findOne then findMany using value from document found in findOne, in a single query

const categorySlug = req.query.category;  const category = await Category.findOne({ slug: categorySlug });  const children = await Category.find({ parent: category._id });  

Is it possible to combine those two queries into one? I tried doing something like

const children = await Category.aggregate([        {          $match: {            slug: categorySlug,           },        },        {          // somehow use the _id field from document fetched in first stage         }      ]);  

But I have no idea if this is even possible.

EDIT:

const document = await Category.aggregate([        {          $match: {            slug: categorySlug,          },        },        {          $lookup: {            from: 'categories',            localField: '_id',            foreignField: 'parent',            as: 'children',          },        },      ]);        const desiredResult = document[0].children;  

This works but is there a way to do this fully in the aggregation pipeline? Basically I want to get ONLY the "children" array, nothing else.

https://stackoverflow.com/questions/66727802/findone-then-findmany-using-value-from-document-found-in-findone-in-a-single-qu March 21, 2021 at 08:34AM