How do I convert ContainsKey to TryGetValue

Question

Im trying to figure out to convert the following statement to a trygetvalue.

Any help would be greatly appreciated.

filters.ContainsKey("companyCode") ? filters["companyCode"] : string.Empty;

I have code that I inherited that has about 25 of these that builds one query statement.

@PatrickHofman Seems like micro-optimization, but I'll take your word for it. — Heretic Monkey, Mar 20 '18 at 15:54
What is faster? Walking a dictionary twice or once, the answer is easy. How it affects performance depends on the number of calls. @MikeMcCaughan — Patrick Hofman, Mar 20 '18 at 15:55
Im trying to do it for a performance gain. This gets called a good bit by our customers. Also, also there 25 just like it. — jeffkenn, Mar 20 '18 at 16:01
@PatrickHofman Sure. I'm not disagreeing with you, and I think your answer is helpful. But there are costs and risks to these kinds of refactors, right? — Heretic Monkey, Mar 20 '18 at 16:10
@DanWilson Getting the value by index calls `FindEntry()` again, whereas `TryGetValue` does not. Check out [this answer](https://stackoverflow.com/questions/9382681/what-is-more-efficient-dictionary-trygetvalue-or-containskeyitem) — Rufus L, Mar 20 '18 at 16:13

score 6 · Answer 1 · answered Mar 20 '18 at 15:46

6

You have to create an if statement where you assign the default in case the filter wasn't found:

For C# 7:

if (!filters.TryGetValue("companyCode", out string value))
    value = string.Empty;

And pre-C# 7:

string value;

if (!filters.TryGetValue("companyCode", out value))
    value = string.Empty;

answered Mar 20 '18 at 15:46

Patrick Hofman

Thanks so much. I just couldn't see it. – jeffkenn Mar 20 '18 at 15:50
Why an `if` statement and not a ternary? – maccettura Mar 20 '18 at 15:51
Because for beginner programmers this code is clearer. Functionally it wouldn't matter which to pick @maccettura. – Patrick Hofman Mar 20 '18 at 15:52
@maccettura What code would be in the `true` block of a ternary operation where `TryGetValue` is the condition? Seems like a redundant assignment would have to happen. – Rufus L Mar 20 '18 at 16:05
1

@RufusL See Tim's answer: `string result = filters.TryGetValue("companyCode", out string code) ? code : string.Empty;` – maccettura Mar 20 '18 at 16:09
@maccettura Yeah, sorry, I meant why would that be better? You have an additional assignment operation in the `true` case. Just curious. – Rufus L Mar 20 '18 at 16:09
1

@RufusL I wouldnt say a ternary is better, I just personally thought it was cleaner. You have a solid point about the extra assignment though. – maccettura Mar 20 '18 at 16:11

score 4 · Answer 2 · answered Mar 20 '18 at 15:46

4

With C#7 you can use this one liner:

string result = filters.TryGetValue("companyCode", out string code) ? code : string.Empty;

If you can't use inline out variables you need two lines:

string code;
string result = filters.TryGetValue("companyCode", out code) ? code : string.Empty;

answered Mar 20 '18 at 15:46

Tim Schmelter

2 Answers2