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Parameters:
objectId: Id of the parent object. You can use 15-character or 18-character Salesforce.com id. For example, this ID is the ID of the case record if the attachments are being uploaded for a case.
attachments:List of Salesforce SObject for uploading. The SObject will be representing the "File" object. For example, for a Case attachment, the SObject will be representing the cg_CaseFile_c record.
policyMap: Map of policy conditions and theirs values that represent the additional policy parameters used during upload (e.g. ('$Content-Disposition', 'attachment; filename)). For more information, visit the Amazon documentation:
http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html
Return Value: The method will return the list of UploadRequestInfo (Figure 7see table below), which holds information about the files that are about to be uploaded.
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