Filter Choices for Combo Box

[Anonymous]

Most of what I've already found online is related to the old LookUp, so I figured I'd start a new question.

I'm trying to filter a Combo Box in a form so that it only contains valid/relevant options.

As an example, let's say I have a DataSource that's a table filled with various Olympians and I want a drop down where you select someone by name.

By default, the options for this field are set as:

Choices('Olympians'.Name)

which would display as options for the drop down every name found in the Name column in the table.

But, I want to limit their options to only, say, entries in the table that have their country set as Canada in another column.

The user can only access this form after selecting their country, so I don't want them editing forms and making Team Canada contain Team USA members, you know?

I've tried filtering it like this, but it didn't seem to work. Is there an error here, or is my understanding of how filtering works wrong?

Choices(Filter('Olympians', country_column = wantedCountryVariable).Name)

(The form used to use LookUps and after updating, it used this Choices() function I've not seen before, so pardon the possibly dumb usage of it)

UPDATE WITH MORE DETAILS

Here's more detailed information about my problem, which I'll edit the original post with for anyone else who happens to pop up in here:

In the actual data source I'm working with, it's a bunch of products where each row represents a product from a client. Not all products are associated with a support contract, but the user should be able to look through a list of the support contracts they have for other products and possibly apply it to another product (the combo box in question is this list). 

Using Choices(), this is why it's getting 1. All support contracts listed in the table, and 2. Blank ones, for the products that don't have contracts listed in the table/applied to the product. I want to filter the support contracts shown in the drop down by not displaying the blank ones and also only displaying the ones that are associated with the right client. There's a column in the table for contracts, and there's a column for client, so theoretically I thought something like this

Filter('Products', !IsBlank(Contract), ClientName = CurrentCustomer)

Would work, but so far no luck. This doesn't filter it at all and it also says it doesn't support the not operator. 

I'm pretty stuck at the moment!

[Sienna]

I have never use and never seen choices before. And it is also not listed in function reference page. Try to get rid of it

[Anonymous]

So how do I go about populating the Combo Box?

I'm assuming Choices is a newer function and has no reference on the reference page yet, because it's used in every combo box I've got so far.

The tool tip says it takes the values found in a given column and uses them to populate the Combo Box. It seems like exactly what I'm looking for, but lacking in an ability to filter the results.

[Sienna]

Ok Like I said I never heard of it so far and there is no reason to use it. Or at least I don’t see a reason here. Just put in your Items property

Filter('Olympians', country_column = wantedCountryVariable)

And set DisplayFields property of the combobox to whatever you want to display in your combobox

[Anonymous]

For some reason, I'm having a lot of difficulty getting this to work for the actual data source I'm using. I'll keep messing with it until I get somewhere though, because that looks like it should be right. The drop down appears exactly as it was before with Choices(), so it's as if it's not filtering anything at all. Another attempt I made by filtering by some other value left me with the right number of options, but all of them were blank. My theory is that it's displaying the wrong field of options, but it's limiting me to pick from a very specific list of fields which doesn't include the one I need.

Here's more detailed information about my problem, which I'll edit the original post with for anyone else who happens to pop up in here:

In the actual data source I'm working with, it's a bunch of products where each row represents a product from a client. Not all products are associated with a support contract, but the user should be able to look through a list of the support contracts they have for other products and possibly apply it to another product (the combo box in question is this list). 

Using Choices(), this is why it's getting 1. All support contracts listed in the table, and 2. Blank ones, for the products that don't have contracts listed in the table/applied to the product. I want to filter the support contracts shown in the drop down by not displaying the blank ones and also only displaying the ones that are associated with the right client. There's a column in the table for contracts, and there's a column for client, so theoretically I thought something like this

Filter('Products', !IsBlank(Contract), ClientName = CurrentCustomer)

Would work, but so far no luck. This doesn't filter it at all and it also says it doesn't support the not operator. 

I'm pretty stuck at the moment!

[Sienna]

To filter product from blanc and client name use

Filter('Products', !IsBlanc(Contract) && ClientName=CurrentCustomer) 

[Anonymous]

No difference again, nothing is being filtered out. I just get more Suggestions saying ! and && can't be evaluated remotely.

Thanks for sticking with me, lol.

[Sienna]

I think there is some limitation to isblank function. Im not at my computer so can’t test it but you can try to replace the isblank to !Contract=“”
Try it and see what you get

[Anonymous]

Same issue, not filtering anything at all.

[Sienna]

Ok so try to display CurrentCustomer variable in one label and see what value you get. If the label will be empty then you know the problem is in variable