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darcs get http://www.common-lisp.net/project/submarine/darcs/cl-couch darcs get http://www.common-lisp.net/project/cl-couch/darcs/cl-couch

Overview

["Cl-Couch"] is a Common Lisp suite for interacting with CouchDB databases.

It defines three systems:

  • cl-couchdb-client -- a client server for making requests to a CouchDB database from Common Lisp

  • cl-couchdb-view-server -- a view server for programming CouchDB ["Views"] with Common Lisp

  • cl-couchdb-object-layer -- a simple object layer for making cl-couchdb-client easier to work with

Getting

There are no official releases of ["Cl-Couch"] yet.

Check out the latest version from the [http://darcs.net/ darcs] repo:

darcs get http://www.common-lisp.net/project/cl-couch/darcs/cl-couch

or [http://common-lisp.net/cgi-bin/darcsweb/darcsweb.cgi?r=submarine-cl-couch;a=tree browse] the source code online.

Cl-CouchDB-client

Cl-CouchDB-client allows the user to make requests to the running CouchDB server from lisp. It's main entry point is the macro R.

Starting the server

You start the server with by calling open-server:

COUCHDB-SERVER> (open-server)
*COUCHDB-SERVER*

This sets *COUCHDB-SERVER* to the default http://localhost:5984. This isn't really necessary, but allows us to omit the server argument when we make requests.

COUCH-REQUEST

COUCH-REQUEST takes specifiers for a request to a CouchDB database and returns a Lisp object. HTTP PUT and POST requests with COUCH-REQUEST take Lisp objects as well, thus enabling the programmer to black-box the JSON layer completely.

Examples

Using COUCH-REQUEST to make a GET request to http://localhost:5984/blog/150fedd5d14f0771eb5e44d071a1df5d:

COUCHDB-CLIENT> (couch-request :get (blog "150fedd5d14f0771eb5e44d071a1df5d"))
((:_ID . "150fedd5d14f0771eb5e44d071a1df5d") (:_REV . "253381451")
 (:AUTHOR . "foo") (:BODY . "Zażółć") (:POST . "third") (:TYPE . "comment")
 (:N . 66))

Using COUCH-REQUEST to make a GET request to http://localhost:5984/blog/_all_docs?count=2:

COUCHDB-CLIENT> (couch-request :get (blog _all_docs :count 2))
((:TOTAL-ROWS . 48) (:OFFSET . 0)
 (:ROWS
  ((:ID . "06672346ffc093ce68a07692a5f12db5")
   (:KEY . "06672346ffc093ce68a07692a5f12db5") (:VALUE (:REV . "3441371051")))
  ((:ID . "14328cab564dfec5eac0ff0a44d2083d")
   (:KEY . "14328cab564dfec5eac0ff0a44d2083d") (:VALUE (:REV . "1258191009")))))

COUCH-REQUEST*

COUCH-REQUEST* is the functional equivalent to the macro COUCH-REQUEST.

@

@ is a utility function that enables you to access Lisp data in the JavaScript dot style. For example, (@ doc :friend :id) is equivalent to js doc.friend.id.

When looking into lists, @ does an alist lookup by default. Since it's a generic function, however, it's behavior can be extended for any type of object (eg, those created from CouchDB documents by cl-CouchDB-object-layer).

Cl-CouchDB-View-Server

Cl-CouchDB-View-Server enables you to write views with Common Lisp instead of having to use JavaScript. It supports both standard and mapreduce views.

Writing views with Common Lisp has several advantages:

  • Common Lisp compiles to fast code.
  • Views are compiled (even ad hoc views) since CouchDB usually sends symbols naming functions, rather than their source.
  • You can do all sorts of weird tricks with the running Lisp image, such as maintaining an in-memory database for faster indexed lookup, making requests to the CouchDB server itself, or well... any of the weird things you can do with Lisp...

Starting the Lisp View Server

From the CouchDB side

A Lisp image that with a running view server will be listening to port 5477. So, you need to add something like

common-lisp=/usr/bin/socat -TCP4:localhost:5477

to the [Couch Query Servers] section of your couch.ini (you can substitute socat for any program that will allow a socket open on port 5477 look like a program with standard input and standard output).

From the Lisp Side

The Lisp image just needs to open a client server (we need to be able to speak with couchdb through HTTP) and a view server and it's ready for action.

COUCHDB-SERVER> (open-server)
*COUCHDB-SERVER*

COUCHDB-SERVER> (start-view-server)
#<view-server :host "127.0.0.1" :port 5477>

Creating Design Documents

The DEFDESIGN macro creates a design document and saves it to the database.

This example creates a design document "test" with one view (by-author-type) and saves it to the database "blog":

COUCHDB-SERVER> (defdesign test
                    ((by-author-type :map (doc)
                                     (emit (list (@ doc :author) (@ doc :type)) doc)))
                  (:documentation "A test view.")
                  (:sync blog))
#<design-document :name TEST :revision NIL :views (#<view BY-AUTHOR-TYPE :map "#'CL-COUCHDB-VIEW-SERVER::BY-AUTHOR-TYPE-MAP" :reduce NIL>)>

A :reduce view-function may be called either in the reduce or rereduce phase. In the latter situations it gets as its argument the list of earlier calls to reduce instead the usual list of key-value pairs produced by map. The function may tell whether this is the case by checking the value of the special variable *in-rereduce*.

