Question

我有一个内存列表和来自MySQL的对象

requiredUserNames：调用 “其中users.Contains（us.Username）” ，为什么它不区分大小写包含用户是内存列表对象（普通c＃对象）而第二个代码正常工作，因为C＃区分大小写：

var users = (from u in _dbContext.MyUser
             select new 
             {
                 UserName = u.UserName
             }).ToList();

var requiredUserNames = (from us in _dbContext.NextUsers
                    // users is a memory list and not a database list why executed as case insensitive
                   where users.Contains(us.Username)
                   select new { Username = us.Username}).ToList();


var requiredUserNames02 = (from us in _dbContext.NextUsers
                        // here working normally as case sensitive
                     where users.FindIndex((usr) => usr.Username.Equals(us.Username)) > -1
                   select new { Username = us.Username }).ToList();

Answer 1

users是本地列表，这是正确的。但是_dbContext.NextUsers是远程的，您正在询问MySQL实例，例如：

select us.* from NextUsers us where us.UserName in ('theNameFromLocalList','...')

IOW是MySQL执行不敏感的搜索。如果您避免这种情况，那么这样做的成本会更高，但是：

var requiredUserNames = (from us in _dbContext.NextUsers.AsEnumerable()
                    // users is a memory list and not a database list why executed as case insensitive
                   where users.Contains(us.Username)
                   select new { Username = us.Username}).ToList();

为什么内存列表包含不区分大小写的代码？

1 个答案: