Security in sql filters

I'm creating a site that is a directory of stores that users can search for. I want to use the built-in login and membership portal so that store representatives can login and update information on their stores. I will have one account per store. I'd like to keep all of the store data in a sql database that I'm creating.

 

When the store manager logs in to update info about his store, how can I return a gridview allowing him to update and view JUST HIS/HER stores info in a secure way?
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