Clutch

Clutch is a Clojure library for Apache CouchDB.

"Installation"

To include Clutch in your project, simply add the following to your project.clj dependencies:

[com.ashafa/clutch "0.4.0"]

Or, if you're using Maven, add this dependency to your pom.xml:

<dependency>
    <groupId>com.ashafa</groupId>
    <artifactId>clutch</artifactId>
    <version>0.4.0</version>
</dependency>

Clutch is compatible with Clojure 1.2.0+, and requires Java 1.5+.

Status

Although it's in an early stage of development (Clutch API subject to change), Clutch supports most of the Apache CouchDB API:

• Essentially all of the core document API
• Bulk document APIs
• Most of the Database API, including _changes and a way to easily monitor/react to _changes events using Clojure's familiar watch mechanism
• Views, including access, update, and a Clojure view server implementation

Read the documentation to learn the basics of Clutch. You can also look at the source or introspect the docs once you've loaded Clutch in your REPL.

Clutch does not currently provide any direct support for the various couchapp-related APIs, including update handlers and validation, shows and lists, and so on.

That said, it is very easy to call whatever CouchDB API feature that Clutch doesn't support using the lower-level com.ashafa.clutch.http-client/couchdb-request function.

Usage

First, a basic REPL interaction:

=> (get-database "clutch_example")  ;; creates database if it's not available yet
#cemerick.url.URL{:protocol "http", :username nil, :password nil, :host "localhost", :port -1,
:path "clutch_example", :query nil, :disk_format_version 5, :db_name "clutch_example", :doc_del_count 0,
:committed_update_seq 0, :disk_size 79, :update_seq 0, :purge_seq 0, :compact_running false,
:instance_start_time "1323701753566374", :doc_count 0}

=> (bulk-update "clutch_example" [{:test-grade 10 :_id "foo"}
                                  {:test-grade 20}
                                  {:test-grade 30}])
[{:id "foo", :rev "1-8a15da0db077cd05b45ec93b3a207d09"}
 {:id "0896fbf57128d7f1a1b238a52b0ec372", :rev "1-796ebf042b42fa3585332c3aa4a6f706"}
 {:id "0896fbf57128d7f1a1b238a52b0ecda8", :rev "1-01f063c5aeb1b63992c90c72c7a515ed"}]
=> (get-document "clutch_example" "foo")
{:_id "foo", :_rev "1-8a15da0db077cd05b45ec93b3a207d09", :test-grade 10}

All Clutch functions accept a first argument indicating the database endpoint for that operation. This argument can be:

• a cemerick.url.URL record instance (from the url library)
• a string URL
• the name of the database to target on http://localhost:5984

You can assoc in whatever you like to a URL record, which is handy for keeping database URLs and credentials separate:

=> (def db (assoc (cemerick.url/url "https://XXX.cloudant.com/" "databasename")
                    :username "username"
                    :password "password"))
#'test-clutch/db
=> (put-document db {:a 5 :b [0 6]})
{:_id "17e55bcc31e33dd30c3313cc2e6e5bb4", :_rev "1-a3517724e42612f9fbd350091a96593c", :a 5, :b [0 6]}

Of course, you can use a string containing inline credentials as well:

=> (put-document "https://username:[email protected]/databasename/" {:a 5 :b 6})
{:_id "36b807aacf227f921aa256b06ab094e5", :_rev "1-d4d04a5b59bcd73893a84de2d9595c4c", :a 5, :b 6}

Finally, you can optionally provide configuration using dynamic scope via with-db:

=> (with-db "clutch_example"
     (put-document {:_id "a" :a 5})
     (put-document {:_id "b" :b 6})
     (-> (get-document "a")
       (merge (get-document "b"))
       (dissoc-meta)))
{:b 6, :a 5}

Experimental: a Clojure-idiomatic CouchDB type

Clutch provides a pretty comprehensive API, but 95% of database interactions require using something other than the typical Clojure vocabulary of assoc, conj, dissoc, get, seq, reduce, etc, even though those semantics are entirely appropriate (modulo the whole stateful database thing).

This is (the start of) an attempt to create a type to provide most of the functionality of Clutch with a more pleasant, concise API (it uses the Clutch API under the covers, and rare operations will generally remain accessible only at that lower level).

Would like to eventually add:

• support for views (aside from _all_docs via seq)
• support for _changes (via a seque?), maybe a more natural place than the (free-for-all) pool of watches in Clutch's current API
• support for bulk update, maybe via IReduce?
• Other CouchDB types: ** to provide specialized query interfaces e.g. cloudant indexes ** to return custom map and vector types to support e.g.

