How to defer the mandatory constraint?

The mandatory validation is a database constraint and you do not have any control over it in ADF. You will not have the validation execution tab for these kind of DB constraint validation if you want to defer it based on some condition.But the Error message can be overridden.

if you want to populate the key attribute for the child from the parent then enable “Composite Association -> Cascade Update Key Attributes” for the association

JBO-27024: Failed to validate a row with key oracle.jbo.Key usually occurs

1. Not providing value for a mandatory attribute.
2. Incorrect value for an attribute of different data type
3. any of your other validation rules failed.

the validation is failing because the id attribute may not be getting created properly. Because of this it could not validate the row as the id is null. row.validateEntity() will help to identify the error by calling it when you commit the record and check where exactly the error pops up.

4. when the primary key is not based on a sequence and depends on the composite. The solution is to create a surrogate key. If you want to override the db constraint you must have a surrogate key populated programmatic way every time a new row is created. So that the data is unique all the time and proceed with a customized error message for each attribute, make the surrogate key hidden and read only.

if you want to suppress the validation then use skipValidation=true in pageDef or have the immediate set to true.