Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
200 views
in Technique[技术] by (71.8m points)

c# - Convert string to datetime value in LINQ

Suppose I have a table storing a list of datetime (yyyyMMdd) in String format. How could I extract them and convert them into DateTime format dd/MM/yyyy ?

e.g. 20120101 -> 01/01/2012

I have tried the following:

var query = from tb in db.tb1 select new { dtNew = DateTime.ParseExact(tb.dt, "dd/MM/yyyy", null); };

But it turns out the error saying that the ParseExact function cannot be recgonized.

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

It's probably worth just doing the parsing locally instead of in the database, via AsEnumerable:

var query = db.tb1.Select(tb => tb.dt)
                  .AsEnumerable() // Do the rest of the processing locally
                  .Select(x => DateTime.ParseExact(x, "yyyyMMdd",
                                                CultureInfo.InvariantCulture));

The initial select is to ensure that only the relevant column is fetched, rather than the whole entity (only for most of it to be discarded). I've also avoided using an anonymous type as there seems to be no point to it here.

Note how I've specified the invariant culture by the way - you almost certainly don't want to just use the current culture. And I've changed the pattern used for parsing, as it sounds like your source data is in yyyyMMdd format.

Of course, if at all possible you should change the database schema to store date values in a date-based column, rather than as text.


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...