在符合特定条件的表中查找最新记录

Question

I am using C# and T-SQL.

I am trying to get the date of the most recent record from a table matching a specific condition, and I am stuck on the matching part. Currently what I have is:

date = (DateTime)(context.corresps.OrderByDescending(x => x.tevent).Select(x => x.tevent).FirstOrDefault());

What I am not able to figure out how to add to this statement is:

WHERE cmethod = 'W'

I could rewrite this as a standard LINQ query, but am trying to better myself. Thank you for any assistance.

Answer 1

除非我遗漏了什么：

var date = context.corresps.OrderByDescending(x => x.tevent) .Where(x => x.cMethod == "W") .Select(x => x.tevent) .FirstOrDefault());

Answer 2

I think you misunderstood the whole concept.

when you have

context.corresps.OrderByDescending(x => x.tevent).FirstOrDefault()

you get a corresp that has the highest value for the field tevent

you can add a condition to your query by using where clause like this

context.corresps.Where(x => x.cmethod = 'W').OrderByDescending(x => x.tevent).FirstOrDefault()

and at the end you can not cast your corresp to DateTime unless you have implemented this feature inside corresp class. so you should get a date time you want from the object itself. final code is going to be something like this

var lastCorresp = context.corresps.Where(x => x.cmethod = 'W').OrderByDescending(x => x.tevent).Select(x => x.tevent).FirstOrDefault();
var lastDate = lastCorresp.tevent; //or any other field that represents the date time you want, since you've ordered your query by tevent field I assume that this field holds the date time you want to use