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We can upsert(Insert/Update) records using External Id field in Salesforce.
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1. Use the following link to setup Connected App to get Access Token.
2. We can do a PATCH Request to do the Upsert operation.
Endpoint URL:
https://{Salesforce My Domain UR}/services/data/v59.0/sobjects/{Object API Name}/{External Id Field API Name}/{External Id Field Value}/
Request Header:
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Request Body:
{
"Description" : "Sample Testing"
}
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