Following this question (not essential for understanding) CakePHP hasOne-belongsTo relationship, how to look up and insert foreign key from user input?
To add a property, the Property.postcode field is taken, used to find a matching Postcode.postcode, and then the Property.postcode_id (foreign key for postcode) is set for saving. Property.postcode is for user input only, it is not saved.
To edit, the system should be the same - postcode entered is checked against the Postcode table records. However, this presented an empty field on the edit view, as Property.postcode doesn't exist in the DB, it's just for data entry.
How can I populate the Property.postcode field with the Postcode.postcode value in the edit view?