Recursive Nested Arrays - Applying query to multiple array

Question

{
  "array": [
    {
      "date1": "date1",
      "date2": "date2",
      "childArray": [
        {
          "date1": "date1",
          "date2": "date2",
          "childArray": [
            {
              "date1": "date1",
              "date2": "date2"
            }
          ]
        }
      ]
    }
  ]
}

I have document that is of the format above - I need to be able to query give a date and fetch all recursively here if the date falls between date1 and date2.

Could use a bit of help -- I've looked into aggregation and a way of potentially flattening this structure out via the aggregation and then applying the query but I haven't gotten anywhere with it.

This is a sample -- the childArray can be any number of layers deep, so need something recursive.

Joe · Accepted Answer · 2020-08-13 02:46:56Z

1

You can do this with a find and $or:

var date = ISODate("2020-08-12T23:45:00Z")
db.collection.find({
    $or: [
          {array: { $elemMatch:{
                date1: {$lte: date},
                date2: {$gte: date}
          }}},
          {"array.childArray": { $elemMatch:{
                date1: {$lte: date},
                date2: {$gte: date}
          }}},
          {"array.childArray.childArray": { $elemMatch:{
                date1: {$lte: date},
                date2: {$gte: date}
          }}}
    ]
})

answered Aug 13, 2020 at 2:46

Joe

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4 Comments

aspiringCoder Over a year ago

Thanks Joe - updating my question -- it should state that I don't actually know how deep this childArray nesting can go, so I need some sort of recursive query.

Joe Over a year ago

The mongo query language doesn't do looping, branching, or recursion. A BSON object is limited to 16MB, so there is an upper limit on the possible nesting in the document. You could programmatically create an $or array like this that is thousands deep and query with that.

aspiringCoder Over a year ago

Another option I was thinking was that --- could we somehow flatten that array by using map or something --- then query that flattened array.. so take the children and children of children and move them into a single flat array, again that could be done programatically

Joe Over a year ago

There would need to be a match in the fields of each array for graphLookup. Neither the mongo query language or aggregation have an operator to recursively flatten and array. You could use $unwind repeatedly, but your query would still only handle up to a specific depth.

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