Alexander Burger <[email protected]> writes:
Hi Alex,
>> assume I have a (hypothetical) database with objects of class +Thing
>> that have relations defined like this:
>>
>> #+name: myBag
>> #+BEGIN_SRC picolisp
>> (rel stamp (+Bag)
>> ((+Symbol)) # timestamp-type
>> ((+Ref +Date)) # start date
>> ((+Time)) ) # start time
>> #+END_SRC
>>
>> e.g.
>>
>> ,--------------------------
>> | stamp (active 735458 NIL)
>> `--------------------------
>>
>> #+name: myListBag
>> #+BEGIN_SRC picolisp
>> (rel props (+List +Bag)
>> ((+Ref +String)) # Key
>> ((+String)) ) # Value
>> #+END_SRC
>>
>> e.g.
>>
>> ,--------------------------------------------------------
>> | props (("key1" "val1") ("key2" "val2") ("key3" "val3"))
>> `--------------------------------------------------------
>>
>> #+name: myStringList
>> #+BEGIN_SRC picolisp
>> (rel tags (+List +Ref +String))
>> #+END_SRC
>>
>> e.g.
>>
>> ,----------------------------
>> | tags ("tag1" "tag2" "tag3")
>> `----------------------------
>>
>>
>> Now, how can I query the DB from a program, using these relations? E.g.
>>
>> 1. Find objects with an active (time)stamp with date 735458?
>> 2. Find objects with props with key 'key1' and value 'val1' or 'val2'
>> for this key?
>> 3. Find objects with tags 'tag1' and 'tag3'?
>
>
> The simplest is using 'collect' (not tested):
>
> (collect 'stamp '+Thing 735458)
>
> (filter
> '((This)
> (find
> '((L)
> (and
> (= "key1" (car L))
> (member (cadr L) '("val1" "val2")) ) ) )
> (: props) )
> (collect 'props '+Thing "key1") )
>
> (sect
> (collect 'tags '+Thing "tag1")
> (collect 'tags '+Thing "tag2") )
Ok, so I use Lisp and not Pilog.
This looks good and reasonably simple - thanks! I have to try ...
PS
I did not know about the 'sect' function, definitely useful.
--
cheers,
Thorsten
--
UNSUBSCRIBE: mailto:[email protected]?subject=Unsubscribe
