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!

[Anonymous]

Already done on the screen and it displays the proper value.

Having this:

Filter('Products', ClientName = CurrentCustomer)

Technically works for filtering (the number of options is cut down to whatever it is for that client), but every option is blank. DisplayFields always defaults to just "Value". This is the closest I've gotten to what I'm looking for.

I tried changing DisplayFields Value to some of the options listed when you go to the Properties tab of the Combo Box in question and click its Data, but none of those options are what I'm looking for.

[Sienna]

And your datasource is sharepoint? If so then i guess you will have to change something in the sharepoitnt but I have never worked with sharepoint so someone elese might probably help you more with this

[Anonymous]

Yup, Sharepoint.

I'll keep fiddling with it and see where it goes. Thank you for your help, though!

[Anonymous]

A bump just to ask anyone if I can at least filter out the blank values in a column when using Choices(), since that's the function that's working most consistently for me right now

[Jeff_Thorpe]

@Anonymous,

Here is a creative way to try and filter out the blank values. In my example Status is a single Choice column in a SharePoint list.

Filter(
  AddColumns(
    MySharePointList, "tmpStatus", Status.Value 
  ), 
  tmpStatus = Blank()
)

[Anonymous]

I'm not sure if I'm fully understanding the logic/what's going on with this, would you be able to elaporate a little more for me if you have the chance please?

[Jeff_Thorpe]

@Anonymous, does it work?

[Anonymous]

When I tried to use it, no, but I'm not entirely sure what it's doing so I could be using it wrong. Does this go in the Items property of it?

[Anonymous]

I think I got it filtering, but all values are appearing blank in the drop down. I think the issue is with DisplayFields and SearchFields, because they refuse to use the data I want because it's technically not a text field (or something along those lines)

[Jeff_Thorpe]

In my app it is working. The Status column in my example is a single select choice column in SharePoint. I have items in the list that never had a status selected, some with a status selected and then a few that had a status selected but then unselected. The normal Status.Value = Blank() was only returning the items that had previously had a value but is now blank.

By creating a tmp column I was able to store a blank value for both situations which are when the field doesn't have a value because it has never been selected or because the value was unselected. With the tmp field having a consistant blank value I was able to filter using TmpStatus = Blank().