I tried to follow the documentation for clojure.instant/read-instant-timestamp, which reads:
clojure.instant/read-instant-timestamp
To read an instant as a java.sql.Timestamp, bind *data-readers* to a
map with this var as the value for the 'inst key. Timestamp preserves
fractional seconds with nanosecond precision. The timezone offset will
be used to convert into UTC.`
The following result was unexpected:
(do
(require '[clojure.edn :as edn])
(require '[clojure.instant :refer [read-instant-timestamp]])
(let [instant "#inst \"1970-01-01T00:00:09.999-00:00\""
reader-map {'inst #'read-instant-timestamp}]
;; This binding is not appearing to do anything.
(binding [*data-readers* reader-map]
;; prints java.util.Date -- unexpected
(->> instant edn/read-string class println)
;; prints java.sql.Timestamp -- as desired
(->> instant (edn/read-string {:readers reader-map}) class println))))
How can I use the *data-readers* binding? Clojure version 1.5.1.
clojure.edn functions by default only use data readers stored in clojure.core/default-data-readers which, as of Clojure 1.5.1, provides readers for instant and UUID literals. If you want to use custom readers, you can do that by passing in a :readers option; in particular, you can pass in *data-readers*. This is documented in the docstring for clojure.edn/read (the docstring for clojure.edn/read-string refers to that for read).
Here are some examples:
(require '[clojure.edn :as edn])
;; instant literals work out of the box:
(edn/read-string "#inst \"2013-06-08T01:00:00Z\"")
;= #inst "2013-06-08T01:00:00.000-00:00"
;; custom literals can be passed in in the opts map:
(edn/read-string {:readers {'foo identity}} "#foo :asdf")
;= :asdf
;; use current binding of *data-readers*
(edn/read-string {:readers *data-readers*} "...")
(The following section added in response to comments made by Richard Möhn in this GitHub issue's comment thread. The immediate question there is whether it is appropriate for a reader function to call eval on the data passed in. I am not affiliated with the project in question; please see the ticket for details, as well as Richard's comments on the present answer.)
It is worth adding that *data-readers* is implicitly populated from any data_readers.{clj,cljc} files that Clojure finds at the root of the classpath at startup time. This can be convenient (it allows one to use custom tagged literals in Clojure source code and at the REPL), but it does mean that new data readers may appear in there with a change to a single dependency. Using an explicitly constructed reader map with clojure.edn is a simple way to avoid surprises (which could be particularly nasty when dealing with untrusted input).
(Note that the implicit loading process does not result in any code being loaded immediately, or even when a tag mentioned in *data-readers* is first encountered; the process which populates *data-readers* creates empty namespaces with unbound Vars as placeholders, and to actually use those readers one still has to require the relevant namespaces in user code.)
The *data-readers* dynamic var seems to apply to the read-string and read functions from clojure.core only.
(require '[clojure.instant :refer [read-instant-timestamp]])
(let [instant "#inst \"1970-01-01T00:00:09.999-00:00\""
reader-map {'inst #'read-instant-timestamp}]
;; This will read a java.util.Date
(->> instant read-string class println)
;; This will read a java.sql.Timestamp
(binding [*data-readers* reader-map]
(->> instant read-string class println)))
Browsing through the source code for clojure.edn reader here, I couldn't find anything that would indicate that the same *data-readers* var is used at all there.
clojure.core's functions read and read-string use LispReader (which uses the value from *data-readers*), while the functions from clojure.edn use the EdnReader.
This edn library is relatively new in Clojure so that might be the reason why the documentation string is not specific enough regarding edn vs. core reader, which can cause this kind of confusion.
Hope it helps.
Related
I just finished my first six weeks working with Clojure and so far I'm pretty happy with the language. I'm developing my personal blog with leiningen and PostgreSQL. I already can publish new content, upload files and I have sessions, cookies and roles, anyway I think at this point I have enough code to start to worry about the testing section, but I'm kind of stuck since looks like a lot of things are happening in the clojure's testing and spec side.
So I have this function:
(defn download
"GET /admin/uploads/download/:id"
[params]
(let [id (-> params :id)
upload (model-upload/get-upload id)
filename (:filename upload)
body (clojure.java.io/file (str "public/uploads/" filename))]
{:status 200
:body body
:headers {"Content-Type" "application/pdf"
"Content-Length" (str (.length body))
"Cache-Control" "no-cache"
"Content-Disposition" (str "attachment; filename=" filename)}}))
The function takes a map as argument and delivers a final map to be sent and processed by compojure. I come from a Rails world so the way to test this function in Rails would be to create a FactoryGirl class, create a Rspec model file with the classic:
expect(first_map).to eq(map_returned_by_function)
in it comparing what is expected, and then to run the rspec from the command line to get the green or red line.
