如何在 pymongo 中进行条件搜索？

Question

I am trying to make a conditional query. I want to search in the whole collection those documents that fit in range of prices of 25% and if the documents has a particular field(in this case 'audiPrice') I will use this field to do my search, and if this document hasn't the field, I will use a 'price' field

I have search in the mongodb documentation( https://docs.mongodb.com/manual/reference/operator/aggregation/cond/ ) and found the operator $cond and I have try to make a the query as you can see

pipeline = [
    {
        '$cond': {
            'if': {'audiPrice': {'$exists': True}}, 'then': {'$match':
                {'audiPrice': {
                    '$lte': price * 1.75, '$gte': price * 0.25
            }
                }
            },'else': {'$match': {
                'price': {
                    '$lte': price * 1.75, '$gte': price * 0.25
            }
            }


        }

    }
    }

]

and I got this error message

pymongo.errors.OperationFailure: Unrecognized pipeline stage name: '$cond'

Do you know how could I achieve my goal?

I am using python and pymongo.

thanks

Answer 1

You can use cond in $project or $expr in $match stage as:

collectionName.aggregate([
  {
    $match: {
      $expr: {
        $cond: {
          if: {
            $gt: [
              "$audiPrice",
              null
            ]
          },
          then: {
            $and: [
              {
                $gte: [
                  "$audiPrice",
                  price * 0.25
                ]
              },
              {
                $lte: [
                  "$audiPrice",
                  price * 1.75
                ]
              }
            ]
          },
          else: {
            $and: [
              {
                $gte: [
                  "$price",
                  price * 0.25
                ]
              },
              {
                $lte: [
                  "$price",
                  price * 1.75
                ]
              }
            ]
          }
        }
      }
    }
  }
])

Here you first check if field audiPrice is not null then perform the match on that key else on price key.