如何汇总猫鼬集合？

Question

In my mongoose model I have an invoiceHeader and invoiceLine collection both relating to account object. In a view I want to display the total invoiceAmount for the account. In SQL something like select sum(amount) from invoiceHeader group by account. How can i achieve similar with nodeJS and mongoose?

Answer 1

Assuming amount is the property that you want to sum on, it would be like:

InvoiceHeaderModel.aggregate({
  $match: {
    account: '<Account_ID>'
  }
}, {
  $group: {
    _id: null,
    total: {
      $sum: "$amount"
    }
  }
}, {
  $project: {
    _id: 0,
    total: 1
  }
}, function(err, res) {
  // res contains the result
});

The $match operator is used to match certain documents. The $group operator is used to group the documents. The $project operator is used to select certain fields from the documents.