I created a custom table with additional settings for customers. Next I added a field to the customer core table in which I'd like to store the id choice per customer. I extended with EntityExtensionInterface to the class which holds the custom table definition, storagename for this field is customer_setting, propertyName is customerSetting, and referenceField is id.
When I manually store an id from this custom table, with certain settings, I can retrieve and use these settings in the storefront.
For the backend I created a single select to the entity custom_table, with using v-model='customer.extensions.customerSetting.id' the manually 'injected' id from the custom table, this choice gets a 'Vee' indicating this is selected. Changing to another id and saving results in an error: Customer could not be saved. Also when no value is 'injected' into the added field from the customer table, the object (?) customer.extensions.customerSetting does not exist, and thus with v-model='customer.extensions.customerSetting.id' the result is an error for the single-select box I try to construct. It is obvious I am missing something, but I have no clue, can anyone elucidate?