Merge two array items into one based on common field in MongoDB - mongodb

Question

I have following following collection (in Json format) -
/* 1 */
{
"_id" : NumberLong(1111),
"valueArray" : [
{
"accountNumber" : NumberLong(12345),
"levels" : [
1,
13
]
},
{
"accountNumber" : NumberLong(67890),
"levels" : [
2
]
}
]
}
/* 2 */
{
"_id" : NumberLong(2222),
"valueArray" : [
{
"accountNumber" : NumberLong(33333),
"levels" : [
13,
1
]
},
{
"accountNumber" : NumberLong(33333),
"levels" : [
8
]
},
{
"accountNumber" : NumberLong(44444),
"levels" : [
5
]
}
]
}
Notice the 2nd document where accountNumber is same (33333). I want to merge these into single entry. The output should look like -
/* 1 */
{
"_id" : NumberLong(1111),
"valueArray" : [
{
"accountNumber" : NumberLong(12345),
"levels" : [
1,
13
]
},
{
"accountNumber" : NumberLong(67890),
"levels" : [
2
]
}
]
}
/* 2 */
{
"_id" : NumberLong(2222),
"valueArray" : [
{
"accountNumber" : NumberLong(33333),
"levels" : [
13,
1,
8
]
},
{
"accountNumber" : NumberLong(44444),
"levels" : [
5
]
}
]
}
I tried multiple approaches $concatArrays, $setUnion etc but I end getting some or other error. Even if I am able to get some output, it is not in required format.
Can someone please help here?

Answer 1

You can use double $unwind to get single document per valueArray.accountNumber and the double $group to aggregate those values, initialy by accountNumber and then by _id, try:
db.col.aggregate([
{
$unwind: "$valueArray"
},
{
$unwind: "$valueArray.levels"
},
{
$group: {
_id: {
_id: "$_id",
accountNumber: "$valueArray.accountNumber"
},
levels: { $push: "$valueArray.levels" }
}
},
{
$group: {
_id: "$_id._id",
valueArray: {
$push: { accountNumber: "$_id.accountNumber", levels: "$levels" }
}
}
}
])