C# Finding the maximum value of a string with linq

问题

This is what I have and it keeps returning null.

It doesn't recognize the Convert.toInt32 when I add a where statement

var maxTopID = (from max in dbcontext.Topics.Local
               select max.TopicID).Max();

回答1:

How about converting the TopicID in SELECT and use String.IsNullOrEmpty() to remove empty string, like:

 var maxTopID = (from max in dbcontext.Topics.Local
                 where !String.IsNullOrEmpty(max.TopicID)
                 select Convert.ToInt32(max.TopicID)).Max();

See the Demo

回答2:

I think you are saying that TopicID is string and you want to convert it to int

var list= (from max in dbcontext.Topics.Local
                     where  max.TopicId != null
                     select max.TopicID).ToList();

int max=0;

if (list.Count() !=0)
max=list.Select(int.Parse).ToList().Max();

max will contain max value from list which is converted to list of integer

回答3:

Check for the null condition as mentioned in below query

var maxTopID = (from max in dbcontext.Topics.Local
                 where  max.TopicId != null
                 select max.TopicID).Max();

来源：https://stackoverflow.com/questions/20392753/c-sharp-finding-the-maximum-value-of-a-string-with-linq