If you have grails errors message:
Grails No row with the given identifier exists: [Category#0]
it means that data consistency of your app is broken.
First you need to decipher the message. It says that you have class named Category and you are trying to reference an object with id - 0 . Since this row with id doesn't exist you get this error.
Next you need to find where and who is trying to get information about this object. This can be done by checking the stack trace of the application.
... 39 common frames omitted
As you can see it's called from BookController line 30. So most probably while searching for Book you get this error ( better to check the code).
- Last step is to fix currupted data by:
- add this information in table Category
- update reference table - Book and the field which points to Category with appropriate value