Robert Jan van der Waals

And just to be clear, internally Data Crow uses unique IDs which are not visible in the UI by default. So the data model, regardless of the key field setting, does not change.

Yes, use the Settings > General Field Settings (https://datacrow.org/docs/configuring-data-crow/#fieldsettings). Basically when you created the field you supplied the initial settings for it, but yes, these can be changed after the fact. There's the possibility that you change the key field settings to fields which is, at the moment, not unique for every item. Every time you update (or create of course) an item though, the system will check and enforce your newly selected key field setting.

Unfortunately not, no. There is no option to change this. I think your requirement is clear but to be honest a bit niche for a generic book module.

Hi, that is weird. Can you check in the Item Form Settings? You can removed a filed from any of the tabs and reassign it to the tab you like.

Good idea; logged https://sourceforge.net/p/datacrow/tickets/165/

Feature Request: Comments for Loan(s)

You have multiple options :-) If this is essentially the same book, you can use editions; you then have one book with 2 editions for example. Simply right-click the current item and choose "Copy Book & Assign as Edition". But I suspect this is not the case for you; If this is another book entirely, change the field setting so that a combination of fields make the book unique. Settings > General Field Settings ---> tick the "Key" checkbox for one or more additional fields beside the currently selected...

Sorry to hear about your issue. So I assume you have Data Crow installed without a username and password? And you then opened the Synchronization Service? What was the error message you got when you initially connected? There might be a clue, hopefully, in the Data Crow log (CTRL-L). Anyway, when you retry open the app, do you have the synchronization service open and started? I think it failed to connect and it is now actively retrying but it has gone into a bit of a loop. If you can get it to go...