[BEAM-5306] Joins should support more than one output element from user joining UDF

• Type: Sub-task
• Status: Resolved
• Priority: P2
• Resolution: Fixed
• Fix Version/s: Not applicable
• Component/s: dsl-euphoria
• Assignee: Vaclav Plajt
• Reporter: Vaclav Plajt
• Created: 05/Sep/18 08:30
• Updated: 24/Jul/20 19:58
• Resolved: 07/Sep/18 11:43

Description

Output elements from joining user-defined functions are collected using `SingleValueCollector`, so only one output value is supported. That is wrong limitation. Refactor 'DoFnCollector' to be universally usable to collect many elements with custom adaptation.