(assoc-in! db ["ID" :key :key array-index] x)
(update-in! db ["ID" :key :key array-index] assoc :key y)

Feedback wanted on the mailing list: http://groups.google.com/group/clojure-clutch

This part of the API is subject to change at any time, so no detailed examples. For now, just a REPL interaction will do:

=> (use 'com.ashafa.clutch)     ;; My apologies for the bare `use`!
nil
=> (def db (couch "test"))
#'user/db
=> (create! db)
#<CouchDB user.CouchDB@3f460a4a>
=> (:result (meta *1))
#com.ashafa.clutch.utils.URL{:protocol "http", :username nil, :password nil,
:host "localhost", :port -1, :path "test", :query nil, :disk_format_version 5,
:db_name "test", :doc_del_count 0, :committed_update_seq 0, :disk_size 79,
:update_seq 0, :purge_seq 0, :compact_running false, :instance_start_time
"1324037686108297", :doc_count 0}
=> (reduce conj! db (for [x (range 5000)]
                      {:_id (str x) :a [1 2 x]}))
#<CouchDB user.CouchDB@71d1be4e>
=> (count db)
5000
=> (get-in db ["68" :a 2])
68
=> (def copy (into {} db))
#'user/copy
=> (get-in copy ["68" :a 2])
68
=> (first db)
["0" {:_id "0", :_rev "1-79fe783154bff972172bc30732783a68", :a [1 2 0]}]
=> (dissoc! db "68")
#<CouchDB user.CouchDB@48f50903>
=> (get db "68")
nil
=> (assoc! db :foo {:a 6 :b 7})
#<CouchDB user.CouchDB@79d7999e>
=> (:result (meta *1))
{:_rev "1-ac3fe57a7604cfd6dcca06b25204b590", :_id ":foo", :a 6, :b 7}

Using ClojureScript to write CouchDB views

You can write your views/filters/validators in Clojure(Script) — avoiding the use of any special view server, special configuration, or JavaScript!

Depending on the requirements of your view functions (e.g. if your views have no specific dependencies on Clojure or JVM libraries), then writing your views in ClojureScript can have a number of benefits:

1. No need to configure CouchDB instances to use the Clojure/Clutch view server.
2. Therefore, flexibility to use hosted CouchDB services like Cloudant, Iris Couch, et al.
3. Did we say 'no JavaScript'? Yup, no JavaScript. :-)

"Installation"

Clutch provides everything necessary to use ClojureScript to define CouchDB views, but it does not declare a specific ClojureScript dependency. This allows you to bring your own revision of ClojureScript into your project, and manage it without worrying about dependency management conflicts and such.

You can always look at Clutch's project.clj to see which version of ClojureScript it is currently using to test its view support ( [org.clojure/clojurescript "0.0-1011"] as of this writing).

Note that while Clutch itself only requires Clojure >= 1.2.0 ClojureScript requires Clojure >= 1.4.0.

The above requirement applies only if you are saving ClojureScript views. A Clutch client using Clojure 1.2.0 can access views written in ClojureScript (i.e. via get-view) without any dependence on ClojureScript at all.

If you attempt to save a ClojureScript view but ClojureScript is not available (or you are using Clojure 1.2.x), an error will result.

Usage

Use Clutch's save-view per usual, but instead of providing a string of JavaScript (and specifying the language to be :javascript), provide a snippet of ClojureScript (specifying the language to be :cljs):

(with-db "your_database"
  (save-view "design_document_name"
    (view-server-fns :cljs
      {:your-view-name {:map (fn [doc]
                               (js/emit (aget doc "_id") nil))}})))

(Note that view-server-fns is a macro, so you do not need to quote your ClojureScript forms.)

That's an example of a silly view, but should demonstrate the general pattern. Note the js/emit function; after ClojureScript compilation, this results in a call to the emit function defined by the standard CouchDB Javascript view server for emitting an entry into the view result. Follow the same conventions for reduce functions, filter functions, validator functions, etc.

Your views can utilize larger codebases; just include your "top-level" ClojureScript forms in a vector:

(with-db "your_database"
  (save-view "design_document_name"
    (view-server-fns {:language :cljs
                      :main 'couchview/main}
      {:your-view-name {:map [(ns couchview)
                              (defn concat
                                [id rev]
                                (str id rev))
                              (defn ^:export main
                                [doc]
                                (js/emit (concat (aget doc "_id") (aget doc "_rev")) nil))]}})))

The ns form here can require other ClojureScript files on your classpath, refer to macros, etc. When using this longer form, remember to do three things:

1. You must provide a map of options to view-server-fns; :cljs becomes the :language value here.
2. Specify the "entry point" for the view function via the :main slot, 'couchview/main here. This must correspond to an exported, defined function loaded by some ClojureScript, either in your vector literal of in-line ClojureScript, or in some ClojureScript loaded via a :require.
3. Ensure that your "entry point" function is exported; here, main is our entry point, exported via the ^:export metadata.

