Right now, it's not possible to use the $in operator in the $filter array aggregation operator.
Let's say this is the document schema:
{
_id: 1,
users: [
{
_id: 'a',
accounts: ['x', 'y', 'z']
},
{
_id: 'b',
accounts: ['j','k','l']
}
]
}
I want, using aggregate
, to get the documents with filtered array of users
based on the contents of the accounts
array.
IF the $in
would work with the $filter
operator, I would expect it to look like this:
db.test.aggregate([
{
$project: {
'filtered_users': {
$filter: {
input: '$users',
as: 'user',
cond: {
$in: ['$$user.accounts', ['x']]
}
}
}
}
}
])
and return in the filtered_users
only the first user since x is in his account.
But, as I said, this doesn't work and I get the error:
"invalid operator '$in'"
because it isn't supported in the $filter
operator.
Now I know I can do it with $unwind
and using regular $match
operators, but then it will be much longer (and uglier) aggregation with the need of using $group
to set the results back as an array - I don't want this
My question is, if there is some other way to manipulate the $filter
operator to get my desired results.
See Question&Answers more detail:
os 与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…