Querying the View Server

You can query views with the function query-view:

COUCHDB-SERVER> (query-view 'by-author-type :startkey '("foobar") :endkey '("foobar" #()))
(((:ID . "first") (:KEY "foobar" "blogPost")
  (:VALUE (:_ID . "first") (:_REV . "2718626630") (:AUTHOR . "foobar")
   (:BODY . "Zażółć gęślą jaźń") (:TYPE . "blogPost") (:N . 5)))
 ((:ID . "fourth") (:KEY "foobar" "blogPost")
  (:VALUE (:_ID . "fourth") (:_REV . "2695588251") (:AUTHOR . "foobar")
   (:BODY . "Zażółć gęślą jaźń") (:TYPE . "blogPost") (:N . 8)))
 ((:ID . "second") (:KEY "foobar" "blogPost")
  (:VALUE (:_ID . "second") (:_REV . "230136489") (:AUTHOR . "foobar")
   (:BODY . "Zażółć gęślą jaźń") (:TYPE . "blogPost") (:N . 6)))
 ((:ID . "third") (:KEY "foobar" "blogPost")
  (:VALUE (:_ID . "third") (:_REV . "2453743212") (:AUTHOR . "foobar")
   (:BODY . "Zażółć gęślą jaźń") (:TYPE . "blogPost") (:N . 7))))
47
39

You can create ad-hoc views with the function query:

COUCHDB-SERVER> (query 'blog '(lambda (doc) (emit (@ doc :author) (@ doc :body))) :count 2)
(((:ID . "06672346ffc093ce68a07692a5f12db5") (:KEY . "foo")
  (:VALUE . "Zażółć"))
 ((:ID . "146238e235f0cc36661ce82c909044be") (:KEY . "foo")
  (:VALUE . "Zażółć")))
47
0

Cl-CouchDB-Object-Layer

Cl-CouchDB-Object-Layer provides an object abstraction layer over the alists coming in and out of the database. Most importantly, using these objects (called docs) allows you to automatically validate the information coming in and out of the database (preventing other Lispers from polluting your pristine CouchDB database with specious data ;-) )

Defining Doc Classes

To define a doc class, use DEFDOC (which is similar to [http://www.lisp.org/HyperSpec/Body/mac_defclass.html DEFCLASS]).

COUCHDB-OBJECTS> (defdoc blog-post 
                     ((:author :validator #'stringp)
                      (:title :validator #'stringp)
                      (:_id :initform (lambda (doc) (url-encode (@ doc :title))))
                      (:body :validator #'stringp))
                   (:default-db 'blog))
#<STANDARD-METHOD MAKE-DOC ((EQL BLOG-POST)) {BEB6679}>

"Attributes" are like slots, except identified by a keyword. Attributes can have a :VALIDATOR and :INITFORM and :DOCUMENTATION attribute-options (which are liks slot-options for CLOS objects).

  • A :VALIDATOR must be a unary function that take the value of an attribute and returns a non-NULL value if it is valid.

  • An :INITFORM may be either a normal Lisp value or unary function, which is called on the object itself after setting other attributes.

  • a :DOCUMENTATION attribute-option is a doc string.

Making Docs

Use the function MAKE-DOC to make DOCs. MAKE-DOC is something like [http://www.lisp.org/HyperSpec/Body/stagenfun_make-instance.html MAKE-INSTANCE].

COUCHDB-OBJECTS> (make-doc 'blog-post :author "Kuba" :title "O czym dziś napisać" :body "Foo")
#<doc(NIL) :_ID "o_czym_dzis_napisac" :BODY "Foo" :TITLE "O czym dziś napisać" :AUTHOR "Kuba" :TYPE "BLOG-POST">

Getting Data from Docs

You can call @ on docs to get the value of an attribute, exactly as you would call @ on an alist.

COUCHDB-OBJECTS> (let ((doc (make-doc 'blog-post :author "Kuba" :title "O czym dziś napisać" :body "Foo")))
                   (@ doc :title))
"O czym dziś napisać"

Saving Docs

We can call make-and-save to create a document and save it in the database:

COUCHDB-OBJECTS> (make-doc-and-save 'blog-post :author "Kuba" :title "Zażółć gęślą jaźń" :body "foobar") ;we'll get the rev in return
"2591270477"

Note: if an object is invalid, it won't be saved:

COUCHDB-OBJECTS> (make-doc-and-save 'blog-post :author "Kuba" :title "Zażółć gęślą jaźń")
The document #<doc(NIL) :_ID "zazolc_gesla_jazn" :TITLE "Zażółć gęślą jaźń" :AUTHOR "Kuba" :TYPE "BLOG-POST"> is invalid. Reason: attribute
                      :BODY with value NIL didn't validate using #<FUNCTION STRINGP>
   [Condition of type VALIDATOR-FAILED]
...

License

BSD sans advertising clause.

Author

Ryszard Szopa <ryszard.szopa@gmail.com>, with one component (logv) being authored by Nick Allen <nallen05@gmail.com>.