c# - sqlexception cannot insert duplicate key row -

tried alter sql statement change format of how user names create. creating dummy data testing on webpage need multiple users. want change name user student{integer}@email.com , wanted change name student{integer}

error

sqlexception: cannot insert duplicate key row in object 'dbo.users' unique index 'ux_users'. duplicate key value (1, student0@email.com). statement has been terminated.

sql statement

string basestring = "student{0}@email.com"; string username = "student{0}";  using (database dc = new database()) {     dc.connection.open();     (int = 0; < 400; i++)     {         string email = string.format(basestring,i);         string sname = string.format(username, i);         user u = new user(){ name = sname, username = email, institutionuniqueid = email, email = email, creationdate=datetime.now, institutionsid=1, guid= guid.newguid() };         dc.users.insertonsubmit(u);      }     dc.submitchanges(system.data.linq.conflictmode.failonfirstconflict); } 

this getting error:

dc.submitchanges(system.data.linq.conflictmode.failonfirstconflict); 

i using linqpad test out.

change code this:

string basestring = "student{0}@email.com"; string username = "student{0}";  using (database dc = new database()) {      (int = 0; < 400; i++)     {          dc.connection.open();         string email = string.format(basestring,i);         string sname = string.format(username, i);         user u = new user(){ name = sname, username = email, institutionuniqueid = email, email = email, creationdate=datetime.now, institutionsid=1, guid= guid.newguid() };         dc.users.insertonsubmit(u);          dc.submitchanges(system.data.linq.conflictmode.failonfirstconflict);         dc.connection.close();     }  } 

you need place submit changes inside loop

best regards