Database operation expected to affect 1 row(s) but actually affected 0 row(s)

_dbcontext.Update(q);
_dbcontext.SaveChanges();

当保存数据时提示错误，原因是没有获取到主键id值

Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded

asp.net  更新数据时报错：Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded

原因：Check your object, does it pass Primary Key Null. This Exception is Generally due this reason only.

对象的主键为空，导致不能更新，检查你要更新的对象，查看主键是否为空，或0