How to merge Array value with key name in mongo db

Question

{
    _id :{
        "foo" : "abc"
    },
    "time" :[],
    "bar": [
        [],
        []
    ]
}

Expected Output abc become the key bar

{
    "_id" :{
        "foo" : abc
    },
    "time" :[],
    "abc": [
        [],
        []
    ]
}

it's not working in my case, I have multiple documents, or can you describe me in detail or post some query, that would be helpful — bc110402922
– bc110402922, Commented Nov 5, 2020 at 15:00
Can you provide a better example and explanation?. With this data I'm assuming you only want to rename bar to abc. But, is abc given or is neccesary get from the _id.foo field? — J.F.
– J.F., Commented Nov 5, 2020 at 15:02
yes, it is compulsory to get from _id.foo. so, abc is dynamically changing, but bar is the key name, it contains the values of abc Expeceted result is abc as the name of array and get values. — bc110402922
– bc110402922, Commented Nov 5, 2020 at 15:05
do you want to update update() this documents? or just want to get and display aggregate() ? — turivishal
– turivishal, Commented Nov 5, 2020 at 15:12

turivishal · Accepted Answer · 2020-11-05 15:26:01Z

1

You can try,

$arrayToObjects to set foo as k(key) and bar as v(value) and convert to object format
$mergeObjects to merge $$ROOT and above operation result
$replaceRoot to replace above both merge object result in root
$project to remove bar field because we don't needed

db.collection.aggregate([
  {
    $replaceRoot: {
      newRoot: {
        $mergeObjects: [
          { $arrayToObject: [[{ k: "$_id.foo", v: "$bar" }]] },
          "$$ROOT"
        ]
      }
    }
  },
  { $project: { bar: 0 } }
])

Playground

answered Nov 5, 2020 at 15:26

turivishal

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11 Comments

bc110402922 Over a year ago

your sol is work if I have documents as an array but I don't have the document as array. I have structure like this { _id :{ "foo" : "abc" }, "time" :[], "bar": [ [], [] ] } your sol is work IF [ _id :{ "foo" : "abc" }, "time" :[], "bar": [ [], [] ] ]

turivishal Over a year ago

Yes its an array its just structure of playground website, you can run this query in your platform this will work.

bc110402922 Over a year ago

When I run it , I get error message : '$arrayToObject requires an object keys of 'k' and 'v'. Found incorrect number of keys:1' on server .

turivishal Over a year ago

have you executed same query?

bc110402922 Over a year ago

yes, I executed, the same query as you give. but as I said I have one document with { } your query is working with [ ].

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