MongoDB aggregate chain from matches

Question

My targred is to exclude records which are already mateched from previous match aggregation in MongoDb.

In first match I need to fetch records from two countries: United States and Germany.

In second match I need to exclude records from given country, for example United States AND level of "Begginer", but keep other records from United States and Germany. How is that possible? Example Data:

[
  {
    country: 'United States',
    personName: 'John',
    level: 'Average',
  },
  {
    country: 'United States',
    personName: 'Rina',
    level: 'Begginer',
  },
  {
    country: 'Germany',
    personName: 'John',
    level: 'Average',
  }
]

First match (correct):

{
  country: {$in: ['United States', 'Germany']}
}

Second match (wrong):

{
  $and: [
    { level: { $ne: 'Begginer'} },
    { country: { $eq: 'United States' } },
  ]
}

I do not want to add countries array again in second match phase.

Answer 1

You'll need an $or so that you keep all records that are not 'United States':

db.stuff.aggregate([
  { $match: {
      country: {$in: ['United States', 'Germany'] }
    }
  },
  { $match: {
      $or: [
        { country: { $ne: 'United States' } },
        { country: { $eq: 'United States' }, level: { $ne: 'Begginer'} }
      ]
    }
  }
]);

You can then just combined the 2 matches in to one.

db.stuff.aggregate([
  { $match: {
      country: {$in: ['United States', 'Germany'] },
      $or: [
        { country: { $ne: 'United States' } },
        { country: { $eq: 'United States' }, level: { $ne: 'Begginer'} }
      ]
    }
  }
]);

Both these queries will output:

{
        "_id" : ObjectId("5e999bdee125b211df7f361a"),
        "country" : "United States",
        "personName" : "John",
        "level" : "Average"
}
{
        "_id" : ObjectId("5e999bdee125b211df7f361c"),
        "country" : "Germany",
        "personName" : "John",
        "level" : "Average"
}

https://mongoplayground.net/p/oXBqAzBHzUr