Question on Quiz 4

MongoDB University M001: MongoDB Basics
#1

my thinking is mistaken & how I should frame the problem:

I am using Compass: the goal is to restrict data size and return content with an array matching some values.
as an example from Airbnb sample data: I get this from the query below: unknown operator $and

{amenities:{$and:[{$size:20},
{$all:["Pool","Microwave","WiFi"]}
]}}

Both parts individually are validstrong text :

{amenities:{$size:20}}

and

{amenities:
{$all:["Pool","Microwave"]}
}

If I pull $and to top-level as in :

{$and:[expression1, exprression2]}  it still is not valid
eg: {$and:[amenities:{{$size:20},
{$all:["Pool","Microwave"]}
]}

What have I got backward? Thanks!

#2

You are really close to the correct query.

You are correct with

but expression1 is

and expression2 is

The major issue is that you factored amenities. The correct query is

{ "$and" : [
  { "amenities" : {$size:20} } ,
  { "amenities" : {$all:["Pool","Microwave"]} }
] }

Note that inside an array you have simple values, like strings or numbers, objects (enclosed inside {}) or arrays (enclosed inside[]).

By factoring amenities you were on the right track to use implicit and rather than explicit $and. With implicit and, that is with amenities factored, the query would look like:

{ "amenities" : {
  "$size" : 20 ,
  "$all" : ["Pool","Microwave"]
} }

You could even add a $nin such as

{ amenities: {
  $size: 20 ,
  $all: [ 'Pool', 'Microwave'] ,
  $nin: [ 'Cable TV']
} }
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#3

thanks for both the examples and clarity !!! You help is wonderful !

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#4