Question 236113 in Mongodb Question posted in
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How can I reference a field in MongoDB without knowing its name?

I’m trying to find all unique strings of some subdocument in MongoDB, as long as at least one of them contains a certain substring.
These strings are localized though.
I want to have the results for all possible languages.

So, my document would look something like this:

{
  ...
  "myLocalizedField": {
    "en": ...,
    "de": ...,
    "cz": ...
...
}

I do not know which languages are being used in the DB and not all documents use the same languages.

This is what my current pipeline looks like:

[
  {
    $match:
      {
        "I DON'T KNOW": {
          $regex: "my substring",
        },
      },
  },
  {
    $project:
      {
        myLocalizedField: 1,
      },
  },
  {
    $unwind:
      {
        path: "$myLocalizedField",
      },
  },
  {
    $group:
      {
        _id: {
          key: "I DON'T KNOW",
        },
      },
  },
]

I am unsure what to put in the $match and in the $group stages…

Tags:

2

Answers


  1. 0

    $objectToArray to rescue:

    [
  {
    $project: { localized: { $objectToArray: "$myLocalizedField" } }
  },
  {
    $unwind:
      {
        path: "$localized",
      },
  },
  {
    $match:
      {
        "localized.v": {
          $regex: "my substring",
        },
      },
  },
  {
    $group:
      {
        _id: {
          key: "$localized.k",
        },
      },
  },
]
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  2. 0

    You can use the $objectToArray operator:

    Pseudocode

    INPUT:
{"en":"foo", "de":"bar", "cz":"buz"} 
OUTPUT:
[{"k":"en", "v":"foo"}, {"k":"de", "v":"bar"}, {"k":"cz", "v":"buz"}]

    db.collection.aggregate([
  {
    "$addFields": {
      "tmp": {
        "$objectToArray": "$myLocalizedField"
      }
    }
  },
  {
    $match: {
      "tmp.v": {
        $regex: "llo"
      }
    }
  },
  {
    $unwind: {
      path: "$tmp"
    }
  },
  {
    $match: {
      "tmp.v": {
        $regex: "llo"
      }
    }
  }
])

    MongoPlayground

    Note: This solution doesn’t scale, since we reshape the document before searching.

    I recommend you to store your documents this way:

    {
  "myLocalizedField": [
    {"k": "en", "v": "Hello world"},
    {"k": "de", "v": "Hallo Welt"},
    {"k": "cz", "v": "Ahoj světe"},
    {"k": "es", "v": "Hola Mundo"},
  ]
}

    In this way the search is scalable and it is easier to apply filters.

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