On 12-10-2022 18:21, Michael Van Canneyt via lazarus wrote:
On Wed, 12 Oct 2022, nibbikfrans via lazarus wrote:
Hi,
I have a collection stored in a file. One property of each
collectionitem is a value of what seeems to be a set but is not. That
property is no longer needed. Is there a way to delete that property?
I suppose I can do that by creating a new collectionitem type without
that property and migrate the data. But then a have a different
collection which meens a have to make lots of changes.
Yet that is the only correct way.
If you can make a descendent, you can
override the property and simply discard the value when it is set in the
setter.
What you also can do is remove the property and override the
DefineProperties method of your CollectionItem object and add a dummy
reader for your propertyname. This way you will be able to read old data
and in new data it won't get written.
I didn't test this on FPC, but I've done it this way several times in
Delphi.
Marc
If deleting a property isn't possible, how can I delete the value of
that property?
In the file, in the instance of the collectionitem or where ?
And an extra question is: how can I test whether the property has a
value or not?
The possible value is defined as followes:
TTest = (test1, test2, test3);
TTestValues = set ot TTest;
The property has a set as value ?
If the set is empty, then the property has no value ? Unless empty value
is also a value.
Michael.
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