.NET Core provider: Selecting only empty label key-values is unclear.

[jimmyca15]

Some of the key-values in my configuration store's have multiple labels. For example I have the key-value "abc" which exists with an empty label and also with a label named "someLabel".

I wanted to use the .NET Core config provider to query the key-values with an empty label. For some reason I was expecting key-values with a null label to always take priority. What I found was that when I accessed configuration["abc"] it returned the value of the abc key-value in the "someLabel" label.

Then I tried to figure out how to query only empty label key-values with the provider but it wasn't as easy as I would have liked. I need to call

            builder.AddAzconfig(o => {
                o.ConnectWithManagedIdentity("https://mystore.azconfig.io");
                o.Use("*", "\0"); // This selects key-values with the empty label.
            });

I believe we need to make the empty label filter a constant within the provider and perhaps add documentation to the method which describes that this constant should be used to select only key-values that have the empty label.

[zhenlan]

This is because we load everything by default and while we put them in a dictionary, the last one wins.

Don't o.Use("*", "") or o.Use("*", null) work for empty label?

Yes, we should have predefined KeyFilter.Any and LabelFilter.Empty.

Do we like to have a helper function below too?

public AzconfigOptions UseLabel(string labelFilter, DateTimeOffset? preferredDateTime = null)

[zhenlan]

@yijiamicrosoft probably can help on this.

[jimmyca15]

I think the helper function might just overpopulate the code. I would opt for the LabelFilter.Empty and a mention in the method's documentation of when to use that constant.

[zhenlan]

Sounds good. And KeyFilter.Any?

[jimmyca15]

@zhenlan I like that idea.

[zhenlan]

We have a weird behavior currently

• If a user does not call Use(...) at all, we default to load all labels.
• If a user simply calls Use("*"), we default to load empty label only.

I think this partially contributes to the unexpected results @jimmyca15 described at the beginning of this thread. From users' perspective, it's not very useful to let different labels just step on each other and have an underminstic result.

Therefore, I think we should change our default behavior to only load empty label when Use(...) is not called. Thoughts?

[Yiming-Jia]

@jimmyca15 @zhenlan I'll send out a PR to change default behavior (user doesn't call Use(...)) to load \0 labels.

[jimmyca15]

I'm not opposed to that. We can also describe that behavior in the method summary.

Another concern is that we currently don't allow "*" in label filters. We throw an ArgumentException if any character is a "*". This might be outdated, and we should probably support the ability to do .Use(KeyFilter.Any, LabelFilter.Any)

[Yiming-Jia]

Talked with @zhenlan, if we put LabelFilter.Any, the behavior becomes unpredictable right now. We might want to constrain user not using *.

[zhenlan]

This is fixed.