These last two points are required because of the default ClojureScript compilation option of :advanced optimizations.

Compilation options

The view-server-fns macro provided by Clutch takes as its first argument some options to pass along to the view transformer specified in that options map's :language slot. The :cljs transformer passes this options map along to the ClojureScript/Google Closure compiler, with defaults of:

{:optimizations :advanced
 :pretty-print false}

So you can e.g. disable :advanced optimizations and turn on pretty-printing by passing this options map to view-server-fns:

{:optimizations :simple
 :pretty-print true
 :language :cljs}

Internals

If you really want to see what Javascript ClojureScript is generating for your view function(s), call com.ashafa.clutch.cljs-views/view with an options map as described above (nil to accept the defaults) and either an anonymous function body or vector of ClojureScript top-level forms.

Caveats

• ClojureScript / Google Closure produces a very large code footprint, even for the simplest of view functions. This is apparently an item of active development in ClojureScript.
  • In any case, the code size of a view function string should have little to no impact on runtime performance of that view. The only penalty to be paid should be in view server initialization, which should be relatively infrequent. Further, the vast majority of view runtime is dominated by IO and actual document processing, not the loading of a handful of JavaScript functions.
• The version of Spidermonkey that is used by CouchDB (and Cloudant at the moment) does not treat regular expression literals properly — they work fine as arguments, e.g. string.match(/foo/), but e.g. /foo/.exec("string") fails. Using the RegExp() function with a string argument does work. This is reportedly fixed in CouchDB 1.2.0, though I haven't verified that.
• If you are familiar with writing CouchDB views in JavaScript, you must keep a close eye on your ClojureScript/JavaScript interop. e.g. (js/emit [1 2] true) will do nothing, because [1 2] is a ClojureScript vector, not a JavaScript array. Similarly, the values passed to view functions are JavaScript objects and arrays, not ClojureScript maps and vectors. A later release of Clutch will likely include a set of ClojureScript helper functions and macros that will make the necessary conversions automatic.

Configuring your CouchDB installation to use the Clutch view server

This section is only germane if you are going to use Clutch's Clojure (i.e. JVM Clojure) view server. If the views you need to write can be expressed using ClojureScript — i.e. they have no JVM or Clojure library dependencies — using Clutch's ClojureScript support to write views is generally recommended.

CouchDB needs to know how to exec Clutch's view server. Getting this command string together can be tricky, especially given potential classpath complexity. You can either (a) produce an uberjar of your project, in which case the exec string will be something like:

java -cp <path to your uberjar> clojure.main -m com.ashafa.clutch.view-server

or, (b) you can use the com.ashafa.clutch.utils/view-server-exec-string function to dump a likely-to-work exec string. For example:

user=> (use '[com.ashafa.clutch.view-server :only (view-server-exec-string)])
nil
user=> (println (view-server-exec-string))
java -cp "clutch/src:clutch/test:clutch/classes:clutch/resources:clutch/lib/clojure-1.3.0-beta1.jar:clutch/lib/clojure-contrib-1.2.0.jar:clutch/lib/data.json-0.1.1.jar:clutch/lib/tools.logging-0.1.2.jar" clojure.main -m com.ashafa.clutch.view-server

This function assumes that java is on CouchDB's PATH, and it's entirely possible that the classpath might not be quite right (esp. on Windows — the above only tested on OS X and Linux so far). In any case, you can test whether the view server exec string is working properly by trying it yourself and attempting to get it to echo back a log message:

[catapult:~/dev/clutch] chas% java -cp "clutch/src:clutch/test:clutch/classes:clutch/resources:clutch/lib/clojure-1.3.0-beta1.jar:clutch/lib/clojure-contrib-1.2.0.jar:clutch/lib/data.json-0.1.1.jar:clutch/lib/tools.logging-0.1.2.jar" clojure.main -m com.ashafa.clutch.view-server
["log" "echo, please"]
["log",["echo, please"]]

Enter the first JSON array, and hit return; the view server should immediately reply with the second JSON array. Anything else, and your exec string is flawed, or something else is wrong.

