How to find all in an array of array in MongoDB - arrays

Question

Below is the schema for an array contacts. The contacts array has a field hashtag which is another array. How do I find all the contacts which have a particular hashtag? For example all contacts with hashtag "zxc"?
"contacts" : [
{
"addedDate" : ISODate("2015-12-02T09:06:09.891Z"),
"personEmailId" : "tell.fadgfdg#gmail.com",
"_id" : ObjectId("565eb481bf35eeb83d7f9f13"),
"verified" : true,
"favorite" : true,
"linkedinUserName" : null,
"facebookUserName" : null,
"twitterUserName" : "IamlifePaul",
"count" : 2,
"relationshipStrength_updated" : 0,
"contactRelation" : {
"decisionmaker_influencer" : null,
"prospect_customer" : "prospect"
},
"source" : "abc",
"mobileNumber" : "3546789",
"skypeId" : "123",
"designation" : "test",
"companyName" : "Something",
"location" : "Hyderabad, Telangana, India",
"personName" : "Naveen Paul",
"personId" : "565022d7dbeaeb9e17fc7083",
"hashtag" : [
"latestTag",
"anotherTag",
"#hash",
"openLove",
"hellTwo",
"working?",
"hello",
"lol",
"zxc"
],
"lastInteracted" : ISODate("2015-12-08T05:07:53.746Z")
},
{
"addedDate" : ISODate("2015-12-02T09:06:09.891Z"),
"personEmailId" : "naveenpaul.fadgfdg#gmail.com",
"_id" : ObjectId("565eb481bf35eeb83d7f9f13"),
"verified" : true,
"favorite" : true,
"linkedinUserName" : null,
"facebookUserName" : null,
"twitterUserName" : "IamlifePaul",
"count" : 2,
"relationshipStrength_updated" : 0,
"contactRelation" : {
"decisionmaker_influencer" : null,
"prospect_customer" : "prospect"
},
"source" : "abc",
"mobileNumber" : "3546789",
"skypeId" : "123",
"designation" : "test",
"companyName" : "Something",
"location" : "Hyderabad, Telangana, India",
"personName" : "Naveen Paul",
"personId" : "565022d7dbeaeb9e17fc7083",
"hashtag" : [
"latestTag",
"anotherTag",
"#hash",
"openLove",
"hellTwo",
"working?",
"hello",
"lol",
"zxc"
],
"lastInteracted" : ISODate("2015-12-08T05:07:53.746Z")
},
{
"addedDate" : ISODate("2015-12-02T09:06:09.891Z"),
"personEmailId" : "naveenpaul.fadgfdg#gmail.com",
"_id" : ObjectId("565eb481bf35eeb83d7f9f13"),
"verified" : true,
"favorite" : true,
"linkedinUserName" : null,
"facebookUserName" : null,
"twitterUserName" : "IamlifePaul",
"count" : 2,
"relationshipStrength_updated" : 0,
"contactRelation" : {
"decisionmaker_influencer" : null,
"prospect_customer" : "prospect"
},
"source" : "abc",
"mobileNumber" : "3546789",
"skypeId" : "123",
"designation" : "test",
"companyName" : "Something",
"location" : "Hyderabad, Telangana, India",
"personName" : "Naveen Paul",
"personId" : "565022d7dbeaeb9e17fc7083",
"hashtag" : [
"polly",
"tagger",
"#hash",
"working?",
"hello",
"lol",
"zxc"
],
"lastInteracted" : ISODate("2015-12-08T05:07:53.746Z")
}
I did this query - db.myColl.find({"contacts.hashtag":"zxc"},{"contacts":{$elemMatch:{"hashtag":"zxc"}}}).pretty()
which returned only one contact. I need to get all contacts.

Answer 1

You can do it via aggregation framework:
1) Do an initial match to reduce the input set for aggregation
2) Unwind contacts field.
3) Filter out contacts with hashtag 'zxc'
4) Group by id and put contacts on "contacts" field.
db.getCollection('contacts').aggregate([
{$match: {"contacts.hashtag":"zxc"}},
{$unwind: "$contacts"},
{$match: {"contacts.hashtag":"zxc"}},
{$group: {_id:"$_id", "contacts": {$push:"$contacts"}}}
])

Answer 2

You can use
For multiple hashtag in single doc
db.myColl.find({"contacts.hashtag":{$in : ['zxc','anotherTag']}});
//will return all doc with any of the two hashtags.
For single hashtag
db.myColl.find({"contacts.hashtag":'zxc'});
//return all documents with hashtag 'zxc'
Please refer $in