MongoDB query with conditional group by statement - mongodb

Question

I need to export customer records from database of mongoDB. Exported customer records should not have duplicated values. "firstName+lastName+code" is the key to DE-duped the record and If there are two records present in database with same key then I need to give preference to source field with value other than email.
customer (id,firstName,lastName,code,source) collection is this.
If there are record 3 records with same unique key and 3 different sources then i need to choose only one record between 2 sources(TV,internet){or if there are n number of sources i need the one record only}not with the 'email'(as email will be choosen when only one record is present with the unique key and source is email)
query using:
db.customer.aggregate([
{
"$match": {
"active": true,
"dealerCode": { "$in": ["111391"] },
"source": { "$in": ["email", "TV", "internet"] }
}
},
{
$group: {
"_id": {
"firstName": "$personalInfo.firstName",
"lastName": "$personalInfo.lastName",
"code": "$vehicle.code"
},
"source": {
$addToSet: { "source": "$source" }
}
}
},
{
$redact:
{
$cond: [
{ $eq: [{ $ifNull: ["$source", "other"] }, "email"] },
"$$PRUNE",
"$$DESCEND"
]
}
},
{
$project:
{
"source":
{
$map:
{
"input": {
$cond: [
{ $eq: [{ $size: "$source" }, 0] },
[{ "source": "email" }],
"$source"
]
},
"as": "inp",
"in": "$$inp.source"
}
},
"record": { "_id": 1 }
}
}
])
sample output:
{ "_id" : { "firstName" : "sGI6YaJ36WRfI4xuJQzI7A==", "lastName" : "99eQ7i+uTOqO8X+IPW+NOA==", "code" : "1GTHK23688F113955" }, "source" : ["internet"] }
{ "_id" : { "firstName" : "WYDROTF/9vs9O7XhdIKd5Q==", "lastName" : "BM18Uq/ltcbdx0UJOXh7Sw==", "code" : "1G4GE5GV5AF180133" }, "source" : ["internet"] }
{ "_id" : { "firstName" : "id+U2gYNHQaNQRWXpe34MA==", "lastName" : "AIs1G33QnH9RB0nupJEvjw==", "code" : "1G4GE5EV0AF177966" }, "source" : ["internet"] }
{ "_id" : { "firstName" : "qhreJVuUA5l8lnBPVhMAdw==", "lastName" : "petb0Qx3YPfebSioY0wL9w==", "code" : "1G1AL55F277253143" }, "source" : ["TV"] }
{ "_id" : { "firstName" : "qhreJVuUA5l8lnBPVhMAdw==", "lastName" : "6LB/NmhbfqTagbOnHFGoog==", "code" : "1GCVKREC0EZ168134" }, "source" : ["TV", "internet"] }
This is a problem with this query please suggest :(

Answer 1

Your code doesn't work, because $cond is not an accumulator operator. Only these accumulator operators, can be used in a $group stage.
Assuming your records contain not more than two possible values of source as you mention in your question, you could add a conditional $project stage and modify the $group stage as,
Code:
db.customer.aggregate([
{
$group: {
"_id": {
"id": "$id",
"firstName": "$firstName",
"lastName": "$lastName",
"code": "$code"
},
"sourceA": { $first: "$source" },
"sourceB": { $last: "$source" }
}
},
{
$project: {
"source": {
$cond: [
{ $eq: ["$sourceA", "email"] },
"$sourceB",
"$sourceA"
]
}
}
}
])
In case there can be more that two possible values for source, then you could do the following:
Group by the id, firstName, lastName and code. Accumulate
the unique values of source, using the $addToSet operator.
Use $redact to keep only the values other than email.
Project the required fields, if the source array is empty(all the elements have been removed), add a
value email to it.
Unwind the source field to list it as a field and not an array.
(optional)
Code:
db.customer.aggregate([
{
$group: {
"_id": {
"id": "$id",
"firstName": "$firstName",
"lastName": "$lastName",
"code": "$code"
},
"sourceArr": { $addToSet: { "source": "$source" } }
}
},
{
$redact: {
$cond: [
{ $eq: [{ $ifNull: ["$source", "other"] }, "email"] },
"$$PRUNE",
"$$DESCEND"
]
}
},
{
$project: {
"source": {
$map: {
"input":
{
$cond: [
{ $eq: [{ $size: "$sourceArr" }, 0] },
[{ "source": "item" }],
"$sourceArr"]
},
"as": "inp",
"in": "$$inp.source"
}
}
}
}
])