search on multiple collections with mongodb - mongodb

Question

I want to check if particular data is present on multiple documents or not.
eg I want to check if email exists in user collection and customer collection if it does then want to fetch the data.
I have tried below query but it fails as it checks only one collection.
db.t_usermasters.aggregate([
{
$match: {
"email" : "test#test.com"
}
},{
$lookup: {
from: "t_customermasters",
localField: "email",
foreignField: "email",
as: "UserDetails"
}
}
]).pretty();

Answer 1

if(db.t_usermasters.count({email: 'test#test.com'})
&& db.t_customermasters.count({email: 'test#test.com'})) {
/* fetch your data here
you can associate these two collections by using a customerId field in your
usermasters collection and then populate it ('customerId')
while fetching the data from usermasters collection */
}

Answer 2

Try this code:
db.t_usermasters.aggregate([
{
$match: {
"email" : "test#test.com"
}
},{
$lookup: {
from: "t_customermasters",
localField: "email",
foreignField: "email",
as: "UserDetails"
}
}, {
$match: {
UserDetails: { $exists: true, $not: {$size: 0} }
}
}
]).pretty();

Answer 3

You need to actually lookup in t_customermasters and project down by conditioning with empty array
db.t_usermasters.aggregate([
{
$match: {
"email" : "test#test.com"
}
},
{
$lookup: {
from: "t_customermasters",
localField:"email",
foreignField:"email",
as: "UserDetails"
}
},
{
$project:{
_id:true,
email:true,
emailExistInBoth:{
$cond:{
if:{
$eq:[{$size:"$UserDetails"},0]
},
then:false,
else:true
}
}
}
},
{
$match:{
"emailExistInBoth":true
}
}
]).pretty();