A project can become un-openable if you create the same example twice

[hahn-kev]

Describe the bug
Working on tasks in the frontend I ran into this issue, it should be prevented in the backend.

var entryId = ...;
var senseId = ...;
var example = new ExampleSentence {Id = Guid.NewGuid()};
api.CreateExampleSentence(entryId, senseId, example);
api.CreateExampleSentence(entryId, senseId, example);

Expected behavior
The second call should fail with an error.

Note

This issue was seen specifically on a FWData project

[rmunn]

Isn't there already code to prevent duplicates being created for some other types? Semantic domains or complex form types or the like? I remember seeing it but I couldn't find it just now.

[rmunn]

Found the code I was thinking of:

languageforge-lexbox/backend/FwLite/LcmCrdt/Changes/AddSemanticDomainChange.cs

Lines 12 to 17 in 2a4ea85

	public override async ValueTask ApplyChange(Sense entity, IChangeContext context)
	{
	if (entity.SemanticDomains.Any(s => s.Id == SemanticDomain.Id)) return;
	if (await context.IsObjectDeleted(SemanticDomain.Id)) return;
	entity.SemanticDomains.Add(SemanticDomain);
	}

[hahn-kev]

That's for harmony, this is a FWData issue

[myieye]

It's also possible to create duplicate parts of speech in FwData.
For some reason that only became noticeable in #2084.

The issue description suggests we should throw an error, but the CRDT API currently handles these cases by doing nothing and returning the current instance. It seems favorable to make both APIs work the same. I'm not quite sure what's best.