MongoDB find records with empty array or array match

Question

I have a set of records like the following:

[ 
  { title: 'foo', members: [ 'a', 'b' ] },
  { title: 'bar', members: [] },
  { title: 'fiz', members: [ 'b' ] }
]

The members prop is used for restricting certain records so what I'm hoping to do is check the property and if empty or doesn't exist OR it contains the member return the item.

For example:

User a would get back foo (is a member) and bar (no member restrictions)
User b would get all three because they are a member on 0 and 2 and no member restrictions are set on on 1

Try var user = 'a'; db.collection.distinct('title', { '$or': [ { 'members': user }, { 'members.0': { '$exists': false } } ] }); — chridam
– chridam, Commented Feb 12, 2020 at 16:45

Valijon · Accepted Answer · 2020-02-12 16:46:08Z

3

Something like this:

db.collection.find({
  $or: [
    {
      "members.0": {
        $exists: false
      }
    },
    {
      "members": "User"
    }
  ]
})

MongoPlayground

or

db.collection.find({
  $or: [
    {
      $expr: {
        $eq: [
          {
            $size: "$members"
          },
          0
        ]
      }
    },
    {
      "members": "User"
    }
  ]
})

answered Feb 12, 2020 at 16:46

Valijon

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