hj_zhang
(Hj Zhang)
December 31, 2020, 2:17am
1
Hi,everyone:
my code is here:
use('drug')
db.drug_insert.aggregate(
[ {
$unionWith: {
coll: { "$count": "total" }
}
} ]
)
but i get a error as below:
Error validating $unionWith value. err=Error getting coll field in $unionWith err=Expected ‘coll’ to be string, but got primitive.D instead
any help?my mongodb version is 4.4
Hi @hj_zhang ,
Welcome to MongoDB community!
Your syntax for the unionWith stage is not complete.
You need to specify a collection name to field coll
and your pipeline goes into field pipeline
.
For example to add the count of drug_insert
to the end of the query:
db.drug_insert.aggregate(
[ {
$unionWith: {
coll: "drug_insert", pipeline : [{ "$count": "total" }
}]
} ]
)
But to be honest you can just use the $count stage directly to just get the count.
Best
Pavel