how to find duplicate array value on document mongodb - arrays

Question

I got question might be many of you can help me.
so I have data on mongodb.
first data
{
"name" : 'david'
contacts : [
{
"name" : 'john',
"phone" : '123456'
},
{
"name" : 'george',
"phone" : '0987654'
}
]
}
second data
{
"name" : 'anita',
"contacts" : [
{
"name" : 'harry',
"phone" : '123456'
},
{
"name" : 'kurita',
"phone" : '323434'
}
]
}
the problem is,
can I query to find data that have duplicate contacts.phone.
so the result whill show like this.
{
"name" : 'david',
"contacts" : [
{
"name" : 'john',
"phone" : '123456'
}
]
}
{
"name" : 'anita',
"contacts" : [
{
"name" : 'harry',
"phone" : '123456'
}
]
}
data john and anita will show because they have similar data on contacts.phone
sorry for my english btw,
I hope you all understand what I mean.
thank you so much

Answer 1

There are a few steps involved to get the results you need.
We are going to write an aggregate pipeline to get the work done.
First you need to unwind your array values with the following:
{
$unwind: "$contacts"
}
Doc: https://docs.mongodb.com/manual/reference/operator/aggregation/unwind/
This would result into:
[
{
"_id": ObjectId("5a934e000102030405000000"),
"contacts": {
"name": "john",
"phone": "123456"
},
"name": "david"
},
{
"_id": ObjectId("5a934e000102030405000000"),
"contacts": {
"name": "george",
"phone": "0987654"
},
"name": "david"
},
{
"_id": ObjectId("5a934e000102030405000001"),
"contacts": {
"name": "harry",
"phone": "123456"
},
"name": "anita"
},
{
"_id": ObjectId("5a934e000102030405000001"),
"contacts": {
"name": "kurita",
"phone": "323434"
},
"name": "anita"
}
]
This would be much easier for us to group by field.
Doc: https://docs.mongodb.com/manual/reference/operator/aggregation/group/
{
$group: {
_id: {
phone: "$contacts.phone"
},
name: {
$addToSet: "$name"
},
contacts: {
$addToSet: "$contacts.name"
},
count: {
$sum: 1
}
}
}
That gives the following output:
[
{
"_id": {
"phone": "323434"
},
"contacts": [
"kurita"
],
"count": 1,
"name": [
"anita"
]
},
{
"_id": {
"phone": "123456"
},
"contacts": [
"john",
"harry"
],
"count": 2,
"name": [
"david",
"anita"
]
},
{
"_id": {
"phone": "0987654"
},
"contacts": [
"george"
],
"count": 1,
"name": [
"david"
]
}
]
Based on the output we need to match the count greater then 1 like:
Doc: https://docs.mongodb.com/manual/reference/operator/aggregation/match/
{
$match: {
count: {
"$gt": 1
}
}
}
Result is:
[
{
"_id": {
"phone": "123456"
},
"contacts": [
"john",
"harry"
],
"count": 2,
"name": [
"david",
"anita"
]
}
]
The query would look like:
Doc: https://docs.mongodb.com/manual/reference/operator/aggregation-pipeline/
db.collection.aggregate([
{
$unwind: "$contacts"
},
{
$group: {
_id: {
phone: "$contacts.phone"
},
name: {
$addToSet: "$name"
},
contacts: {
$addToSet: "$contacts.name"
},
count: {
$sum: 1
}
}
},
{
$match: {
count: {
"$gt": 1
}
}
}
])
MongoPlayground: https://mongoplayground.net/p/qSvhcYyAcQO
I hope this gives you a small idea what is possible with the aggregation pipeline.
Update / fix
According to your requirements you wish to have 2 objects foreach name that has duplicate contacts then you could use unwind again after the match.
[
{
"_id": {
"phone": "123456"
},
"contacts": [
"harry",
"john"
],
"count": 2,
"name": "david"
},
{
"_id": {
"phone": "123456"
},
"contacts": [
"harry",
"john"
],
"count": 2,
"name": "anita"
}
]
Cheers, Kevin