Way to specify field as read-only (do not insert)?

[sparkertime]

I have a field whose value must be generated by the DB at insertion time by calling a Postgres function. I have defined the column as extern_id varchar(10) NOT NULL DEFAULT next_extern_id() I would like the application to read the value of this field, however.

I have tried both :read_after_write and :autogenerate on my field definitions but unfortunately they still try to pass an explicitly null value for this column. Is there a way to specify this field should not be part of any INSERT or UPDATE statement, but should be part of a RETURNING clause?

[josevalim]

:read_after_writes only reads the column back after writes, it still does not change the value sent. To avoid sending values, you can define a callback that removes the changes from the changeset:

before_insert Ecto.Changeset, :delete_change, [:extern_id]
before_update Ecto.Changeset, :delete_change, [:extern_id]

This way the value will never be sent to the database and, with read_after_writes, the proper one will be read back.

[sparkertime]

@josevalim Thanks, I didn't think of that. What does the recent deprecation of :read_after_writes mean for this? Is it safe to assume that if it every truly goes away, I'll have some other means of accomplishing this kind of behavior in Ecto?

[josevalim]

It is very likely we can't really deprecate it... so it will stay. I do want to push towards autogenerate in the next release though.