Skip to main content

πŸ‘ Simple arrays

πŸ‘ Get all the Science Fiction Books​

Can I get all books for the genre Science Fiction?. Turns out it's quite simple:

[
  { 
    $match: { 
      genres: 'Science Fiction' 
    } 
  }
]

Remember that will include any book that has any other genre as long as it has Science Fiction in genres.

πŸ‘ Find all the books that belong at least to both genres "Fiction" and "Science Fiction"​

If you want to search for all books that have "Fiction" and "Science Fiction", in any order (and possibly other genres) use:

[
  {$match: { 
      genres: {$all: ['Science Fiction', 'Fiction'] } 
      } 
  },
  {$project: {
      title: 1,
      genres: 1
  }}
]

πŸ‘ Find books with either genre​

[{ 
    $match: {
      genres: { $in: ['Science Fiction', 'Fiction'] }
    }
  }
]

πŸ‘ Find all the books that belong only to the genres "Fiction" and "Science Fiction"​

In this case, we want books that have both "Fiction" and "Science Fiction" in the genres array and nothing else. So we're looking for documents that contain a genres array exactly as ['Fiction', 'Science Fiction']. We're not looking for the individual genres that could be inside the array, instead we are comparing the whole array on each document.

[
  {$match: { 
      genres: ['Fiction', 'Science Fiction'] 
    } 
  },
  {$project: {
    title: 1,
    genres: 1
  }}
]

Here we're comparing the whole array. Element order is important. With this comparison you'll get nothing in return:

[
  {$match: { 
      genres: ['Science Fiction', 'Fiction'] 
    } 
  },
  {$project: {
    title: 1,
    genres: 1
  }}
]