johnf wrote:
> On Sunday 31 December 2006 06:08, Paul McNett wrote:
>> Carl Karsten wrote:
>>> Much like I want the database engine to make sure I don't create orphan
>>> child records, I want some low level generic code that makes sure
>>> database updates don't get overridden. I doubt I am the only one.
>> I agree with you, Carl, that Dabo should provide some basic behavior for
>> detecting and responding to collisions. Then, the application developer
>> can decide to override, circumvent, or expand on the basic behavior Dabo
>> provides.
>>
>> Adding the list of fields to the where clause seems like a pretty smart,
>> generic way to accomplish this. VFP got a lot of things right, and this
>> is one of them. I don't see why it wouldn't work with all backends, and
>> anyway the app developer can set it to not detect but overwrite updates
>> if they choose.
>
> Let be get this right. If I have a 100 field table and I want to change one
> field the update statement will look something like this:
> Update table set myfield = "something" where 99 fields = 99 fields???
>
close.
First, there are 5 Types (VFP only used 4, your example just made me realize
there is a 5th.)
So as the developer, you get to pick one. your example is closes to the 5th:
"PK and All Fields" (which is the same as All Fields) so we will use it.
The WHERE will include the modified field too, and in keeping with the
Description will start with the PK:
Update table set myfield = "something" where
PKField = PKvalue and
myfield = myfield_old_value and
98 fields = 98 values
all 100 fields accounted for.
> This will insure that the fields I didn't change were not changed? Do I have
> it right?
You probably also want to insure the field you are changing didn't change.
"If someone else changes any of these fields, the WhereClause will not be true
anymore, and so no records will be updated."
http://fox.wikis.com/wc.dll?Wiki~VfpViews~VFP
It makes much more sense once you understand it :)
If you can figure out a better way of wording it, please do.
I think the concept of "target record" or "active record" or "the record we are
interested in" needs to be better defined. I wouldn't want anyone to think
there was a record pointer, but the concept is similar (if you squint.)
Carl K
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