C# LINQ3 array positional operator no longer works?

[Renn]

I have been using the new C# beta driver with LINQ3 support, which is fantastic because it supports much more complex queries than the previous one. But I also noticed that being able to use -1 as a positional operator no longer appears to work when calling UpdateOneAsync (and probably UpdateManyAsync and its synchronous cousins).

For example, the following code ran just fine in LINQ2:

await collection.UpdateOneAsync(l => l.Id == another.Id && l.AnArrayMember.Any(l => l.Id == anArrayId),
                    Builders<ModelClass>.Update.Set(l => l.AnArrayMember.ElementAt(-1).Deleted, true));

This now fails with the error Cannot create field '-1' in element [...], where before it successfully translated it into AnArrayMember.$.Deleted and the Set command completed fine.

Has the use of this changed? Is there another way to perform this operation with LINQ3?

Thanks in advance for your help!

[James_Kovacs]

Hi, Renn,

Thank you for reaching out to us. This appears to be an unintentional difference in behaviour between LINQ2 and LINQ3. In LINQ2, we used -1 as a magic number to indicate the use of the positional operator, but this was not carried over to LINQ3. I have created CSHARP-4079 to track this bug.

We appreciate you reporting this issue. Please follow CSHARP-4079 for updates.

Sincerely,
James

[Renn]

Hi James, greatly appreciated. I’ve found a work-around by not using LINQ expressions in the Set operation, but of course a strongly-typed LINQ-compatible way of doing this would be preferable.

Thanks again for looking into this and hopefully this will be resolved in future builds.