this is very simple to develop. There are actually many controls that already use this principle. Like you've correctly pointed out, my sample with Image galleries is one of them.
Here is the high level overview of the steps you would need to perform to achieve desired functionality:
1. Add new command and view to your module. Let's call this view and command "Customer info"
2. In this view provide User interface (form) and functionality for managing customer info (e.g. customer name, address, phone number, id and so on)
4. Add meta field named CustomerID to the GC module for which this functionality will be implemented
3. Create a new control which will implement ITextControl interface. Set it's ID to "CustomerID" (same as the key of meta field). In this control provide drop down list from which user can choose a customer (drop down list will be bound to the data managed by the UI created in step 2)
4. For the mandated Text property of ITextControl use id of the customer.
5. Now you have the id of the associated customer with each content and will be able to easily pull all additional data you may need.
I hope this helps. Let us know if there is anything else we can do for you.
the Telerik team
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