get length of array via variable just created mongodb - mongodb

Question

I am new to mongodb, I have a dataset that looks like the following, and I'm trying to Write an aggregation query that will determine the number of unique companies with which an individual has been associated.
Schema:
{
"_id" : ObjectId("52cdef7c4bab8bd675297d8b"),
"name" : "AdventNet",
"permalink" : "abc3",
"crunchbase_url" : "http://www.crunchbase.com/company/adventnet",
"homepage_url" : "http://adventnet.com",
"blog_url" : "",
"blog_feed_url" : "",
"twitter_username" : "manageengine",
"category_code" : "enterprise",
"number_of_employees" : 600,
"founded_year" : 1996,
"deadpooled_year" : 2,
"tag_list" : "",
"alias_list" : "Zoho ManageEngine ",
"email_address" : "pr#adventnet.com",
"phone_number" : "925-924-9500",
"description" : "Server Management Software",
"created_at" : ISODate("2007-05-25T19:24:22Z"),
"updated_at" : "Wed Oct 31 18:26:09 UTC 2012",
"overview" : "<p>AdventNet is now Zoho ManageEngine.</p>\n\n<p>Founded in 1996, AdventNet has served a diverse range of enterprise IT, networking and telecom customers.</p>\n\n<p>AdventNet supplies server and network management software.</p>",
"image" : {
"available_sizes" : [
[
[
150,
55
],
"assets/images/resized/0001/9732/19732v1-max-150x150.png"
],
[
[
150,
55
],
"assets/images/resized/0001/9732/19732v1-max-250x250.png"
],
[
[
150,
55
],
"assets/images/resized/0001/9732/19732v1-max-450x450.png"
]
]
},
"products" : [ ],
"relationships" : [
{
"is_past" : true,
"title" : "CEO and Co-Founder",
"person" : {
"first_name" : "Sridhar",
"last_name" : "Vembu",
"permalink" : "sridhar-vembu"
}
},
{
"is_past" : true,
"title" : "VP of Business Dev",
"person" : {
"first_name" : "Neil",
"last_name" : "Butani",
"permalink" : "neil-butani"
}
},
{
"is_past" : true,
"title" : "Usabiliy Engineer",
"person" : {
"first_name" : "Bharath",
"last_name" : "Balasubramanian",
"permalink" : "bharath-balasibramanian"
}
},
{
"is_past" : true,
"title" : "Director of Engineering",
"person" : {
"first_name" : "Rajendran",
"last_name" : "Dandapani",
"permalink" : "rajendran-dandapani"
}
},
{
"is_past" : true,
"title" : "Market Analyst",
"person" : {
"first_name" : "Aravind",
"last_name" : "Natarajan",
"permalink" : "aravind-natarajan"
}
},
{
"is_past" : true,
"title" : "Director of Product Management",
"person" : {
"first_name" : "Hyther",
"last_name" : "Nizam",
"permalink" : "hyther-nizam"
}
},
{
"is_past" : true,
"title" : "Western Regional OEM Sales Manager",
"person" : {
"first_name" : "Ian",
"last_name" : "Wenig",
"permalink" : "ian-wenig"
}
}
],
"competitions" : [ ],
"providerships" : [
{
"title" : "DHFH",
"is_past" : true,
"provider" : {
"name" : "A Small Orange",
"permalink" : "a-small-orange"
}
}
],
"total_money_raised" : "$0",
"funding_rounds" : [ ],
"investments" : [ ],
"acquisition" : null,
"acquisitions" : [ ],
"offices" : [
{
"description" : "Headquarters",
"address1" : "4900 Hopyard Rd.",
"address2" : "Suite 310",
"zip_code" : "94588",
"city" : "Pleasanton",
"state_code" : "CA",
"country_code" : "USA",
"latitude" : 37.692934,
"longitude" : -121.904945
}
],
"milestones" : [ ],
"video_embeds" : [ ],
"screenshots" : [
{
"available_sizes" : [
[
[
150,
94
],
"assets/images/resized/0004/3400/43400v1-max-150x150.png"
],
[
[
250,
156
],
"assets/images/resized/0004/3400/43400v1-max-250x250.png"
],
[
[
450,
282
],
"assets/images/resized/0004/3400/43400v1-max-450x450.png"
]
],
"attribution" : null
}
],
"external_links" : [ ],
"partners" : [ ]
}
Here is the query I tried:
db.companies.aggregate([{
$match: {
"relationships.person": {
$ne: null
}
}
}, {
$project: {
relationships: 1,
_id: 0
}
}, {
$unwind: "$relationships"
}, {
$group: {
_id: "$relationships.person",
count: {
$addToSet: "$relationships"
}
}
}])
I think I now need to get the length of the $relationships array? How would I do that?

Answer 1

When you only want the size of the array you really don't need to unwind...
Just use $size.
Alter your aggregation to:
db.companies.aggregate([{
$match: {
"relationships.person": {
$ne: null
}
}
}, {
$project: {
relationships: 1,
_id: 0,
relationship_size : { $size : "$relationships"}
}
}
}])
This should give you the result you want
From the comment i understand you want some more logic in the aggregation, from outta my head i would alter your aggregation to:
db.companies.aggregate([{
$match: {
"relationships.person": {
$ne: null
}
}
}, {
$project: {
relationships: 1,
_id: 0
}
}, {
$unwind: "$relationships"
}, {
$group: {
_id: "$relationships.person.permalink",
count : {$sum : 1}
}
}])
I can't find a "company name" in your relationships array so i use the permalink property