I have a strange problem here. I am calling dates from a database and I am attempting to show the PostgreSQL dates, formatted as "2013-01-01", to display on my site as "January 1, 2013"
I have the following code:
(ns mr.layouts
(:require
[clj-time.format :as ctf]))
(def to-mdy (ctf/formatter "MMMM d, yyyy"))
(defn coerce-mdy [sd]
(ctf/unparse to-mdy (ctf/parse sd)))
The call to the database looks like:
(layouts/coerce-mdy startdate)
The above code does what I want if I test it from the REPL:
mr.handler=> (use 'mr.layouts)
nil
mr.handler=> (require '[clj-time.format :as ctf])
nil
mr.handler=> (coerce-mdy "2012-01-01")
"January 1, 2012"
mr.handler=> (coerce-mdy "2014-10-04")
"October 4, 2014"
mr.handler=>
But what I am getting on the webpage is "September 1, 2013" (today as of this writing) and no other dates. I don't have "2013-09-01" in the database.
I've returned the raw date-value from the data base from (coerse-mdy) and it returns the correct date, so the closest I've been able to isolate this issue is in either (to-mdy) or (coerce-mdy).
So far, I've tried moving the function to the local namespace and using localized let values.
When using clj-time with a database, I've found that I need to use the functions to-sql-date and from-sql-date in the coerce namespace (source here: https://github.com/clj-time/clj-time/blob/master/src/clj_time/coerce.clj)
This is because, as #noisesmith mentioned in his comment, most clojure sql libraries will give a date object (specifically, a java.sql.Date) for a date field in the db. This needs to be treated slightly differently from a string in order to get something that plays nice with clj-time.
Assuming your date is indeed a java.sql.Date, the following should do the trick...
(ns mr.layouts
(:require [clj-time.format :as ctf]
[clj-time.coerce :as coerce]))
(def to-mdy (ctf/formatter "MMMM d, yyyy"))
(defn coerce-mdy [sd]
(ctf/unparse to-mdy (coerce/from-sql-date sd)))
Related
I'm trying to figure out how to do custom coercion with compojure-api and spec. By reading the docs and code I have been able to do coercion on the input (the body) but am unable to do coercion on the response body.
Specifically, I have a custom type, a timestamp, that is represented as a long within my app but for the web API I want to consume and return ISO timestamps (no, I don't want to use Joda internally).
The following is what I have that works for input coercion but I have been unable to properly coerce the response.
(ns foo
(:require [clj-time.core :as t]
[clj-time.coerce :as t.c]
[spec-tools.conform :as conform]
[spec-tools.core :as st]))
(def timestamp (st/create-spec
{:spec pos-int?
:form `pos-int?
:json-schema/default "2017-10-12T05:04:57.585Z"
:type :timestamp}))
(defn json-timestamp->long [_ val]
(t.c/to-long val))
(def custom-json-conforming
(st/type-conforming
(merge
conform/json-type-conforming
{:timestamp json-timestamp->long}
conform/strip-extra-keys-type-conforming)))
(def custom-coercion
(-> compojure.api.coercion.spec/default-options
(assoc-in [:body :formats "application/json"] custom-json-
conforming)
compojure.api.coercion.spec/create-coercion))
;; how do I use this for the response coercion?
(defn timestamp->json-string [_ val]
(t.c/to-string val))
;; I've tried the following but it doesn't work:
#_(def custom-coercion
(-> compojure.api.coercion.spec/default-options
(assoc-in [:body :formats "application/json"] custom-json-
conforming)
(assoc-in [:response :formats "application/json"]
(st/type-conforming
{:timestamp timestamp->json-string}))
compojure.api.coercion.spec/create-coercion))
Problem is that Spec Conforming is a one-way transformation pipeline:
s/conform (and because of that st/conform) does both transform and validate for the result. Your response coercion first converts the integer into date string and the validates it against the original spec predicate, which is pos-int? and it fails on that.
To support two-way transformations, you need to define the end result as either of the possible formats: e.g. change your predicate to something like #(or (pos-int? %) (string? %)) and it should work.
Or you can have two different Spec Records, one for input (timestamp-long with pos-int? predicate) and another for outputs (timestamp-string with string? predicate). But one needs to remember to use correct ones for request & responses.
CLJ-2251 could possible help if there was and extra :transform mode (not written in the issue yet), which would do conforming without validating the end results.
Normally, return transformations are done by the format encoder, but they usually dispatch on value types. For example Cheshire just sees an Long and has no clue that it should be written as date string.
Maybe people on the #clojure-spec slack could help. Would also like to know how to build this kind of two-way transformation with spec.
