I am working on windows form based application. I'm working with Entity Framework 6.0 on Visual Stduio 2012. I implemented some windows forms of course.For now i have only 1 master detailed form. Here is screen of that master detailed form 
First of all i give more detail about my project. As u can see on the left side of print screen there are names like Depolar,Siparisler,SiparislerDetay... In SiparisGirisiForm field like SiparisNo,Siparis Tarihi,... are coming from Siparisler in SampleDataSet. I took these fields from Siparisler that exist in SampleDataSet. And for my Siparisler's detail, i choose SiparislerDetay in Siparisler and SiparislerDetay is GridControl. To here everything is ok when i run my program and open SiparisGirisiForm i entered some values and clicked to Kaydet barMenuButton(This button makes save to database basically) on the top left side of the screen i am getting this error: column of Siparis_Id doesn't allow null values.
In database and EntityModel structure its definetly true. I must not save a detail info without any relation with its master. column Siparis_Id is foreign key in SiparislerDetay class and related Siparisler's Id column. I cant save this values to database. For 2 days i am counting on my place. My project doesn't move on. I must solve this problem. Is there anyone to help to this one? Thanks...
Set entity framework code generation strategy from None to Default, on model designer screen. And you see, it works.