SharePoint Sandboxed Custom Workflow Activity to get value from another list based on multiple criteria

Question

I'm trying to write a sandboxed custom workflow activity that would go to another list and get a value of a field based on values of multiple other fields combined.

List A

• State - lookup to States list
• City - lookup to Cities list
• Population - Number
• ... other columns

(essentially the combination of State and City makes the row uniquely identifiable)

List B

• Company - lookup to Companies list
• State - lookup to States list
• City - lookup to Cities list
• Affecting % of population - number (percent)
• Population Affected - Number field (to be filled in by the custom activity workflow)
• ... other columns

Constrains:

• I can't add Company field to List A due to unique / different permissions
• The lookup fields need to stay lookup fields and can not be transformed into single line of text fields.
• Due to the fact that the fields are of type lookup, I can't concatenate them with a simple calculated column.
• The solution must be sandboxed and not farm. We aren't allowed to deploy dlls, only .wsp

Problem: What I would need is a sandboxed custom workflow activity that triggers on List B item added/changed. When triggered, activity grabs the State and City values from the item in list B, goes to List A and searches for a combination of the same State and City. When found, it grabs the associated population. Lastly it multiplies the population by the % from "Affecting % of population" and pastes that result into the "Population Affected" field.

Bonus: At some point, I will also need a sandboxed custom workflow activity that triggers on List A item changed (the population field). When the population for specific State+City combination changes, the activity would go to List B and update all "Population Affected" fields that satisfy the same State+City for all companies (multiple rows).

Thanks in advance!

Answer 1

What you need is an event receiver. Nothing you've stated above leads me to believe you need a workflow. Look over my blog to see your options:

http://mattbramer.blogspot.com/2012/11/binding-event-handlers-to-sharepoint.html