MongoDB using NOT and AND together

Question

I\'m trying to negate an $and clause with MongoDB and I\'m getting a MongoError: invalid operator: $and message back. Basically what I want to achieve

Answer 1

TLDR; You want a NAND Gate...

db.getCollection('test').find({ $or: [ {institution_type:{$ne:'A'}}, {type:{$ne:'C'}} ]})

... And then go thank (upvote) this answer (not me)

or a NOR Gate...

db.getCollection('test').find({ $nor: [{institution_type:'A', type:'C'}] })

---

Longer version...

I couldn't find a logical operator in MongoDB to handle $nand logic, so I "built" the logic (see below).

There is an open feature request for a $nand operator, but I wouldn't hold my breath (created 2014).

$nor can also do what you want, if you invert the $ne logic.

(But IMO - it feels like we're bastardising the behaviour - only using the inverse $not behaviour, and disregarding the $and behaviour of the array... but it works, so it's not wrong).

db.getCollection('test').insertMany([
    { "institution_type" : "A", "type" : "C" },
    { "institution_type" : "A", "type" : "D" },
    { "institution_type" : "B", "type" : "C" },
    { "institution_type" : "B", "type" : "D" }
])

// "NAND gate": (NOT A) OR (NOT B) -> correct 3x results
db.getCollection('test').find({ $or: [ {institution_type:{$not:{$eq:'A'}}}, {type:{$not:{$eq:'C'}}} ]})

// or simpler...
db.getCollection('test').find({ $or: [ {institution_type:{$ne:'A'}}, {type:{$ne:'C'}} ]})

// or simpler still...

// "NOR gate": (NOT A) AND (NOT B) -> correct 3x results
db.getCollection('test').find({ $nor: [{institution_type:'A', type:'C'}] })