CODEWITHSUNDEEP
mongodbstudio3t
Dylanz
Dylanz

Reputation: 15

How can I print one object from inside an array for a list of documents?

I've got about 50k documents that have many fields, but the important ones for this issue look like this:

"_id": ObjectId(""),
...
"item": "apple"
"properties" : [
 {
    "color": "red",
    "size" : "L",
    "status": "eatable"
 }
],
...

What I'm trying to print are lines that look like item+";"+properties.color, while retaining the integrity of the data I have, and printing these fields only for certain documents. For now the only thing I've had success with is printing either only the item or the whole array "properties", but I can't get neither the two of them at the same time nor just the color.

db.getCollection("foods").find({properties:{$elemMatch:{color: {$in:["red", "green", "orange", "blue"]}}}})
.aggregate([
   { $unwind: {path:"$properties", preserveNullAndEmptyArrays: true}},
   ]).forEach(function(row){
       if(row.properties !== undefined) print (row.item + ";" + row.properties.color) })

This gives an error, because of the find before the aggregate, but I don't really know how else to make it so that it only prints this for the rows that fit that condition (and I also don't really know if the $unwind would mess up the arrays in my data, or if it is just a temporary "separation" while the function is running).

What I've got running right now, getting just the items:

db.getCollection("foods").find({properties:{$elemMatch:{color: {$in:["red", "green", "orange", "blue"]}}}})
.forEach(
   function(row){
       print (row.item) 
   }
)

By changing row.item to row.properties I got the full arrays printed, but adding .color after that did nothing.

Upvotes: 1

Views: 104

Answers (1)

J.F.
J.F.

Reputation: 15235

Not sure if I'm understood but what about to prepare data into the query like this:

db.getCollection("foods").aggregate([
  {
    $match: {
      "properties.color": {
        $in: [
          "red",
          "green",
          "orange",
          "blue"
        ]
      }
    }
  },
  {
    $project: {
      _id: 0
      item: 1,
      color: {
        "$arrayElemAt": [
          "$properties.color",
          0
        ]
      }
    }
  }
])

Example here.

And getting something like this JSON below you can iterate easily and access to color and item property.:

[
  {
    "color": "red",
    "item": "apple"
  }
]

Upvotes: 1

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