处理MongoDB查询结果中不存在的子文档的最佳方法

Question

I know this question has been asked before in some shape or form but I am looking for the best way to handle query results without a lot of if statements.

Let's say I am looking for a product (sub-document) in a package (document)

Packages.find({_id : req.body.packId, "products._id" : req.body.prodId})
   .exec(function(err, result){
     if(err) throw err;

    // make sure the result array exists and is not empty

     if(result && result.length > 0) {

       // make sure product array exists and is not empty

        if(result.products && result.products.length > 0){
           res.json(result);
           }
          }
        });

I noticed I cannot do:

if(result.products.length > 0)

If there is no product, node will crash since it cannot determine 'length' of undefined.

My question is: Is there a better way to do this?

Answer 1

It looks like you are already checking the products_id, so it should never be null if it is returned.

Another way you could do it is by checking that the field is populated in the query.

db.Packages.find({ "products.": { $exists: true, $ne: null } })

You can make the check in the query itself so that you don't have to check in code.