Although the below example seems a bit strange, it's because I'm trying to reduce a fairly large problem I've got at present to a minimal example. I'm struggling to work out how to call into multimethods when they're sitting behind a couple of abstraction layers and the defmulti and corresponding defmethods are defined in multiple namespaces. I really feel like I'm missing something obvious here...
Suppose I've got the following scenario:
I purchase stuff from a variety of suppliers, via their own proprietary interfaces
I want to implement a common interface to talk to each of those suppliers
I want to be able to purchase different items from different suppliers
Using Clojure, the recommended ways of implementing a common interface would be via protocols or multimethods. In this case, as I'm switching based on the value of the supplier, I think the best way to handle the situation I'm describing below is via multimethods (but I could be wrong).
My multimethod definitions would look something like this, which defines a common interface I want to use to talk to every supplier's APIs:
(ns myapp.suppliers.interface)
(defmulti purchase-item :supplier)
(defmulti get-item-price :supplier)
For each supplier, I probably want something like:
(ns myapp.suppliers.supplier1
(:require [myapp.suppliers.interface :as supplier-api]))
(defmethod purchase-item :supplier1 [item quantity] ...)
(defmethod get-item-price :supplier1 [item] ...)
and
(ns myapp.suppliers.supplier2
(:require [myapp.suppliers.interface :as supplier-api]))
(defmethod purchase-item :supplier2 [item quantity] ...)
(defmethod get-item-price :supplier2 [item] ...)
So far, no problem
Now to my code which calls these abstracted methods, which I assume looks something like:
(ns myapp.suppliers.api
(:require [myapp.suppliers.supplier1 :as supplier1]
[myapp.suppliers.supplier2 :as supplier2])
(defn buy-something
[supplier item quantity]
(purchase-item [supplier item quantity])
(defn price-something
[supplier item]
(get-item-price [supplier item])
This is starting to look a bit ... ugly. Every time I implement a new supplier's API, I'll need to change myapp.suppliers.api to :require that new supplier's methods and recompile.
Now I'm working at the next level up, and I want to buy a widget from supplier2.
(ns myapp.core
(:require [myapp.suppliers.api :as supplier])
(def buy-widget-from-supplier2
(buy-something :supplier2 widget 1)
This can't work, because :supplier2 hasn't been defined anywhere in this namespace.
Is there a more elegant way to write this code? In particular, in myapp.core, how can I buy-something from :supplier2?
Initial notes
It's hard to tell if you mixed up some things in the process of simplifying the example, or if they weren't quite right out of the gate. For an example of what I'm referring to, consider purchase-item, though the issues are similar for get-item-price:
The defmulti call is a single-argument function
The defmethod calls each take two arguments
The call in buy-something passes a vector to purchase-item, but looking up the :supplier keyword in a vector will always return nil
Your concerns
Every time I implement a new supplier's API, I'll need to change myapp.suppliers.api to :require that new supplier's methods and recompile.
If you require the myapp.suppliers.interface namespace myapp.suppliers.api, the problem can be avoided
This can't work, because :supplier2 hasn't been defined anywhere in this namespace.
Simply put, this will work. :)
Is there a more elegant way to write this code? In particular, in myapp.core, how can I buy-something from :supplier2?
Certainly, but this solution is going to make some assumption based on the ambiguities in the Initial notes.
Without straying too far from your original design, here's a fully-working example of how I interpret what you were trying to achieve:
myapp.suppliers.interface
(ns myapp.suppliers.interface)
(defmulti purchase-item (fn [supplier item quantity] supplier))
myapp.suppliers.supplier1
(ns myapp.suppliers.supplier1
(:require [myapp.suppliers.interface :as supplier-api]))
(defmethod supplier-api/purchase-item :supplier1 [supplier item quantity]
(format "Purchasing %dx %s from %s" quantity (str item) (str supplier)))
myapp.suppliers.supplier2
(ns myapp.suppliers.supplier2
(:require [myapp.suppliers.interface :as supplier-api]))
(defmethod supplier-api/purchase-item :supplier2 [supplier item quantity]
(format "Purchasing %dx %s from %s" quantity (str item) (str supplier)))
myapp.suppliers.api
(ns myapp.suppliers.api
(:require [myapp.suppliers.interface :as interface]))
(defn buy-something [supplier item quantity]
(interface/purchase-item supplier item quantity))
myapp.core
(ns myapp.core
(:require [myapp.suppliers.api :as supplier]))
(def widget {:id 1234 :name "Monchkin"})
(supplier/buy-something :supplier1 widget 15)
;;=> "Purchasing 15x {:id 1234, :name \"Monchkin\"} from :supplier1"
(supplier/buy-something :supplier2 widget 3)
;;=> "Purchasing 3x {:id 1234, :name \"Monchkin\"} from :supplier2"
As you can see, the supplier/buy-something calls propagate to the appropriate multimethod implementations. Hopefully this helps you get where you were trying to go.
