Every where we can use the record over the cdt. what is use of cdt over record? where can we use cdt instead of Record?
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Records allow you to connect data from different sources just like foreign keys and have a unified place for your users to work on.
Here is a quick explainer video - https://www.youtube.com/watch?v=YjxuSn5bc48&ab_channel=AppianCommunity
Why you should avoid using CDTs whenever possible - https://appianspace.com/2022/08/16/appian-is-killing-cdts/
Cases when you should choose CDT over records
You should be prioritizing Synced Records most of the time.
Here's why: https://docs.appian.com/suite/help/23.4/records-data-sync.html
Only reason to use a CDT when you need something a little more strongly typed than a map. CDTs can sometimes be useful inside Process Reports too.