c# 4.0 - Error using foreign keys in entity framework -

i used foreign key

after clicked delete button

runs messagebox.show("error");

because foreign key

after clicked delete button

i not want insert table

again gives same error, delete

never can not insert or update table

again gives same error, delete

how problem solved

code delete

private void button1_click(object sender, eventargs e)     {         try         {             int del = convert.toint32(datagridview1.rows[datagridview1.currentrow.index].cells[0].value);              t1 query = (from p in db.t1 p.id == del select p).firstordefault();              db.t1.remove(query);             db.savechanges();             fill();         }         catch         {              messagebox.show("error");         }      } 

code insert

try         {               db.t1.add(new t1()                 {                     names=textbox1.text                 });             db.savechanges();             //fill();         }         catch         {              messagebox.show("error");         } 

class code first

public partial class t1 {     public t1()     {         this.t2 = new list<t2>();     }      public int id { get; set; }     public string names { get; set; }     public virtual icollection<t2> t2 { get; set; } }  public partial class t2 {     public int id { get; set; }     public nullable<int> fname { get; set; }     public virtual t1 t1 { get; set; } } 

sql setup http://sarbandi.ir/keramati/sqlpackage.exe

code example http://sarbandi.ir/keramati/examample.rar

i assume t1 object try delete has t2 objects in collection (as i used foreign key). first problem, delete, solved by

t1 t1 = db.t1.firstordefault(p => p.id == del);    // same code, other syntax, or: db.t1.find(del);  foreach(var t2 in t1.t2.tolist()) {     db.t2.remove(t2); } db.t1.remove(t1);  db.savechanges(); 

the second error caused fact have 1 dbcontext instance (db). second time try save, db second effort commit delete failed before, that's still in there. (if you'd catch exception in stead of swallowing confirm this). delete , insert actions should each use own context instance new in using construct:

using(var db = new mycontext()) {     // stuff. } 

side notes:

• try separate ui , data logic if meant more exercise.
• catch exceptions: catch(exception exception) in stead of showing messagebox.

(i must admit didn't @ links, hope bring in right track).