Once you have a working exec string, you can use Clojure for views and filters by adding a view server configuration to CouchDB. This can be as easy as passing the exec string to the com.ashafa.clutch/configure-view-server function:

(configure-view-server (view-server-exec-string))

Alternatively, use Futon to add the clojure query server language to your CouchDB instance's config.

In the end, both of these methods add the exec string you provide it to the local.ini file of your CouchDB installation, which you can modify directly if you like (this is likely what you'll need to do for non-local/production CouchDB instances):

  [query_servers]
  clojure = java -cp …rest of your exec string…

View server configuration & view API usage

=> (configure-view-server "clutch_example" (com.ashafa.clutch.view-server/view-server-exec-string))
""
=> (save-view "clutch_example" "demo_views" (view-server-fns :clojure
                                              {:sum {:map (fn [doc] [[nil (:test-grade doc)]])
                                                     :reduce (fn [keys values _] (apply + values))}}))
{:_rev "1-ddc80a2c95e06b62dd2923663dc855aa", :views {:sum {:map "(fn [doc] [[nil (:test-grade doc)]])", :reduce "(fn [keys values _] (apply + values))"}}, :language :clojure, :_id "_design/demo_views"}
=> (-> (get-view "clutch_example" "demo_views" :sum) first :value)
60
=> (get-view "clutch_example" "demo_views" :sum {:reduce false})
({:id "0896fbf57128d7f1a1b238a52b0ec372", :key nil, :value 20}
 {:id "0896fbf57128d7f1a1b238a52b0ecda8", :key nil, :value 30}
 {:id "foo", :key nil, :value 10})
=> (map :value (get-view "clutch_example" "demo_views" :sum {:reduce false}))
(20 30 10)

Note that all view access functions (i.e. get-view, all-documents, etc) return a lazy seq of their results (corresponding to the :rows slot in the data that couchdb returns in its view data). Other values (e.g. total_rows, offset, etc) are added to the returned lazy seq as metadata.

=> (meta (all-documents "databasename"))
{:total_rows 20000, :offset 0}

_changes support

Clutch provides comprehensive support for CouchDB's _changes feature. There is a com.ashafa.clutch/changes function that provides direct access to it, but most uses of _changes will benefit from using the change-agent feature. This configures a Clojure agent to receive updates from the _changes feed; its state will be updated to be the latest event (change notification), and so it is easy to hook up however many functions as necessary to the agent as watches (a.k.a. callbacks).

Here's a REPL interaction demonstrating this functionality:

=> (require '[com.ashafa.clutch :as couch])
nil
=> (couch/create-database "demo")
#cemerick.url.URL{:protocol "http", :username nil, :password nil,
                  :host "localhost", :port 5984, :path "/demo",
                  :query nil, :anchor nil}
=> (def a (couch/change-agent "demo"))
#'user/a

   ;; `start-changes` hooks the agent up to the database's `_changes` feed
=> (couch/start-changes a)
#<Agent@693a1324: nil>
=> (couch/put-document "demo" {:name "Chas"})
{:_id "259239233e2c2d06f3e311ce5f5271c1", :_rev "1-24ccfd9600c215e32ceefdd06b25f62d", :name "Chas"}

   ;; each change becomes a new state within the agent:
=> @a
{:seq 1, :id "259239233e2c2d06f3e311ce5f5271c1", :changes [{:rev "1-24ccfd9600c215e32ceefdd06b25f62d"}]}

   ;; use Clojure's watch facility to have functions called on each change
=> (add-watch a :echo (fn [key agent previous-change change]
                        (println "change received:" change)))
#<Agent@693a1324: {:seq 1, :id "259239233e2c2d06f3e311ce5f5271c1", :changes [{:rev "1-24ccfd9600c215e32ceefdd06b25f62d"}]}>
=> (couch/put-document "demo" {:name "Roger"})
{:_id "259239233e2c2d06f3e311ce5f527a9d", :_rev "1-0c3db91854f26486d1c3922f1a651d86", :name "Roger"}
change received: {:seq 2, :id 259239233e2c2d06f3e311ce5f527a9d, :changes [{:rev 1-0c3db91854f26486d1c3922f1a651d86}]}
=> (couch/bulk-update "demo" [{:x 1} {:y 2} {:z 3 :_id "some-id"}])
[{:id "259239233e2c2d06f3e311ce5f527cd4", :rev "1-0785e9eb543380151003dc452c3a001a"} {:id "259239233e2c2d06f3e311ce5f527fa6", :rev "1-ef91d626f27dc5d224fd534e7b47da82"} {:id "some-id", :rev "1-178dbe6c7346ffc3af8811327d1336ff"}]
change received: {:seq 3, :id 259239233e2c2d06f3e311ce5f527cd4, :changes [{:rev 1-0785e9eb543380151003dc452c3a001a}]}
change received: {:seq 4, :id 259239233e2c2d06f3e311ce5f527fa6, :changes [{:rev 1-ef91d626f27dc5d224fd534e7b47da82}]}
change received: {:seq 5, :id some-id, :changes [{:rev 1-178dbe6c7346ffc3af8811327d1336ff}]}
=> (couch/delete-document "demo" (couch/get-document "demo" "some-id"))
{:ok true, :id "some-id", :rev "2-7a128852666329025f1fba1114628251"}
change received: {:seq 6, :id some-id,
                  :changes [{:rev 2-7a128852666329025f1fba1114628251}], :deleted true}

