CODEWITHSUNDEEP
c#entitydbcontext
Makalele
Makalele

Reputation: 7521

How to generate usable dbcontext from database using entity framework?

I've made simple database with 2 tables and few columns in each. In some tutorial I read when I install entity framework 4.1+ I can generate "DbContext code" and then I can use Local context to get ObservableCollection, which is better than DbSet, because it's automatically updating UI. So I installed entity framework 4.1, selected my database model and chose "ADO.NET DbContext Generator". So I got this:

namespace BazaStudentow
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;

    public partial class DatabaseEntities : DbContext
    {
        public DatabaseEntities()
            : base("name=DatabaseEntities")
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }

        public DbSet<Notes> Notes { get; set; }
        public DbSet<Students> Students { get; set; }
    }
}

plus StudModel.tt file with simple table models.

So in main class I added this: DatabaseEntities db = new DatabaseEntities();

But then I realized that db.Students.Local is empty (I manually added 2 records in editor before), although db.Students has 2 records. So I found this: ObservableCollection better than ObjectSet (second answer), but there's no such method "Load". What am I missing? Should I add some special code to get this "Load" working?

I just simple wanted to: 1. Make new project and add simple database. 2. Automatically generate some code using Entity Framework so I can just bind table to DataGrid or something, which is automatically updated when data is changed (so I need ObservableCollection). 3. When I have this add some functions to Insert/Update/Delete data (with autoupdate ofc).

Please help, cheers ;)

Upvotes: 1

Views: 1930

Answers (1)

whistle britches
whistle britches

Reputation: 127

There will be nothing in Local until you execute a query against the database. One way to accomplish this is to call Load, which does so, and returns an ObservableCollection(Of Student) (in your case).

Dim bs = New BindingSource
Dim s = db.Students

s.Load()

'At this point, Local will contain all students.
'Cast to a BindingList, which stays in sync with the ObservableCollection.

bs.DataSource = s.Local.ToBindingList

Or I guess you can go this route:

Dim bs = New BindingSource
db.Students.Load
bs.DataSource = db.Students.Local.ToBindingList

Sorry, C# is not my friend. The above code should convert easily.

The steps you took above to generate the model and context look fine.

Upvotes: 1

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