Insertions into Zipper trees on XML files in Clojure

clojure, clojure-contrib, xml

Solution

Firstly, you should use `:content` (and not `:contents`) in your definition of Fred.

With that change in place, the following seems to work:

(-> (zf/xml-> @db :item) ; a convenient way to get to the :item zipper locs
    first                ; but we actually need just one
    zip/rightmost        ; let's move to the rightmost sibling of the first :item
                         ; (which is the last :item in this case)
    (zip/insert-right fred-item) ; insert Fred to the right
    zip/root)            ; get the modified XML map,
                         ; which is the root of the modified zipper

Your `append-item2` is very similar, there are just two corrections to make:

`zf/xml->` returns a sequence of zipper locs; `zip/rightmost` accepts just one, so you have to fish one out first (hence the `first` in the above);

after you're done modifying the zipper, you need to use `zip/root` to get back at (the modified version of) the underlying tree.

As a final note on style, `print` + `format` = `printf`. :-)

Problem

I'm confused as how to idiomatically change a xml tree accessed through clojure.contrib's zip-filter.xml. Should be trying to do this at all, or is there a better way? Say that I have some dummy xml file "itemdb.xml" like this: ``` <itemlist> <item id="1"> <name>John</name> <desc>Works near here.</desc> </item> <item id="2"> <name>Sally</name> <desc>Owner of pet store.</desc> </item> </itemlist> ``` And I have some code: ``` (require '[clojure.zip :as zip] '[clojure.contrib.duck-streams :as ds] '[clojure.contrib.lazy-xml :as lxml] '[clojure.contrib.zip-filter.xml :as zf]) (def db (ref (zip/xml-zip (lxml/parse-trim (java.io.File. "itemdb.xml"))))) ;; Test that we can traverse and parse. (doall (map #(print (format "%10s: %s\n" (apply str (zf/xml-> % :name zf/text)) (apply str (zf/xml-> % :desc zf/text)))) (zf/xml-> @db :item))) ;; I assume something like this is needed to make the xml tags (defn create-item [name desc] {:tag :item :attrs {:id "3"} :contents (list {:tag :name :attrs {} :contents (list name)} {:tag :desc :attrs {} :contents (list desc)})}) (def fred-item (create-item "Fred" "Green-haired astrophysicist.")) ;; This disturbs the structure somehow (defn append-item [xmldb item] (zip/insert-right (-> xmldb zip/down zip/rightmost) item)) ;; I want to do something more like this (defn append-item2 [xmldb item] (zip/insert-right (zip/rightmost (zf/xml-> xmldb :item)) item)) (dosync (alter db append-item2 fred-item)) ;; Save this simple xml file with some added stuff. (ds/spit "appended-itemdb.xml" (with-out-str (lxml/emit (zip/root @db) :pad true))) ``` I am unclear about how to use the clojure.zip functions appropriately in this case, and how that interacts with zip-filter. If you spot anything particularly weird in this small example, please point it out.

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