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Asked: 2026-06-05T11:27:15+00:00

I’m very new to this Entity Framework Object Services Overview (Entity Framework) , so

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I’m very new to this Entity Framework Object Services Overview (Entity Framework), so forgive me if I use the wrong terminology here.

I’m using the EDMX file to connect to an SQLite database. What I’m trying to do is use the ObjectSet<T> normally, to access a collection of objects from a table in the database. However, I want to additionally store some run-time-only data in the objects in that set. In my case, I have a set of devices stored in the database, but upon startup, I want to mark them as “Connected” or “Disconnected”, and keep track of this state throughout execution.

Since the (row) types generated by the EDMX are partial I’ve added another partial definition, and added my public bool Connected property there. This seems to work, I can set it, and future queries provide objects with the same value that I previously set. The problem is, I don’t know a) how it is working, or b) whether I can trust it. These doubts come from the fact that these aren’t really collections of objects we’re dealing with, right?

Hopefully that made sense, else I can provide more detail.

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1 Answer

  1. Editorial Team

    What you’re doing is completely safe.

    ObjectSet is still a collection of objects. With a lot magic added underneath.
    I am not an expert on the internals but here is how I think it works:

    The Entity Framework has a StateTracker hat keeps track of all the entities you’re working with.

    Every class in your EDMX model is required to have a key. EF is using that key internally so that it loads that specific object only once into memory.

    var foo = db.Foos.Single(x => x.Id == 1); // foo with Id 1 is unique (in memory)
var foo2 = db.Foos.Single(x => x.Id == 1); // same instance of foo, but with updated values
var foo3 = db.Foos.Single(x => x.Id == 2) // a new unique instance (Id = 2)

bool sameObject = Object.Equals(foo, foo2); // will return true;

    At every select the following happens:

    Is an instance of class Foo already tracked/does it already exist?

    Yes -> update the properties of the existing instance from the database.
    No -> create new instance of class Foo (take values from database)

    Of course it can only ever update mapped properties. So the ones you defined in the partial class won’t be overwritten.

    In case you’re going to use code first. There is also the [NotMapped] attribute, that makes sure that the property won’t be included in the table if you generate a new database from your code first models.

    I hope I could clarify some things for you.

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