Thanks for the reply! That makes sense, I knew it must have something to do with the b-tree index structure, but have just been following examples and language reference. 'collect and 'select are definitely more appropriate for the exploration I am doing (though I am also curious about the low level stuff too)
If you don't mind, I am still having a bit of trouble figuring out if my E/R models are correct, and also if I'm creating objects in the right way. Here's what I have so far, I'd appreciate any comments or hints! Thank you! (class +User +Entity) (rel nr (+Need +Key +Number)) (rel name (+Need +Idx +String)) (rel memberships (+List +Joint) user (+Membership)) (class +Group +Entity) (rel name (+Need +Idx +String)) (rel memberships (+List +Joint) group (+Membership)) (class +Membership +Entity) (rel role (+Need +Ref +String)) (rel user (+Joint) id (+User)) (rel group (+Joint) name (+Group)) (obj ((+User) nr 1) name "Grant") (obj ((+Group name "Go Club"))) (commit) (obj ((+Membership) role "Organizer") user (db 'nr '+User 1) group (db 'name '+Group "Go Club")) (commit) Grant Sent with ProtonMail Secure Email. ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Sunday, May 19, 2019 12:40 AM, Alexander Burger <a...@software-lab.de> wrote: > Hi Grant, > > welcome here :) > > > My name is Grant and I'm just getting started with picolisp. I'm trying an > > exercise to model user-groups and memberships with the Entity/Relation > > database. > > I must be misunderstanding something, or doing something strange because I > > can't seem to create/retrieve items the way I expect to. For example: > > I think you did everything perfectly right. > > But 'iter' is a rather low-level function. If you call it as > > > (iter (tree 'name '+User) '((This) (println (: name)))) > > it printsall entries in the b-tree. As your 'name' relation is an '+Idx', it > creates several entries per value. > > If you want to iterate only the primary entries, you can pass a boolean 5th > argument to 'iter': > > (iter (tree 'name '+User) > '((This) (println (: name))) > NIL > T > T ) > > Or use one of the higher-level functions which know about the relations and > handle them properly > > (collect 'name '+User) > (collect 'name '+User NIL T 'name) > > In interactive mode you can also just > > (select +User) > (select +User name "Grant") > (select nr name memberships +User name "Grant") > > ☺/ A!ex > > ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > > UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe -- UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe
