Can you use $cond expression in $unwind stage?-CodePudding

I am trying to execute this unwind pipeline stage:

{
  path: {$cond: {
    if: {$size: {'$actionBy': {$gte: 2}}},
    then: '$actionBy',
    else: '$meta'
  }},
  preserveNullAndEmptyArrays: true
}

Error displayed is: 'expected a string as the path for $unwind stage, got object' which of course is self explanatory, but is there not a way to do this?!

CodePudding user response：

You can do it in two steps. Something like:

{$set: {data:
  {$cond: {
    if: {$size: {'$actionBy': {$gte: 2}}},
    then: '$actionBy',
    else: '$meta'
  }}
}},
{$unwind: {path: '$data', preserveNullAndEmptyArrays: true}}