// used when the record you're looking for has the _id as a type of ObjectId.
db.pets.find({ _id: ObjectId('id_string here...') })

db.pets.findOne({ _id: ObjectId('id_string here...') })

// for our manually entered _ids where there is no "ObjectId" in the _id field.
db.pets.find({ _id: '1' });

db.pets.findOne({ _id: '1' });