How can I access the value of an apex:repeat element?

Question

I have a Visualforce page that generates a comma-separated list of organization (account) IDs. I'd like to pass that list on to a report as a parameter.

In the example below, Organization Member is a junction object that connects Campaign and Account.

I'd like to have a link in the page, something like the following:

 <apex:outputLink value="/lightning/r/Report/00O1H000007mNBaUAM/view?fv0={!<???What goes
 here???>}">Important Report on Accounts in this campaign</apex:outputLink>

Note that this VF page is using the standard controller. I'd prefer a solution that didn't require a controller, but if a controller is necessary, I'll use it.

<apex:page standardController="Campaign" showHeader="false" sidebar="false" lightningStylesheets="true">

<apex:repeat value="{!Campaign.Organizational_Members__r}" var="account">
<apex:outputtext >{!account.Organization__r.id},</apex:outputText>
</apex:repeat>
<p>

</apex:page>

Can I get the full comma-separated value out of $Component in one piece or am I going to need to iterate through the individual values of the outputtext elements and gather them up somehow?

Answer 1

Doing this in pure Visualforce is ill-advised, mostly because it would need to use an unsupported (not undocumented, but rather, specifically called out in the documentation as unsupported) apex:variable within an apex:repeat.

However, you can easily do this with JavaScript:

<apex:page standardController="Campaign" showHeader="false" sidebar="false" lightningStylesheets="true">
    <script>
        let organizationIds = [];
        <apex:repeat value="{!Campaign.Organizational_Members__r}" var="account">
        organizationIds.push('{!account.Organization__c}');
        </apex:repeat>
        document.write(`<a href="/lightning/r/Report/00O1H000007mNBaUAM/view?fv0=${organizationIds.join(',')}">Important Report on Accounts in this campaign</a>`);
    <script>
</apex:page>

Other constructs are also possible, but this is one of the easiest ways to do this.