If I have documents that look like this:
{
"items": [
{
"key": null
}
]
},
{
"items": [
{
"key": 2
}
]
}
]
... how can I find the document with 'key' set to null?
This is the query I've been trying, but I don't understand why it's returning both documents:
db.collection.find({
"items.0.key": {
$eq: null
}
})
nullnot only matches itself but also matches “does not exist.” Thus, querying for a key with the valuenullwill return all documents
https://www.oreilly.com/library/view/mongodb-the-definitive/9781449344795/ch04.html#sect2_d1e4021
Workaround: We need to perform a query with $type operator.
db.collection.find({
"items.0.key": {
$type: 10
}
})
$eq: null return the second document when items.0.key clearly exists and is not null ? And the rest of the quote is > Thus, querying for a key with the value null will return all documents lacking that key