Group By / Sum Aggregate Query with Parse Cloud Code

问题

I have Inventory table in my Parse database with two relevant fields: productId and quantity. When a shipment is received, a record is created containing the productId and quantity. Similarly, when a sale occurs, an inventory record is made with the productId and quantity (which will be negative, since the inventory will decrease after the sale).

I would like to run a group by/ sum aggregate query on the Inventory table with Parse Cloud Code that outputs a dictionary containing unique productIds as the keys and the sum of the quantity column for those Ids as the values.

I have seen a number of old posts saying that Parse does not do this, but then more recent posts refer to Cloud Code such as averageStart in the Cloud Code Guide: https://parse.com/docs/cloud_code_guide

However, it seems that Parse.Query used in averageStars has a maximum limit of 1000 records. Thus, when I sum the quantity column, I am only doing so on 1000 records rather than the whole table. Is there a way that I can compute the group by/ sum across all the records in the inventory table?

For example:

Inventory Table

productId quantity

Record 1: AAAAA 50

Record 2: BBBBB 40

Record 3: AAAAA -5

Record 4: BBBBB -2

Record 5: AAAAA 10

Record 6: AAAAA -7

Output dictionary: {AAAAA: 48, BBBBB: 38}

回答1:

You can use Parse.Query.each(). It has no limit. If your class has too many entries it will timeout though.

See docs

e.g.:

var totalQuantity = 0;
var inventoryQuery = new Parse.Query("Inventory");
inventoryQuery.each(
    function(result){
        totalQuantity += result.get("quantity");
    }, {
        success: function() {
            // looped through everything
        },
        error: function(error) {
            // error is an instance of Parse.Error.
        }
    });
});

If it times out, you have to build something like this.

回答2:

In case you want to see the code with the dictionary:

Parse.Cloud.define("retrieveInventory", function(request, response) {
  var productDictionary ={};
  var query = new Parse.Query("Inventory");
  query.equalTo("personId", request.params.personId);
  query.each(
     function(result){
        var num = result.get("quantity");
        if(result.get("productId") in productDictionary){
             productDictionary[result.get("productId")] += num;
        }
        else{
             productDictionary[result.get("productId")] = num;
        }
    }, {
        success: function() {
            response.success(productDictionary);
        },
        error: function(error) {
            response.error("Query failed. Error = " + error.message);
        }
    });
});

来源：https://stackoverflow.com/questions/26095204/group-by-sum-aggregate-query-with-parse-cloud-code

标签

group-by

parse-platform

sum

cloud

aggregate