问题描述
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我有一个表达式,在多个LINQ查询中使用了几次,因此我将其分离为返回表达式的自己的方法。该函数的lambda部分看起来有些凌乱。任何人都想破解它,使其更具可读性和/或更小?
private Expression<Func<Message,bool>> UserSelector(string username,bool sent)
{
return x => ((sent ? x.FromUser : x.ToUser).Username.ToLower() == username.ToLower()) && (sent ? !x.SenderDeleted : !x.RecipientDeleted);
}
关于它的作用的快速英文描述是检查布尔值sent
并基于该布尔值检查Message.FromUser
或Message.ToUser
。
如果用户正在查看他/她的发件箱,则sent
为真,它将查看x.FromUser.Username == username
和x.SenderDeleted == false
。
如果用户正在查看他/她的收件箱,则它执行相同的逻辑,但发送为false,而是检查x.ToUser
和x.RecipientDeleted
。
也许这是最简单的方法,但是我愿意进行一些重构。
答案编辑
我真的很喜欢Davy8的答案,但我决定更进一步,用两个表达式代替一个带有嵌套函数的表达式。现在,我有以下方法:
/// <summary>
/// Expression to determine if a message belongs to a user.
/// </summary>
/// <param name=\"username\">The name of the user.</param>
/// <param name=\"sent\">True if retrieving sent messages.</param>
/// <returns>An expression to be used in a LINQ query.</returns>
private Expression<Func<Message,bool>> MessageBelongsToUser(string username,bool sent)
{
return x => (sent ? x.FromUser : x.ToUser).Username.Equals(username,StringComparison.OrdinalIgnoreCase);
}
/// <summary>
/// Expression to determine if a message has been deleted by the user.
/// </summary>
/// <param name=\"username\">The name of the user.</param>
/// <param name=\"sent\">True if retrieving sent messages.</param>
/// <returns>An expression to be used in a LINQ query.</returns>
private Expression<Func<Message,bool>> UserDidNotDeleteMessage(string username,bool sent)
{
return x => sent ? !x.SenderDeleted : !x.RecipientDeleted;
}
所以现在我的查询看起来像这样:
/// <summary>
/// Retrieves a list of messages from the data context for a user.
/// </summary>
/// <param name=\"username\">The name of the user.</param>
/// <param name=\"page\">The page number.</param>
/// <param name=\"itemsPerPage\">The number of items to display per page.</param>
/// <param name=\"sent\">True if retrieving sent messages.</param>
/// <returns>An enumerable list of messages.</returns>
public IEnumerable<Message> GetMessagesBy_Username(string username,int page,int itemsPerPage,bool sent)
{
var query = _dataContext.Messages
.Where(MessageBelongsToUser(username,sent))
.Where(UserDidNotDeleteMessage(username,sent))
.OrderByDescending(x => x.SentDate)
.Skip(itemsPerPage * (page - 1))
.Take(itemsPerPage);
return query;
}
/// <summary>
/// Retrieves the total number of messages for the user.
/// </summary>
/// <param name=\"username\">The name of the user.</param>
/// <param name=\"sent\">True if retrieving the number of messages sent.</param>
/// <returns>The total number of messages.</returns>
public int GetMessageCountBy_Username(string username,sent))
.Count();
return query;
}
我要说的是一些非常易于阅读的英语查询,谢谢大家!
参考:http://www.codetunnel.com/blog/post/64/how-to-simplify-complex-linq-expressions
解决方法
将其拆分为一个单独的函数:
private Expression<Func<Message,bool>> UserSelector(string username,bool sent)
{
return message=> InnerFunc(message,username,sent);
}
private static bool InnerFunc(Message message,string username,bool sent)
{
if(sent)
{
return string.Equals(message.FromUser.Username,StringComparison.InvariantCultureIgnoreCase) && !message.SenderDeleted;
}
return string.Equals(message.ToUser.Username,StringComparison.InvariantCultureIgnoreCase) && !message.RecipientDeleted;
}
或者,可以内联它以保持闭包用法:
private Expression<Func<Message,bool sent)
{
Func<Message,bool> innerFunc = message =>
{
if (sent)
{
return string.Equals(message.FromUser.Username,StringComparison.InvariantCultureIgnoreCase) &&
!message.SenderDeleted;
}
return string.Equals(message.ToUser.Username,StringComparison.InvariantCultureIgnoreCase) &&
!message.RecipientDeleted;
};
return message => innerFunc(message);
}
(经编辑可将ѭ13culture和ѭ14cases用于具有不同区域性设置的奇怪边缘情况。)
,你有剃须刀吗?很多时候,我会像这样写一些foreach循环,看看Resharper是否可以重构它。尽管可以评估所提出的任何解决方案的性能,但我认为可读性是最重要的。
,只要您将为该问题写的描述作为评论,它就会帮助尝试阅读/理解它的人正确吗?