C
C#13mo ago
Sonath

✅ Recommended way to handle null results from a repository GET action?

I'm learning .NET Core and in Java (yes, I did Java) I used to create custom exceptions to throw. The equivalent would be
var company = _repository.Company.GetCompany(companyId, trackChanges);
if (company is null)
throw new CompanyNotFoundException(companyId);
var company = _repository.Company.GetCompany(companyId, trackChanges);
if (company is null)
throw new CompanyNotFoundException(companyId);
Is this a good idea?
20 Replies
Pobiega
Pobiega13mo ago
Generally, no this is using exceptions for control flow, and should be avoided but it depends on your codebase if a query missing is never expected, then throwing might be the correct call but if you ever catch that error and handle it elsewhere, then I'd argue you should just have your GetCompany method return a Company? instead ie, make it clear that it can return nulls
Sonath
SonathOP13mo ago
basically this is the repo logic
public Company? GetCompany(Guid companyId, bool trackChanges) =>
// #TODO is new Company a good way to handle null return?
FindByCondition(company =>
company.Id.Equals(companyId), trackChanges)
.SingleOrDefault();
public Company? GetCompany(Guid companyId, bool trackChanges) =>
// #TODO is new Company a good way to handle null return?
FindByCondition(company =>
company.Id.Equals(companyId), trackChanges)
.SingleOrDefault();
idk if I should handle it differently using .SingleOrDefault() so if I make it clear that it can return nulls then I don't need conditional logic? but then how would I change the informational message that an entry was not found? Or is it not necessary? 👀
Pobiega
Pobiega13mo ago
you never mentioned what kind of app this is but again, if the query can return null, meaning no company with that id, then just check for null at the appropriate level if finding by ID shouldn't be able to fail (like the ID is not from the user), then thats a different story
Sonath
SonathOP13mo ago
ah sorry it's a Web API
Pobiega
Pobiega13mo ago
okay, but surely your controller/endpoint doesnt call the repository itself?
IsNotNull
IsNotNull13mo ago
In ASP.NET Core web controllers, you can return a not found response.
Pobiega
Pobiega13mo ago
and even if it does, I'd check for null and return a 404 or bad request or whatever there
IsNotNull
IsNotNull13mo ago
To let the client know that the thing it requested doesn't exist
Sonath
SonathOP13mo ago
yeah so, basically the custom exception does that, I just think that (after talking with others too) it's better NOT to throw an exception here, and reserve exceptions for really exceptional things.
Erroneous Fatality
Your approach is absolutely fine. You can do a short-hand version:
Company company = _repository.Company.GetCompany(companyId, trackChanges)
?? throw new ArgumentException("The company was not found.", nameof(companyId));
Company company = _repository.Company.GetCompany(companyId, trackChanges)
?? throw new ArgumentException("The company was not found.", nameof(companyId));
Be careful not to create too many specialized exception classes, if you're not actually catching them anywhere. For your usecase, I'd suggest just using an ArgumentException, and having a middleware set up in your API which transforms ArgumentExceptions to 400 HTTP status code responses. Also, you might want to use async communication in your repository.
Pobiega
Pobiega13mo ago
Using exceptions for control flow is not best practice.
Erroneous Fatality
Don't do .SingleOrDefault(), because that will make your queries more complicated. You should trust your Data set, your service code is the one maintaining it. It is absolutely fine.
Pobiega
Pobiega13mo ago
No, its not.
Erroneous Fatality
Do .FirstOrDefault() instead, no need to check on every query if your dataset is faulty.
Sonath
SonathOP13mo ago
the consumer may query for a company that doesn't exist
Pobiega
Pobiega13mo ago
handle the null appropriately and its not an issue.
Sonath
SonathOP13mo ago
yeah I think I agree with Pobiega, I'll remove the conditional checking and handle it differently
Erroneous Fatality
Using exceptions for exceptional cases is fine. I've made 10+ highly concurrent web apps in my career using this approach, haven't had a situation where I needed to optimize that. Alright, peace
Pobiega
Pobiega13mo ago
Its not about performance. its about intention and clarity of code. its not exceptinal that a query returned no results.. jesus christ.
Accord
Accord13mo ago
Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.
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