I work on the edit form of an external list. I can pick items from an associated content type with a picker. There is the option to "Check if item exists", but currently it only accepts IDs. Can I change this checker to accept different properties, and how?
If you try to check an item by something other than the ID, the ReadList operation of the associated item is used. (In case of IDs it seems to be the ReadItem operation.) You need to implement a wildcard filter against the property you want to search after in the checker, which also enables the search field in the picker.