mongodb aggregate match not empty array code example

Example 1: mongodb check for array not empty query

collection.find({ arrayElementName: { $exists: true, $not: {$size: 0} } })

Example 2: mongodb filter empty array

db.collection.find({arrayElementName : {$exists:true, $size:0}})

Example 3: mongodb empty an array field

db.collection.update({}, { $set : {'myArray': [] }} , {multi:true} )