By default, when using our Relational Data Feature, Flatfile will upsert data from the child sheet into the parent sheet. If you would prefer that the parent sheet not be modified, you can disable this ability with an option placed on the field in the child sheet that should not upsert to its parent.
When you are deploying your sheets using the Flatfile Platform SDK, you can add this as an option to your LinkedField field types. The syntax for this would be
upsert: false. For more information about the options available for LinkedFields or for deploying via the Platform SDK, visit our developer docs.
When this option is added and set to false, any records in the linked field that aren't present on the parent template will not be added to the parent, and instead will display an error in the child sheet to indicate that the field must be matched to a value that is present in the parent sheet. If this option is not included on your sheet, the default behavior will be to upsert data.