I'm trying to import a combined fully mapped CSV file on a Salesforce non-profit package with Data Import Wizard you know that we focus on 3 objects in this case : (households(account) , Donors(contact) and Opportunities(Donations) I want to know if there is a solution that every time we upload the CSV file , it doesn't create new contacts and households can anyone help?
Before you load the data, need to understand the relationship among those objects.
Opportunity is related to Account with M-D relationship.
Contact is related to Account with Lookup relationship.
Before importing Opportunity, Account must exist in the system, otherwise you will get error during upload.
If Account record exist then you can directly point to the AccountId and load the Opportunities.
If you already have Account and Contact, and you need to insert only the Opportunity then use DataLoader and upload the data.
Refer Import Data trailhead and video for further information.