Entity Framework won't persist data in SQL Express (MDF)

Question

Hi guyz, I'm going crazy abou this, because I can't see what I'm doing wrong!!! Please help me!!!

I was developing a application using Entity Framework and storing data in a .mdf database, my code can read the data, apparently it can save too, but only apparently. I get no erros, while the program is running it act like the data was saved, I can for example save an object, dispose the context, create a new one, and then when I search my object he is there!!! But when I query the database to see the stored data there's nothing there!!! If I close the app and run it again, all data was gone! Here's a example code I wrote just to test:

        using (DatabaseEntities e = new DatabaseEntities())
        {
            for (int i = 0; i < 50; i++)
            {
                User u = new User();
                u.Nome = "User" + i.ToString();
                e.AddToUser(u);
            }
            int c = e.SaveChanges(true);

            List<User> us = e.User.Where<User>(x => x.ID < 50).ToList<User>();

            foreach (User u in us)
                Console.WriteLine("ID: " + u.ID + " Hello from " + u.Nome);

            Console.ReadKey();
        }

When I run this, I get the 50 outputs, if I look the content of the c variable in the debug, there's 50 changes, everythings seems to be fine, but when I start my query browser and look in the content of my MDF database, there's nothing there!!!

Probably it's something very simple but I can't see what it is, I need your help guyz!

Answer 1

A few things leap to mind:

• double/treble-check your connection string; are you really talking to the file that you think you are?
• are you using transactions anywhere and not committing them?
• do you have the mdf file set to "Copy Always" (or whatever it is).... i.e. are you constantly overwriting the mdf whenever you hit build/play?

Also - I don't think it'll matter in this case, but to verify data you should use a different entities/data-context:

using (DatabaseEntities e = new DatabaseEntities()) {
    for (int i = 0; i < 50; i++) {
        User u = new User();
        u.Nome = "User" + i.ToString();
        e.AddToUser(u);
    }
    int c = e.SaveChanges(true);
}
using (DatabaseEntities e = new DatabaseEntities()) {
    List<User> us = e.User.Where<User>(x => x.ID < 50).ToList<User>();
    foreach (User u in us)
        Console.WriteLine("ID: " + u.ID + " Hello from " + u.Nome);
}
Console.ReadKey();

Like I said - I doubt it'll matter here, but worth checking...

Answer 2

What's the type of ID ? A GUID? How do you set the ID? With NewID() as default? If that's the case, an O/R mapper can't read the ID back and will likely flag the entity as wrongly saved. Also check with SQL Profiler if you get any queries executed on the db.

Answer 3

Hi guyz, i'll check your tips when I get in home later, thankz a lot for answering!

Marc, yes, I'm talking with the correct .mdf, I know this because I added some data manually in the database, and then I've made a query to check if I could read the new data and I can! I'm not using transactions, my code is pretty simple, almost like what I've posted here.

Frans, the ID is a bigint in the database. When I create an object I don't set this ID, I just create it with a User user = new User(), then I set the properties and save it! It always worked for me!

aleemb, it step through, and like I said, if I close the context and open it again, the data is there. I can for example dispose the context, dispose my user class, then I search the user again in a new context and it find it, with all properties set correctly! I'm guessing it can be a connection string like you said, but the connection string is the default created by the visual studio, then I think it can be some parameter like Marc said! I really don't know. I've googled and didn't found anything like, so maybe it's a very stupid thing I'm doing wrong, a little detail, I don't know.

Thankz for the help! I'll make some tests in some hours.

Answer 4

Guyz, I just found what was going wrong, and I guess there's nothing wrong actually. I forced an error, and then I could see the database that I was accessing was in the bin directory, the Visual Studio copied my database to the bin directory everytime I run the app, so that's why if I add some data manually I could see it, but the saves in the runtime aren't persisted. I always worked with database in servers, it's my first time with local databases, so I messed up it, but thankz a lot for the help!