Since yesterday I'm trying to replicate that process with Clojure using this doc:
https://www.codesai.com/2018/03/kata-generating-bingo-cards
but I think there is not yet a "standard" way to do a test including the DB (CRUD) part in Clojure. I don't even know where to put the spec files. I see Clojure libraries similar to FactoryGirl but I don't know if I should create my own data structures with spec so I'm not sure where to start, there are clojure.test.check.generators and spec generators but I don't know if they are different or if I should use only spec but not clojure.test.check. Can I run a test from the command line and not inside the REPL?
I mean: is there a document or tutorial about how to test a set of CRUD functions? I think I just need the initial HOWTO and then I could take it from there and I'll write a tutorial to newbies like me.
UPDATED:
It looks like Midje is what I'm looking for:
https://github.com/marick/Midje/wiki/A-tutorial-introduction
It's idiomatic in Clojure to push IO to the edges of your application. Instead of reading from the DB inside your download function, you pass in the data read from the DB into your download function in the param map. Then you write your tests against the pure part.
Your function would end up looking like this:
(defn download-without-db
"GET /admin/uploads/download/:id"
[params]
(let [upload (-> params :upload)
filename (:filename upload)
body (clojure.java.io/file (str "public/uploads/" filename))]
{:status 200
:body body
:headers {"Content-Type" "application/pdf"
"Content-Length" (str (.length body))
"Cache-Control" "no-cache"
"Content-Disposition" (str "attachment; filename=" filename)}}))
(defn get-upload-from-db [params]
(assoc params :upload (-> params :id model-upload/get-upload)))
(defn download [params]
(-> params
get-upload-from-db
download-without-db))
You're just looking for clojure.test. It even mentions relationships with RSpec in its doc.
This is included as part of Clojure itself, no dependencies are needed, and I'd recommend you get familiar with it first before using a non standard test framework like Midje, since it is the defacto test framework for Clojure, and the most popular one.
You would write a test as such:
(deftest download
(testing "With valid input"
(testing "it should return a header map with filename included"
(is (= first_map (unit/download {:id 1}))))))
Now, Clojure is not object oriented, so there are no objects to mock. That said, you often use Java form within Clojure, and Java provides classes and objects. If you want to mock them easily, you can use the Java mocking framework called Mockito.
In your case though, the download function does not use any Java objects. So you don't need too.
Now, if you want this to be an integration test, the test I wrote is good enough for you. If you want this to be a unit test, and I assume (model-upload/get-upload id) does some IO, you'll want to mock the model-upload/get-upload function. You can easily do this using with-redefs-fn:
(deftest download
(testing "With valid input"
(testing "it should return a header map with filename included"
(with-redefs-fn {#'model-upload/get-upload (constantly {:filename "cool.pdf"})}
(is (= first_map (unit/download {:id 1})))))))
Or you can use with-redefs:
(deftest download
(with-redefs [model-upload/get-upload (constantly {:filename "cool.pdf"})]
(testing "With valid input"
(testing "it should return a header map with filename included"
(is (= first_map (unit/download {:id 1})))))))
Here are some online resources for you:
http://jafingerhut.github.io/cheatsheet/clojuredocs/cheatsheet-tiptip-cdocs-summary.html
http://clojuredocs.org/
http://clojure-doc.org/
https://www.braveclojure.com/
https://pragprog.com/book/dswdcloj2/web-development-with-clojure-second-edition
and the following is an example of how I like to structure general tests (not CRUD, though):
https://github.com/cloojure/tupelo/blob/master/test/tst/tupelo/misc.cljc
I am new to Clojure and Reagent. Kindly tell how to print the variable first inside the atom variable contacts?
(def app-state
(r/atom
{:contacts [{:first "Ben" :last "Lem" :middle "Ab"}]}))
First of all: the reagent tutorial is a really good place to start. It even gives you examples to solve exactly this problem.
Since reagents atom can be treated just as a regular Clojurescript atom, you can use all your normal sequence operations. Keep in mind that in order to access the current value, you have to dereference the atom via #.If you really just want to access the first :first in your atom:
(:first (first (:contacts #app-state))) or (get (first (get #app-state :contacts)) :first)
Or, if you think it's more readable
(-> #app-state
:contacts
first
:first)
I guess what you might want to do is define a few functions to make the access more easy such as:
(defn get-contacts!
"Returns the current vector of contacts stored in the app-state."
[]
(:contacts #app-state))
(defn get-first-names!
"Return a vector of all first names in the current list of contacts in the
app-state."
[]
(mapv :first (get-contacts!)))
Please keep in mind that in reagent (and in general really) you might want to dereference that atom as fiew times as possible, so look for a good place to dereference it and just use regular functions that operate on a simple sequence instead of an atom.
Still, I would really suggest you go read the aforementioned reagent tutorial.
