How to remove field that has an empty string value using mongodb aggregation?-CodePudding

So far, after i tried, i came up with solution where i am able to remove the whole object inside of the array if that object has field with empty value. That does not work in my case. I only need to remove the field and keep rest of the object. In this case, "Comment" field is the one having empty values occasionally. Thanks in advance!

Structure:

someArray [
{
  field1:"value",
  field2:"value",
  Comment:""},
{
  field1:"value",
  field2:"value",
  Comment:""}]

Code:

    $project: {
      someArray: {
        $filter: {
          input: "$someArray", as: "array",
          cond: { $ne: [ "$$array.Comment", ""]}}}}

CodePudding user response：

Use $map to loop over the array elements.For each array element where comment is not an empty string, return whole element, otherwise return the document excluding comment field. Like this:

db.collection.aggregate([
  {
    "$project": {
      someArray: {
        $map: {
          input: "$someArray",
          as: "element",
          in: {
            $cond: {
              if: {
                $eq: [
                  "",
                  "$$element.Comment"
                ]
              },
              then: {
                field1: "$$element.field1",
                field2: "$$element.field2"
              },
              else: "$$element"
            }
          }
        }
      }
    }
  },
  
])

Here, is the working link.

CodePudding user response：

Solution from Charchit Kapoor works only if your array has exactly

{
  field1: ...
  field2: ...
  Comment:""
}

But it does not work for arbitrary fields. I was looking for more generic solution, my first idea was this:

db.collection.aggregate([
   {
      "$project": {
         someArray: {
            $map: {
               input: "$someArray",
               in: {
                  $cond: {
                     if: { $eq: ["$$this.Comment", ""] },
                     then: { $mergeObjects: ["$$this", { Comment: "$$REMOVE" }] },
                     else: "$$this"
                  }
               }
            }
         }
      }
   }
])

but it does not work.

I ended on this one:

db.collection.aggregate([
   {
      "$project": {
         someArray: {
            $map: {
               input: "$someArray",
               in: {
                  $cond: {
                     if: { $eq: ["", "$$this.Comment"] },
                     then: {
                        $arrayToObject: {
                           $filter: {
                              input: {
                                 $map: {
                                    input: { $objectToArray: "$$this" },
                                    as: "element",
                                    in: { $cond: [{ $eq: ["$$element.k", "Comment"] }, null, "$$element"] }
                                 }
                              },
                              as: "filter",
                              cond: "$$filter" // removes null's from array 
                           }
                        }
                     },
                     else: "$$this"
                  }
               }
            }
         }
      }
   }
])

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