Entity Framework won't detect changes of navigation properties

c#, entity-framework-4

Solution

First of all: You MUST follow @billy's advice to use `Include`. Your remark "p.Address IS NOT NULL!" is only true because you are watching `p.Address` in the debugger and thereby triggering lazy loading in the debugger, so the change of setting the address to `null` is detected. In release mode or when you don't inspect the properties in the debugger your code wouldn't work and no changes would be saved.

So, the answer to your Edit 3 is: No.

Second: `var entry = ctx.Entry(p)` only returns entity states and you didn't change an entity state but instead a relationship state, or more precisely you deleted a relationship. You can't inspect relationship states with the `DbContext` API but only with the `ObjectContext` API:

Person p = ctx.People.Include(x => x.Address).First();
p.Address = null;
var objCtx = ((IObjectContextAdapter)ctx).ObjectContext;
var objentr = objCtx.ObjectStateManager.GetObjectStateEntries(EntityState.Deleted);

`objentr` will have an entry of type `RelationshipEntry` now:

EF will consider this relationship entry together with entity state entries when you call `SaveChanges()` and delete the relationship, i.e. set the `Address` foreign key column of the `Person` in the database to `NULL`.

About Edit 2: Changing a foreign key property (which is a scalar property in your model) is a change of the entity itself, so the entity state will be `Modified` in this case.

Problem

I'm having trouble with detecting changes of a navigation property: My testing model looks like this: ``` public class Person { public int Id { get; set; } public string Name { get; set; } public virtual Address Address { get; set; } } public class Address { public int Id { get; set; } public string Name { get; set; } } ``` I've created and saved an object of type `Person` with both `Name` and `Address` properties assigned. My problem is that if I fetch the `Person` object back from the database and I change the `Address` property (ex. to null) then EF doesn't detect the change! My code is this: ``` using (var ctx = new EFContext()) { Person p = ctx.People.First(); // p.Address IS NOT NULL! p.Address = null; var entry = ctx.Entry(p); } ``` Why is `entry.State` `Unchanged` ? Edit: If I call `SaveChanges`, the record is saved correctly (the `Address` become null)! Edit 2: I've created the foreign key property as billy suggested. If I inspect the `Person` object in Visual Studio, the `State` is `Modified`. If I don't stop with the debugger inspecting the object's values, the state is `Unchanged`! Edit 3: Loading the `Person` object using `ctx.People.Include(x => x.Address).First();` solves the problem. Is there a way to avoid calling `Include` and continue to modify the `Address` property instead of the `AddressId` one?

Original source