Here is a concise way to access the value that you are looking for using Clojure's (get-in m ks) function:
(get-in #app-state [:contacts 0 :first])
Just as an extra, you may see this often written as
(->> #app-state
:contacts
(mapv :first)
first
and it's useful to understand what's going on here.
->> is a macro called thread-last which will re-write the code above to be
(first (mapv :first (:contacts #app-state)))
Thread last is a bit weird at first but it makes the code more readable when lots of things are going on. I suggest that on top of the reagent tutorial mentioned in the other comments, you read this.
#app-state will give you whatever is inside the r/atom and (:first (first (:contacts #app-state))) will return the first element and (println (:first (first (:contacts #app-state)))) will print output to the browser console (so you need to have the developer tools console open to see it).
Note that for println to output to the browser developer tools console you need to have this line in your code:
(enable-console-print!)
I would like to write out an EDN data file from Clojure as tagged literals. Although the clojure.edn API contains read and read-string, there are no writers. I'm familiar with the issue reported here. Based on that, it's my understanding that the pr and pr-str functions are what are meant to be used today.
I wanted to check with the StackOverflow community to see if something like the following would be considered the "correct" way to write out an EDN file:
(spit "friends.edn" (apply str
(interpose "\n\n"
[(pr-str (symbol "#address-book/person") {:name "Janet Wood"})
(pr-str (symbol "#address-book/person") {:name "Jack Tripper"})
(pr-str (symbol "#address-book/person") {:name "Chrissy Snow"})])))
If you are using EDN in production, how do you write out an EDN file? Similar to the above? Are there any issues I need to look out for?
Update
The Clojure Cookbook entry, "Emitting Records as EDN Values" contains a more thorough explanation of this issue and ways to handle it that result in valid EDN tags.
you should not need to generate the tags manually. If you use any of the clojure type definition mechanisms they will be created by the printer. defrecord is particularly convenient for this.
(ns address-book)
(defrecord person [name])
(def people [(person. "Janet Wood")
(person. "Jack Tripper")
(person. "Chrissy Snow")])
address-book> (pr-str people)
"[#address_book.person{:name \"Janet Wood\"}
#address_book.person{:name \"Jack Tripper\"}
#address_book.person{:name \"Chrissy Snow\"}]"
if you want them formatted more nicely you can combine with-out-str and clojure.pprint/pprint. Using Clojure types to create the tags also gives you reading of those tags for free.
address-book> (read-string (pr-str people))
[#address_book.person{:name "Janet Wood"}
#address_book.person{:name "Jack Tripper"}
#address_book.person{:name "Chrissy Snow"}]
address-book> (def read-people (read-string (pr-str people)))
#'address-book/read-people
address-book> (type (first read-people))
address_book.person
The only downside I see is that you lose some control over the way the tags look if you have -'s in your namespace because java classes can't contain these so they get converted to underscores.
I'm trying to generate some Clojure code with type hints, however the type hints seem to disappear whenever I build some code (they also don't function when the code is compiled)
e.g.
`(let [^BufferedImage b (create-buffered-image)]
(.getRGB b 0 0))
=> (clojure.core/let [user/b (user/create-buffered-image)] (.getRGB user/b 0 0))
I'm not precisely sure why the type hint is disappearing, but I assume it is something to do with how metatdata is handled by the reader.
What's the right way to create correct type hints in generated code?
There are two answers to this question. To answer your specific question: in the actual code you just posted, nothing is wrong: it's working just fine. (set! *print-meta* true) and try again, and you'll see the metadata annotation. It just doesn't normally print.
But, in general this is not the right way to do things from a macro, and you will have trouble before long. Remember, you don't want metadata on the forms the macro evaluates, you want metadata on the forms the macro emits. So, a more accurate solution is to use with-meta on the symbols or forms that you want to attach metadata to - or, if they're user-supplied forms, you should usually use vary-meta so that you don't discard the metadata they added explicitly. For example,
(defmacro with-image [name & body]
(let [tagged-name (vary-meta name assoc :tag `BufferedImage)
`(let [~tagged-name (create-buffered-image)
~#body)))
(with-image i (.getRGB i 0 0))
For example, the prxml function prints XML to *out*. I would like to instead capture this output as a String. Here is the typical usage from a REPL:
user> (prxml [:p "Test"])
<p>Test</p>nil
I'd instead like to do:
(def xml (capture-out (prxml [:p "Test"])))
I made up the capture-out function, but I suspect something like it exists, only I'm having trouble finding it in the API or mailing list.
I just discovered the with-out-str from this great blog post detailing XML processing in Clojure.
So the correct implementation of my example is:
(def xml (with-out-str (prxml [:p "Test"])))
More generally, if you look at the source for with-out-str you can see how to dynamically bind *out* to any stream using binding. This works for dynamically setting the value of any existing var.