Getting sum() of an attribute in loopback without looping through all instances of the object

Question

I have a model DummyModel that has the attributes attOne, attTwo and attThree.

To get all the instances of attOne, one can use-

DummyModel.find({where: {attTwo: 'someValue'}, fields: {attOne: true} });

The above query corresponds more or less to the MySQL query -

select attOne from DummyModel where attTwo = 'someValue'

However, I need to find the sum of all the attOne values returned from the above query. That is, the MySQL equivalent of -

select sum(attOne) from DummyModel where attTwo = 'someValue'

I read that loopback doesn't support aggregrate functions (i.e. groupby). But is there any way to getsum(attOne)?

I know one way is to get the object and then loop over all the instances and add it.

What I want to know is if there's any pre-existing loopback method to do the same.

Answer 1

Supposing that this code

f = DummyModel.find({where: {attTwo: 'someValue'}, fields: {attOne: true} });

returns an array like this

[
{attTwo: 'someValue' ,attOne: 1}
{attTwo: 'otherValue',attOne: 1}
]

you can use the reduce function to apply a function to all elements

var sum = f.reduce(function(last, d) {return d.attOne + last},0);

And here is the working code

DummyModel = {
  find: function(a) {
    return [{
      attTwo: 'someValue',
      attOne: 1
    }, {
      attTwo: 'otherValue',
      attOne: 2
    }];
  }
}

f = DummyModel.find({
  where: {
    attTwo: 'someValue'
  },
  fields: {
    attOne: true
  }
});

sum = f.reduce(function(last, d) {
  return d.attOne + last;
}, 0);

alert(sum);