How to cascade changes to a child?

[Becky McNichols]

I have a set with a one-to-many relationship. Parent="salesheader", child="treatments". The link is a field called "T19G_No" and both are indexed on that field. In the set definition the "cascade changes/deletes" is marked.

There are 2 fields which, when I change their values in the parent, I'd like them to automaticlly have them change in the child. Here are the fields and their field rules:

Salesheader-date (D,8,0):simple default expression: DATE()

Treatments-date (D,8,0): simple default expression:
LOOKUPD("F",T19G_No,"Date","Salesheader.dbf","T19G_No")

Salesheader-T19G_No (C,8,0): Date entry: always required
simple default expression: STR(PREVIOUS("T19G_No"))+1
validation: value of field must be unique

Treatments-T19G_No (C,8,0): no field rules defined (this is the linking field)

I have used the default expressions because I want the user to be able to have the option to overwrite a default value.
The field rules work fine as I am entering data, but if I change a date or T19G no.on a record which has already been saved, they do not change in the child (treatments), which makes some of my reporting inaccurate.

How can I go about achieving this? I thought the "Cascade changes/deletes" would do this - obviously not! Thanks for any help.

[Jim Chapman]

RE: How to cascade changes to a child?

Hi Becky,

Cascading changes/deletes will, of course cascade deletes, but changes only cascade when the changes are to the linking fields.

A default expression only defaults to the value when a record is written, not when it is changed. A default expression will also allow the user to overwrite the default with a user entered value. You could make the expression calculated, but then a user could not override it. Probably the easiest way to do this is to create a script that is played on a field event, such as the Canchange event, or a record event. This script would contain the logic needed and based on the outcome, rewrite the value/s in the child fields.

Good luck,

Jim

[Tom Cone Jr]

RE: How to cascade changes to a child?

The user's guide does a decent job of discussing referential integrity within the context of set design. The 'cascade changes/deletes' feature is limited to the linking field and is designed to maintain the link between related records in the child and parent tables, when the user changes the value of the link field in the parent table.

Assuming the fields of interest to you are not the linking field then cascade changes/deletes won't help... as you've already discovered.

There are several ways to accomplish what you are after.

For instance you could define an update operation to change the values in all child table records that have the same link field value, using the current values in the fields of interest to supply the new values in the selected child table records. i.e. filter the child table on the current link field value. Then update the fields of interest in the child to match the field values in the parent. Figuring out the right interface for this might be tricky. If you want it to be transparent, then your code will have to detect when a field value in the parent changes, and then call the update operation silently.

-- tom

[Becky McNichols]

RE: How to cascade changes to a child?

Thanks Jim & Tom-
I was sure hoping that there was something I could easily define in the set structure or field rules. Wishful thinking! Thanks for your advise.