Count the Items in a Collection By Reusing a Data Loader
The simplest way to count the comments on a post is to use a Data Loader that returns all of the comments and return the length.
As long as the primary access pattern is to always fetch the number of comments along with the comments themselves, the Data Loader will batch them together and you'll get the count for free with no extra database requests.
Instructor: [0:02] If we want to count the comments for each post, the simplest way is to reuse our existing commentLoader and simply grab the length of the array that it returns. Let's add that to the schema, returning Int, and then test the query out. Getting a few zeros and a five, so the count is being returned correctly.
[0:26] If we are always going to query both commentCount and the list of comments at the same time, the DataLoader will batch them together, and we can essentially get the count for free with no extra database requests, which makes this the most efficient way to do it.