I have an instant time in clojure as "2016-08-03T18:45:00.000-00:00". I want to convert it to only date ("2016-08-03"). How do I do this.
My actual date is in the format "2016-08-03T18:45:00Z". I converted it to instant using (c/to-date (f/parse "2016-08-03T18:45:00Z")).How to get only date?
Thank you
clj-time is now deprecated, new projects should use java-time:
(:require [java-time :as jt]))
(defn format-date
"Format a Java instant"
[date]
(let [formatter (jt/format "dd-MM-yyyy HH:mm")
instant-with-zone (.atZone date (jt/zone-id))]
(jt/format formatter instant-with-zone)))
Note that (jt/zone-id) returns the current server zone, so you must use (jt/zone-id "America/Mexico_City") if you want a static zoned date.
If you want to get just the date part of the date and time string:
(require '[clojure.string :as str])
(def date-str "2016-08-03T18:45:00.000-00:00")
(first (str/split date-str #"T"))
;; => "2016-08-03"
I just started to play with wit/duckling. It is written in Clojure and I have no previous experience in Clojure. I need to parse a string like 2016-08-14T19:45:48.000+05:30 to a format like 1945hrs, Sunday, August 14th 2016. I searched on Internet and came across to lib clj-time. After struggling with it for a long time I came across this thread and thought that rfc822 is my cup of tea. So I used formatter rfc822 but it is giving me exception:
java.lang.IllegalArgumentException: Invalid format: "2016-08-16T00:00:00.000+05:30"
Here is my code:
(ns firstproj.core
(:gen-class)
(:require [duckling.core :as p])
(:require [clj-time.format :as f]))
(defn -main
"I don't do a whole lot."
[x]
(p/load! { :languages ["en"]})
(def var_ (p/parse :en$core x [:time]))
(def date_string "2016-08-14T19:45:48.000+05:30")
(f/parse (f/formatters :rfc822) date_string))
So can anybody tell me what I am doing wrong here. Or any other way in Clojure to get my desired date-time format. As I am completely naive in Clojure, I request you to answer in detail, it will help me to understand this in a better way. Thank You.
The clj-time library is a wrapper for Joda-Time. If you're using Java 8, you should prefer the built-in java.time library over Joda-Time, for reasons explained here. In Clojure, you can use the Clojure.Java-Time library, which wraps java.time. First, add it to your dependencies:
[clojure.java-time "0.2.1"]
Then you can use the offset-date-time and format functions in the java-time namespace:
(require '[java-time :as time])
(->> (time/offset-date-time "2016-08-14T19:45:48.000+05:30")
(time/format "HHmm'hrs', EEEE, MMMM d y"))
;;=> "1945hrs, Sunday, August 14 2016"
As #Piotrek pointed out in his answer, Joda-Time doesn't seem to support the "th" in your original question. Judging from the DateTimeFormatter docs, neither does java.time.
Without actually checking which predefined formatter matches your date format you might just call:
(f/parse "2016-08-14T19:45:48.000+05:30")
;; => #object[org.joda.time.DateTime 0x1bd11b14 "2016-08-14T14:15:48.000Z"]
It will try all predefined formatters and return parsed value from the first one that succeeds.
Then to print in your custom format:
(require '[clj-time.core :as t])
(def my-time-zone (t/time-zone-for-offset 5 30))
(def my-formatter
(f/formatter
"HHmm'hrs', EEEE, MMMM dd yyyy"
my-time-zone))
(f/unparse my-formatter some-date)
;; => "1945hrs, Sunday, August 14 2016"
Unfortunately to my knowledge JodaTime doesn't handle things like adding st, nd, rd, th to days.
I am using the following code:
(require '[clj-time.core :as time]
'[clj-time.coerce :as tc]
'[clj-time.format :as f])
(f/unparse (f/formatter "yyyyMMdd") time/now)
But it throws the following error.
caused by: java.lang.ClassCastException: clj_time.core$now cannot be cast to org.joda.time.ReadableInstant
unparse function takes 2 arguments. First is the format,which should be an instance of org.joda.time.format.DateTimeFormatter, which you create correctly by calling
(f/formatter "yyyyMMdd")
the second argument is date time, which should be an instance of org.joda.time.DateTime and here you are doing small mistake. Instead of passing DateTime you are passing clojure function time/now, what you should do is to call the function like this
(f/unparse (f/formatter "yyyyMMdd") (time/now))