[CouchDB] CouchDB on NodeJS, cradle

CouchDB 사용할 수 있도록 기본 정보가 제공되어 있음.

출처 : https://github.com/cloudhead/cradle

기본 튜토리얼 내용

  var cradle = require('cradle');
  var db = new(cradle.Connection)().database('starwars');

  db.get('vader', function (err, doc) {
      doc.name; // 'Darth Vader'
      assert.equal(doc.force, 'dark');
  });

  db.save('skywalker', {
      force: 'light',
      name: 'Luke Skywalker'
  }, function (err, res) {
      if (err) {
          // Handle error
      } else {
          // Handle success
      }
  });

installation

  $ npm install cradle

API

Cradle's API builds right on top of Node's asynch API. Every asynch method takes a callback as its last argument. The return value is an event.EventEmitter, so listeners can also be optionally added.

Opening a connection

  new(cradle.Connection)('http://living-room.couch', 5984, {
      cache: true,
      raw: false
  });

Defaults to 127.0.0.1:5984

Note that you can also use cradle.setup to set a global configuration:

  cradle.setup({
    host: 'living-room.couch',
    cache: true,
    raw: false
  });

  var c = new(cradle.Connection),
     cc = new(cradle.Connection)('173.45.66.92');

creating a database

  var db = c.database('starwars');
  db.create();

checking for database existence

You can check if a database exists with the exists() method.

  db.exists(function (err, exists) {
    if (err) {
      console.log('error', err);
    } else if (exists) {
      console.log('the force is with you.');
    } else {
      console.log('database does not exists.');
      db.create();
      /* populate design documents */
    }
  });

destroy a database

  db.destroy(cb);

fetching a document (GET)

  db.get('vader', function (err, doc) {
      console.log(doc);
  });

If you want to get a specific revision for that document, you can pass it as the 2nd parameter to get().

Cradle is also able to fetch multiple documents if you have a list of ids, just pass an array to get:

  db.get(['luke', 'vader'], function (err, doc) { ... });

Querying a view

  db.view('characters/all', function (err, res) {
      res.forEach(function (row) {
          console.log("%s is on the %s side of the force.", row.name, row.force);
      });
  });

You can access the key and value of the response with forEach using two parameters. An optional third parameter will return the id like this example.

  db.view('characters/all', function (err, res) {
      res.forEach(function (key, row, id) {
          console.log("%s has view key %s.", row.name, key);
      });
  });

To use View Generation Options you can use the view Method with three parameters (viewname, options, callback):

  db.view('characters/all', {group: true, reduce: true} , function (err, res) {
      res.forEach(function (row) {
          console.log("%s is on the %s side of the force.", row.name, row.force);
      });
  });

Querying a row with a specific key

Lets suppose that you have a design document that you've created:

  db.save('_design/user', {
    views: {
      byUsername: {
        map: 'function (doc) { if (doc.resource === 'User') { emit(doc.username, doc) } }'
      }
    }
  });

In CouchDB you could query this view directly by making an HTTP request to:

  /_design/User/_view/byUsername/?key="luke"

In cradle you can make this same query by using the .view() database function:

  db.view('user/byUsername', { key: 'luke' }, function (err, doc) {
      console.dir(doc);
  });

Querying a view with an array key

Say you create view for cars that has an array key with make and model

db.save('_design/cars', {
  views: {
    byMakeAndModel: {
      map: function (doc) {
        if (doc.resource === 'Car' && doc.make && doc.model) {
          var key = [doc.make, doc.model]
          emit(key, doc)
        }
      }
    }
  }
})

If you want all the cars made by Ford with a model name between Rav4 and later (alphabetically sorted). In CouchDB you could query this view directly by making an HTTP request to:

  /_design/User/_view/byMakeAndModel/?startkey=["Ford"]&endkey=["Ford", "\u9999"]

In cradle you can make this same query by using the .view() database function with startkey andendkey options.

var util = require('util')
var opts = {
  startkey: ['Ford'],
  endkey: ['Ford', '\u9999']
}
db.view('cars/', opts, function (err, docs) {
  if (err) {
    util.error(err)
    return
  }
  util.debug(docs)
});

In the options object you can also optionally specify whether or not to group and reduce the output. In this example reduce must be false since there is no reduce function defined for the cars/byMakeAndModel. With grouping and reducing the options object would look like:

var opts = {
  startkey: ['Ford'],
  endkey: ['Ford', '\u9999'],
  group: true,
  reduce: true
}

creating/updating documents

In general, document creation is done with the save() method, while updating is done with merge().

creating with an id (PUT)

  db.save('vader', {
      name: 'darth', force: 'dark'
  }, function (err, res) {
      // Handle response
  });

creating without an id (POST)

  db.save({
      force: 'dark', name: 'Darth'
  }, function (err, res) {
      // Handle response
  });

updating an existing document with the revision

  db.save('luke', '1-94B6F82', {
      force: 'dark', name: 'Luke'
  }, function (err, res) {
      // Handle response
  });

Note that when saving a document this way, CouchDB overwrites the existing document with the new one. If you want to update only certain fields of the document, you have to fetch it first (with get), make your changes, then resave the modified document with the above method.

