public void TestEntityState()
{
using (var context = new MyDBContext())
{
//获取最后一条记录
//由于EF不支持Last()查询，因此，先对其进行降序排列，然后取第一条记录
var client = (from c in context.OrderClients
orderby c.ClientID descending
select c).FirstOrDefault();
if (client != null)
{
DbEntityEntry <OrderClient> clientEntry = context.Entry <OrderClient>(client);
Console.WriteLine("\n修改属性前：状态={0}", clientEntry.State);
Assert.IsTrue(clientEntry.State == EntityState.Unchanged);
OrderClientHelper.PrintEntityPropertyValue(clientEntry, "PostCode");
//把邮编当成数字，加1，作为修改后的新值进行测试
int newPostCode = Int32.Parse(client.PostCode) + 1;
client.PostCode = newPostCode.ToString();
context.ChangeTracker.DetectChanges();
Console.WriteLine("\n修改属性后：状态={0}", clientEntry.State);
Assert.IsTrue(clientEntry.State == EntityState.Modified);
OrderClientHelper.PrintEntityPropertyValue(clientEntry, "PostCode");
int result = context.SaveChanges();
Assert.IsTrue(result == 1);
Console.WriteLine("\n保存到数据库后：状态={0}", clientEntry.State);
OrderClientHelper.PrintEntityPropertyValue(clientEntry, "PostCode");
}
}
}
