Hi Michael,
The data model of SMW never considered "insertion order" as a piece of
information that should be recorded. In fact, a normal SQL RDBMs like
MariaDB has no obligation to return tuples in a specific order unless
there is an ordering clause in the query. Same for SPARQL. Relying on
result orders to be the same "as in the table" is generally not robust.
To store and retrieve ordered lists in SMW, there are several options:
(1) Use sub-objects instead of plain values and store the index of each
entry with the value. Then sort by this value when retrieving data.
(2) Store the unordered values as you do now, and in addition store a
string of the ordered values (comma-separated) in another property. You
can use page variables to build such a string and #arraymap to decompose
it (if you want to do more than just display this string).
I have worked with both solutions in practice. For things like lecture
dates, we use (1) (though we use the date rather than the insertion
order as an ordering criterion there). For things like author lists
(where order matters), we use (2).
Best regards,
Markus
On 24/09/2020 12:37, Michael Erdmann wrote:
Dear Community,
is there a way to maintain the order of attribute values, e.g. in ASK
queries. By "maintain" I mean to keep the order of the values as they
had been added in the wiki page's annotations.
Currently I get this:
Test_Page contains:
[[MyProperty::Page1]]
[[MyProperty::Page2]]
[[MyProperty::Page3]]
Another_Page contains this query:
{{#ask: [[Test_Page]] | ?MyProperty | format = ul }}
and shows this result
Test_Page (MyProperty: Page1, Page2, Page3)
Changing the order in Test_Page to:
[[MyProperty::Page2]]
[[MyProperty::Page3]]
[[MyProperty::Page1]]
still results in exactly the same query result, i.e. Page1 at the
beginnig of the list.
Is there a way to accomplish what I want in Wiki text?
If there is a way to accomplish this in PHP that is also fine for me. I
investigated a bit already and found, that
$data = StoreFactory::getStore()->getSemanticData( $myPage );
$values = $data->getPropertyValues( $myProperty );
already returns the values in a constant order (page-IDs?). Is the DB
maybe not prepared to maintain this information?
BTW. I am using MW1.31 and SMW3.0.2.
THX,
michael
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