   ;; if you want to stop the flow of changes through the agent, use
   ;; `stop-changes`
=> (couch/stop-changes a)
#<Agent@693a1324: {:seq 6, :id "some-id", :changes [{:rev "2-7a128852666329025f1fba1114628251"}], :deleted true}>

changes and change-agent pass along all of the parameters accepted by _changes, so you can get changes since a given point in time, filter changes based on a view server function, get the full content of changed documents included in the feed, etc. See the official CouchDB API documentation for _changes for details.

(Partial) Changelog

0.4.0

• API change: watch-changes, stop-changes, and changes-error have been removed. See the usage section on changes above. The _changes API support now consists of:
  • changes to obtain a lazy seq of updates from _changes directly
  • change-agent, start-changes, and stop-changes for creating and then controlling the activity of a Clojure agent whose state reflects the latest row from a continuous or longpoll view of _changes.
• API change: com.ashafa.clutch.http-client/*response-code* has been replaced by *response*. Rather than just being optionally bound to the response code provided by CouchDB, this var is set!ed to its complete clj-http response.
• Added document-exists? function; same as (boolean (get-document db "key")), but uses a HEAD request instead of a GET (handy for checking for the existence of very large documents).
• Write CouchDB views in ClojureScript! All of the functionality of clutch-clojurescript has been merged into Clutch proper.
• cheshire is now being used for all JSON operations.
• clj-http is now being used for all HTTP operations.

0.3.1

• Added the CouchDB "type", providing a higher-level and more Clojuresque abstraction for most CouchDB operations.
• byte arrays may now be used with put-attachment et al.
• Clutch may now be used with Java 1.5 (in addition to 1.6+)

0.3.0

Many breaking changes to refine/simplify the API, clean up the implementation, and add additional features:

Core API:

• Renamed create-document => put-document; put-document now supports both creation and update of a document depending upon whether :_id and :_rev slots are present in the document you are saving.
• Renamed update-attachment => put-attachment; filename and mime-type arguments now kwargs, InputStream can now be provided as attachment data
• update-document semantics have been simplified for the case where an "update function" and arguments are supplied to work well with core Clojure functions like update-in and assoc (fixes issue #8) — e.g. can be used like swap! et al.
• Optional :id and :attachment arguments to put-document (was create-document) are now specified via keyword arguments
• Removed "update map" argument from bulk-update fn (replace with e.g. (bulk-update db (map #(merge % update-map) documents))
• Renamed get-all-documents-meta => all-documents
• com.ashafa.clutch.http-client/*response-code* is no longer assumed to be an atom. Rather, it is set!-ed directly when it is thread-bound. (Fixes issue #29)

View-related API:

• All views (get-view, all-documents, etc) now return lazy seqs corresponding to the :rows slot in the view data returned by couch. Other values (e.g. total_rows, offset, etc) are added to the returned lazy seq as metadata.
• elimination of inconsistency between APIs between save-view and save-filter. The names of individual views and filters are now part of the map provided to these functions, instead of sometimes being provided separately.
• :language has been eliminated as part of the dynamically-bound configuration map
• with-clj-view-server has been replaced by the more generic view-server-fns macro, which takes a :language keyword or map of options that includes a :language slot (e.g. :clojure, :javascript, etc), and a map of view/filter/validator names => functions.
• A view-transformer multimethod is now available, which opens up clutch to dynamically support additional view server languages.
• Moved view-server-exec-string to com.ashafa.clutch.view-server namespace

Contributors

Appreciations go out to:

• Chas Emerick
• Tunde Ashafa
• Pierre Larochelle
• Matt Wilson
• Patrick Sullivan
• Toni Batchelli
• Hugo Duncan
• Ryan Senior

License

BSD. See the LICENSE file at the root of this repository.