As I promised, I created an open source library for this stuff: https://github.com/netizer/relational_mapper
More info here: https://groups.google.com/forum/#!searchin/clojure/krzysiek/clojure/g6Yxk-o6_rQ/uo9IVN20CAAJ Enjoy :-) Krzysiek Heród On Tuesday, May 26, 2015 at 4:43:18 AM UTC+8, Krzysiek Herod wrote: > > Thanks Daniel, and Sean for your answers. > > Daniel, the part that interests me the most is "converting resultset rows > to collection (of objects)", and I think a lot of people do just what you > said (own customized function). I was looking for, and will probably in the > end implement an open source library that does exactly that in some > standardized way. > > Sean, maybe my use case is specific to web applications. In REST API's > it's common to respond with something like "Example Result" here: > https://dev.twitter.com/rest/reference/get/statuses/mentions_timeline I > completely agree with you about ORMs, but in case of REST API's one just > needs to somehow map the queryset to a structure of hashes and arrays (not > necessarily objects), and this task is much heavier than I thought in the > beginning, from choosing between making many queries to fill in the hash of > related objects vs making JOINs, to complexity of extracting data from a > set of rows with potential repetitions, rows of null values (like Daniel > said happens for instance in case of LEFT JOINS), and different kinds of > relations (has-one, has-many, belongs-to). > > I just thought that maybe a tool for that (relational mapper - but not > "object-" like it's common in Java, and Ruby, but just hashes and arrays) > already exists, but if not, I'll implement it and open source it soonish. > BTW, if there are here developers that would be interested in such tool, > let me know what data format and a set of features would you find the most > desirable. > > > > W dniu poniedziałek, 25 maja 2015 19:13:10 UTC+2 użytkownik Sean Corfield > napisał: >> >> I just don’t consider it a problem. A query returns a flat result set — a >> sequence of hash-maps. That’s it. That’s what SQL returns (essentially a >> table) and it’s a perfectly reasonable data structure for Clojure to work >> with. >> >> The JOINs in SQL just say how to link tables together to produce that >> (flat) result set. Any structural grouping semantics you want to apply are >> up to your application. >> >> FWIW, I find ORMs — which is where you’re going with this — to be far >> more trouble than they’re worth and I just don’t see the benefit in Clojure >> which is all about pure data structures. I worked with a lot of ORMs — and >> written several of my own — over the last couple of decades and these days >> I just avoid them. >> >> Sean >> >> On May 24, 2015, at 3:10 AM, Krzysiek Herod <krzysie...@gmail.com> wrote: >> >> It seems to me that it's a problem that sooner or later appears in any >> project using relational database (apart form easy cases, when there is no >> many relations between tables). Am I missing something? How do you guys >> work with database results of queries containing several tables referring >> to each other? >> >> W dniu czwartek, 21 maja 2015 21:57:03 UTC+2 użytkownik Krzysiek Herod >> napisał: >>> >>> I've found the question appearing here, but a long time ago, so I >>> thought that maybe the situation changed: >>> >>> Is there a relational mapper in clojure (or in java) that takes query >>> result and generates an array of hashmaps? >>> I mean something that converts the result of this query: >>> "SELECT * FROM posts LEFT JOIN comments ON (comments.post_id = posts.id) >>> LEFT JOIN users ON (posts.user_id = users.id)" >>> into (for example) the following structure: >>> [{:title "Post title" :user {:first_name "User 1"} :comments [{:title >>> "Comment 1"} {:title "Comment 2"}]}] >>> >>> I've used kormadb for that, but it works like this only with has-many >>> relation (belongs-to puts all of the fields from related tables into the >>> same hash as if it was one table, and using "with" do not solve the problem >>> neither). >>> >>> Is there any other clojure library that does that, or is any java >>> library used instead? >>> >> >> >> -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
