Mongodb：如果在第一个集合中找不到数据，则在另一个集合中查找

Question

I want to find data from either of 2 collections. If the data is not found in first, it must look into the second collection.

I tried to use $lookup with aggregation pipeline, but somehow, it won't work in the present case.

I am using Mongoose here (version 4.10.8)

I have DestinationPage as one collection, where I find a document matching with destinationPage_name , if I don't get the data (will return null, if so) then I wish to find it in SpecialityPage collection matching with specialityPage_name .

 DestinationPage.aggregate([
        { "$match" : { "destinationPage_name": { $regex: SEARCH_REF_DESTINATION, $options: 'i' } }},
        { "$lookup" : {
            "from" : "SpecialityPage",
            "localField" : "specialityPage_name",
            "foreignField" : { $regex: SEARCH_REF_DESTINATION, $options: 'i' },
            "as" : "data2"
          }
        },

      ]).then(doc => {
        console.log('document', doc);
      })
      .catch(err => {
        console.error("got error : ", err);
      })

The above code gives error as,

"The 'cursor' option is required, except for aggregate with the explain argument"

If I add { cursor:{} } to it, I don't see even console printing.

OPTION: I can check data in one collection, then if I don't get any data, then in callback, I can check another collection. However I don't consider it as a efficient way of doing.

Thanks.

'#stayhomestaysafe'

Answer 1

Your mongoose version is not compatible with MongoDB v4.10.8 .

You need to upgrade to the recent version v5.9.9

MongoDB Server Version Compatibility