Raymond,

Where are you going to show the total? If you have a table showing the child records, then you can set a column summary on the ‘Widgets’ field to Sum all of the records that show. Just be sure to add the condition of “LAST_MONTH” on the CreatedDate.

If you want to show the total on a detail page for the Parent, add an aggregate model for the Child and use a template field to show the total on the Parent detail page. Here is an example of the aggregate model for the number of Contacts for an Account.

Thanks for the suggestions, Bill. I want to display it on a table of the parent model where each row displays the total number of widgets that all children of that parent record made. I’m basically trying to recreate a roll up Salesforce field. Roll up fields don’t dynamically reset date ranges to reflect the current date( no “last month” option). I would like to recreate a rollup field that will determine if a group of child records occurred within a certain time frame and have that timeframe dynamically recalibrate based on today’s date. Thanks!

This is a great use case for the model lookup function in UI only formula fields.  Here is how: 

Create two models. 

Parent Model:   Includes record ID. 
Child Model: Aggregate model that aggregates the data in the children (sumValues), groups the children records by the ParentID, and filters with the “last Month” date literal. 

Then on the parent model add a UI only field of type “Formula” and give it syntax that looks somthing like this:

 MODEL_LOOKUP(“Parent”,“sumValues”,“ParentId”,{{Id}})   

Note.  The quotes on the first three properties are necessary, as is the merge syntax braces in the fourth. 

That should return the aggregation you are interested in. 

You may want to explore some model synching tools that have bee described elsewher ein the forum so that your Child model only includes the records from what is currently in memory for the parent model.  This will be important if you have lots of records…

Cheers. 

Sounds like a solution! I’ll give it a try and report back. Thanks!