Trying to total columns for relation datasource

Question

I am putting together a PO Request manager.

I have created one model: PORequests

Then created a ONE to MANY relationship with another model: Items

Table on the left is the datasource: PORequests. The table on the right is PORequests:Items (relation)

So when you click on PORequest #1 on the left, you see only the items associated with that specific PO request.

Then when a user changes the quantity or cost of the item, the onValueEdit runs this code, creating an entry for the subtotal (a field in the Items model).

widget.datasource.item.Subtotal = widget.datasource.item.Quantity * widget.datasource.item.Cost;

All that works great, however now I want to add the subtoals for all the items and have it fill the Total field in the PORequest model.

How can I tell App Maker to add up all the subtotals for all items in PORequest #1?

Thank you for the help!

---

Update:

So I'm a little bit closer. I was able to get a label to display the total of subtotals. Stole the following Client Script from the Corporate Store template:

/**
 * Locale constant that is used for currency formatting.
 */
var CURRENT_LOCALE = 'en-US';


/**
 * Calculates and formats total cost of all POR items.
 * @param {Array<CartItem>} PORItems - list of user's POR items.
 * @return {string} formatted total cost of all POR items.
 */
function getSubtotalTotal(PORItems) {
  var cost = PORItems.reduce(function(result, item) {
    return result + item.Subtotal;
  }, 0);
  return '$' + cost.toLocaleString(CURRENT_LOCALE, {minimumFractionDigits: 2});
}

Then I put getSubtotalTotal(@datasource.items) as the text for the label.

So now I just need to figure out how to tell App Maker to take that result from the script and add it to the Total field in the PORequests datasource.

Answer 1

Okay, so here is what I did:

1. I created two Google Drive Table models: PORequests and Items.

PORequests has fields like: PORequest Number, Vendor and the Total*.

*Note: The Total field had to be a String and not a number.

Items has fields like: ItemName, Quantity, Cost and Subtotal.

2. I created a ONE to MANY relationship with the two datasources (PORequests as the owner).

3. I created a page with two Tables.

Table 1's datasource = PORequests Table 2's datasource = PORequests: Items (relation)*

This way if I click PORequest #1 in Table 1 I only see Items associated with that POR.

*Note: I set the Subtotal field to "non-editable/label", so no one accidentally changes it manually.

4. Then I created a Client Script:

/**
 * Locale constant that is used for currency formatting.
 */
var CURRENT_LOCALE = 'en-US';


/**
 * Calculates and formats total cost of all POR items.
 * @param {Array<CartItem>} PORItems - list of user's POR items.
 * @return {string} formatted total cost of all POR items.
 */
function getSubtotalTotal(PORItems) {
    var cost = PORItems.reduce(function(result, item) {
    return result + item.Subtotal;
  }, 0);
  var total = cost + app.datasources.PORequests_HideArchived.item.Tax + app.datasources.PORequests_HideArchived.item.Shipping;
  return '$' + total.toLocaleString(CURRENT_LOCALE, {minimumFractionDigits: 2});
}

5. Then I set the onValueEdit for the Quantity and Cost fields to:

widget.datasource.item.Subtotal = widget.datasource.item.Quantity * widget.datasource.item.Cost;

var subtotalTotal = getSubtotalTotal(app.datasources.PORequests.relations.Items.items);
app.datasources.PORequests.item.Total = subtotalTotal;

This tells App Maker to first: multiply the cost by the quantity and put that value in the Subtotal field.

Then it tells App Maker to: use the getSubtotalTotal script to add all the Subtotal values and put THAT value in the Total field of the PORequest datasource.

Hope all that helps someone in the future.