

Things I&#39;ve Tried:

1. I deleted my connection string (since it defaults to sqlexpress anyways, just the name changed)
2. I changed DropCreateDatabaseIfModelChanges to DropCreateDatabaseAlways, still the same.

Edit: The really weird thing is it worked once, but I have no idea how or why it broke again. I am assuming connection strings, but who knows.

DatabaseInitializer.cs

    public class DatabaseInitializer : DropCreateDatabaseIfModelChanges&lt;DatabaseContext&gt;
    {
      protected override void Seed(DatabaseContext context)
      {
        // Seeding data here
        context.SaveChanges();
      }
    }

DatabaseContext.cs

    public class DatabaseContext : DbContext
    {
      protected override void OnModelCreating(DbModelBuilder mb)
      {
        // Random mapping code
      }

      public DbSet&lt;Entity1&gt; Entities1 { get; set; }
      public DbSet&lt;Entity2&gt; Entities2 { get; set; }

    }
    
Global.asax.cs - Application_Start()

    protected void Application_Start()
    {
      Database.SetInitializer&lt;DatabaseContext&gt;(new DatabaseInitializer());
      AreaRegistration.RegisterAllAreas();
      RegisterGlobalFilters(GlobalFilters.Filters);
      RegisterRoutes(RouteTable.Routes);
    }

Client web.config

    &lt;connectionStrings&gt;
      &lt;add name=&quot;DatabaseContext&quot; connectionString=&quot;data source=.\SQLEXPRESS;Database=Database;Integrated Security=SSPI;&quot; providerName=&quot;System.Data.SqlClient&quot; /&gt;
    &lt;/connectionStrings&gt;

#SOLUTION#

For the sake of documentation, I am sharing my solution here. Navigating all the comments would be a pain anyways. In the end I had DatabaseInitializer and DatabaseContext in separate classes. I don&#39;t really understand while these tiny changes fixed it, but here it is.

DatabaseInitializer.cs

    public class DatabaseInitializer : CreateDatabaseIfNotExists&lt;DatabaseContext&gt;
    {
      protected override void Seed(DatabaseContext context)
      {
        // Seed code here
      }
    }

DatabaseContext.cs

    public class DatabaseContext : DbContext
    {
      public DatabaseContext() : base(&quot;MyDatabase&quot;) { }

      protected override void OnModelCreating(DbModelBuilder mb)
      {
        // Code here
      }
      
      public DbSet&lt;Entity&gt; Entities { get; set; }
      // Other DbSets
    }

Global.asax.cs - Application_Start()

    protected void Application_Start()
    {
      Database.SetInitializer(new DatabaseInitializer());
      AreaRegistration.RegisterAllAreas();
      RegisterGlobalFilters(GlobalFilters.Filters);
      RegisterRoutes(RouteTable.Routes);
    }

    

How can I get my database to seed using Entity Framework CodeFirst?

Entity Framework Code First will auto-create a table in the database base based on the Model.

Is there an attribute that will avoid this?

How to ignore a property when using Entity Framework Code First

Started to use the add-migration command in the package manager console to generate the migrations for my model. My question is, the up and down method. I assume that the purpose of the down method is to remove all dependencies and drop the tables if they are already in the database? Also that the down method will be executed before the up method?
The up method is then the reverse, create/update tables/indexes etc?

Sometimes when i use this then the down method gets a lot of create tables that then are dropped? Recently it created and dropped a lot of tables and almost the same thing happened in the up method. Why?

C# Code-First migration, up/down?

[My previous question][1] made me think again about layers, repository, dependency injection and architectural stuff like this.  

My architecture now looks like this:  
I am using EF code first, so I just made POCO classes, and context. That creates db and model.  
Level higher are business layer classes (Providers). I am using different provider for each domain... like MemberProvider, RoleProvider, TaskProvider etc. and I am making new instance of my DbContext in each of these providers.  
Then I instantiate these providers in my controllers, get data and send them to Views.


My initial architecture included repository, which I got rid of because I was told that it just adds complexity, so why I don&#39;t just use EF only. I wanted to did that.. working with EF directly from controllers, but I have to write tests and it was a bit complicate with real database. I had to fake - mock data somehow. So I made an interface for each provider and made fake providers with hardcoded data in lists. And with this I got back to something, where I am not sure how to proceed correctly.

These things starts to be overcomplicated too quickly... many approaches and &quot;pattterns&quot;... it creates just too much noise and useless code.

**Is there any SIMPLE and testable architecture for creating and ASP.NET MVC3 application with Entity Framework?**


  [1]: https://stackoverflow.com/q/5609473/671686

ASP.NET MVC3 and Entity Framework Code first architecture

I created a new Entity Frameworks Code First app and the DbSet (People) is returning null.

    public class Person
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
        
    public class Repository : DbContext
    {
        public DbSet&lt;Person&gt; People;
    }

**web.config**: connection string  

    &lt;connectionStrings&gt;
      &lt;add name=&quot;Repository&quot;
           connectionString=&quot;Data Source=|DataDirectory|Repository.sdf&quot;
           providerName=&quot;System.Data.SqlServerCe.4.0&quot;/&gt;
    &lt;/connectionStrings&gt;

Now when I call 

    Repository _repo = new Repository()
    _repo.People;

`_repo.People` will be null



What I am missing?

 - Microsoft.Data.Entity.Ctp.dll is
   referenced
 - I have tried with and
   without a database initializer.



Why is my DbContext DbSet null?

I have an MVC3 and EF 4 Code First application, which is configured to change the DB when the model changes, by setting the DB Initializer to a `DropCreateDatabaseIfModelChanges&lt;TocratesDb&gt;`, where `TocratesDb` is my derived `DbContext`.

I have now made a change to the model, by adding properties to a class, but when EF tries to drop and recreate the DB, I get the following error:

    Cannot drop database &quot;Tocrates&quot; because it is currently in use.

I have absolutely no other connections anywhere open on this database.  I assume that my cDbContext still has an open connection to the database, but what can I do about this?

**NEW:** Now my problem is how to re-create the database based on the model.  By using the more general IDatabaseInitializer, I lose that and have to implement it myself.  

Database in use error with Entity Framework 4 Code First

I&#39;ve got multiple classes (including TPT) in my project. Each POCO has a `BaseClass`, which has a `GUID` (called `GlobalKey`) as primary key.

First I used `DataAnnotations` to create correct foreign keys. But then I&#39;ve got problems synchronizing the corresponding GUID with the object itself.

Now I want to have only one virtual navigation property so that the GUID field in the database is created by `NamingConvention`. But the field name always adds an underscore followed by the word `GlobalKey` (which is right). When I want to remove the underscore, I don&#39;t want to go thru all my POCOs in the fluent API to do this:

    // Remove underscore from Navigation-Field     
    modelBuilder.Entity&lt;Person&gt;()
                .HasOptional(x =&gt; x.Address)
                .WithMany()
                .Map(a =&gt; a.MapKey(&quot;AddressGlobalKey&quot;));

Any ideas to do this for all POCOS by overwriting a convention?

Thanks in advance.

Andreas


All Code First Solutions on Gang of Coders

Total of 25 Code First Solutions

Why use ICollection and not IEnumerable or List<T> on many-many/one-many relationships?