Update all elements of an array, reading data from existing elements

[Raman_Gupta]

This seems like it should be easy but it seems to be annoyingly hard.

Input collection contains documents like this:

{
  "foo": [
    {
      "userId": "e736f24f-164e-46d1-8a8b-6ac2f69237a8",
      "params": {
        "location": {
          "coordinates": {
            "first": -80.514124,
            "second": 45.509854
          }
        },
        "withinDistance": 30,
        ... many other fields ...
      },
    },
    {
      "userId": "b71d2067-9dee-45cc-9903-7dea371ea685",
      "params": {
        "location": {
          "coordinates": {
            "first": -82.923723,
            "second": 47.210577
          }
        },
        "withinDistance": 30,
        ... many other fields ...
      },
    },
  ]
}

And I want to transform the non-standard foo.params.location.coordinates object into the standard GeoJSON format, so the output should look like this:

{
  "foo": [
    {
      "userId": "e736f24f-164e-46d1-8a8b-6ac2f69237a8",
      "params": {
        "location": {
          "type": "Point",
          "coordinates": [
            -80.514124,
            45.509854
          ]
        },
        "withinDistance": 30,
        ... many other fields ...
      },
    },
    {
      "userId": "b71d2067-9dee-45cc-9903-7dea371ea685",
      "params": {
        "location": {
          "type": "Point",
          "coordinates": [
            -82.923723,
            47.210577
          ]
        },
        "withinDistance": 30,
        ... many other fields ...
      },
    },
  ]
}

The closest I’ve come is this but I lose the withinDistance and other fields in the params structure:

db.collection.updateMany({}, [
  {
    "$set": {
      "foo": {
        "$map": {
          "input": "$foo",
          "as": "f",
          "in": {
            $mergeObjects: [
              "$$f",
              { 
                "params": {
                  "location" : {
                    "type": "Point",
                    "coordinates": [
                      "$$f.params.location.coordinates.first",
                      "$$f.params.location.coordinates.second"
                    ]
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
])

[steevej (Steeve Juneau)]

I think you are simply missing a extra $mergeObjects from the old params with the modified params.

[Raman_Gupta]

Thank you, that worked. I had actually tried that before, but now I realize I had missed the braces around the location object in the $mergeParams array, and MongoDB gave me a very strange error, which didn’t lead me to my error:

clone(t={}){const r=t.loc||{};return e({loc:new Position("line"in r?r.line:this.loc.line,"column"in r?r.column:...<omitted>...)} could not be cloned.

After your post I reviewed what I had done and found the missing braces.

For posterity, the solution looks like this:

db.collection.updateMany({}, [
  {
    "$set": {
      "foo": {
        "$map": {
          "input": "$foo",
          "as": "f",
          "in": {
            $mergeObjects: [
              "$$f",
              { 
                "params": {
                  $mergeObjects: [
                    "$$f.params",
                    {
                      "location" : {
                        "type": "Point",
                        "coordinates": [
                          "$$f.params.location.coordinates.first",
                          "$$f.params.location.coordinates.second"
                        ]
                      }
                    }
                  ]
                }
              }
            ]
          }
        }
      }
    }
  }
])

Thanks!