If you only want to update one or more attributes, and leave the others untouched, you can use the merge()method:

  db.merge('luke', {jedi: true}, function (err, res) {
      // Luke is now a jedi,
      // but remains on the dark side of the force.
  });

Note that we didn't pass a _rev, this only works because we previously saved a full version of 'luke', and thecache option is enabled.

bulk insertion

If you want to insert more than one document at a time, for performance reasons, you can pass an array tosave():

  db.save([
      { name: 'Yoda' },
      { name: 'Han Solo' },
      { name: 'Leia' }
  ], function (err, res) {
      // Handle response
  });

creating views

Here we create a design document named 'characters', with two views: 'all' and 'darkside'.

  db.save('_design/characters', {
      all: {
          map: function (doc) {
              if (doc.name) emit(doc.name, doc);
          }
      },
      darkside: {
          map: function (doc) {
              if (doc.name && doc.force == 'dark') {
                  emit(null, doc);
              }
          }
      }
  });

These views can later be queried with db.view('characters/all'), for example.

Here we create a temporary view. WARNING: do not use this in production as it is extremely slow (use it to test views).

  db.temporaryView({
      map: function (doc) {
        if (doc.color) emit(doc._id, doc);
      }
    }, function (err, res) {
      if (err) console.log(err);
      console.log(res);
  });

Note: If you must use View Generation Options on your temporary view you can use the three parameter version of the temporaryView() Method - similar to the one described above.

creating validation

when saving a design document, cradle guesses you want to create a view, mention views explicitly to work around this.

  db.save('_design/laws', {
    views: {},
    validate_doc_update:
      function (newDoc, oldDoc, usrCtx) {
        if (! /^(light|dark|neutral)$/.test(newDoc.force))
          throw { error: "invalid value", reason:"force must be dark, light, or neutral" }
      }
    }
  });

removing documents (DELETE)

To remove a document, you call the remove() method, passing the latest document revision.

  db.remove('luke', '1-94B6F82', function (err, res) {
      // Handle response
  });

If remove is called without a revision, and the document was recently fetched from the database, it will attempt to use the cached document's revision, providing caching is enabled.

Connecting with authentication and SSL

  var connection = new(cradle.Connection)('https://couch.io', 443, {
      auth: { username: 'john', password: 'fha82l' }
  });

or

  var connection = new(cradle.Connection)('couch.io', 443, {
      secure: true,
      auth: { username: 'john', password: 'fha82l' }
  });

Retry on Connection Issues

For a unreliable connection, you can have non-streaming queries automatically retry:

  var connection = new(cradle.Connection)('couch.io', 443, {
      retries: 3,
      retryTimeout: 30 * 1000
  });

Changes API

For a one-time _changes query, simply call db.changes with a callback:

  db.changes(function (err, list) {
      list.forEach(function (change) { console.log(change) });
  });

Or if you want to see changes since a specific sequence number:

  db.changes({ since: 42 }, function (err, list) {
      ...
  });

The callback will receive the list of changes as an Array. If you want to include the affected documents, simply pass include_docs: true in the options.

Streaming

You can also stream changes, by calling db.changes without the callback. This API uses the excellent followlibrary from IrisCouch:

  var feed = db.changes({ since: 42 });

  feed.on('change', function (change) {
      console.log(change);
  });

In this case, it returns an instance of follow.Feed, which behaves very similarly to node's EventEmitterAPI. For full documentation on the options available to you when monitoring CouchDB with .changes() see the follow documentation.

Attachments

Cradle supports writing, reading, and removing attachments. The read and write operations can be either buffered or streaming

Writing

You can buffer the entire attachment body and send it all at once as a single request. The callback function will fire after the attachment upload is complete or an error occurs

Syntax

db.saveAttachment(idData, attachmentData, callbackFunction)

Example Say you want to save a text document as an attachment with the name 'fooAttachment.txt' and the content 'Foo document text'

var doc = <some existing document>
var id = doc._id
var rev = doc._rev
var idAndRevData = {
  id: id,
  rev: rev
}
var attachmentData = {
  name: 'fooAttachment.txt',
  'Content-Type': 'text/plain',
  body: 'Foo document text'
}
db.saveAttachment(idAndRevData, attachmentData, function (err, reply) {
  if (err) {
    console.dir(err)
    return
  }
  console.dir(reply)
})

Streaming

You can use a read stream to upload the attachment body rather than buffering the entire body first. The callback function will fire after the streaming upload completes or an error occurs

Syntax

var doc = savedDoc // <some saved couchdb document which has an attachment>
var id = doc._id
var rev = doc._rev
var idAndRevData = {
  id: id,
  rev: rev
}
var attachmentData = {
  name: attachmentName               // something like 'foo.txt'
  'Content-Type': attachmentMimeType // something like 'text/plain', 'application/pdf', etc.
  body: rawAttachmentBody            // something like 'foo document body text'
}
var readStream = fs.createReadStream('/path/to/file/')
var writeStream  = db.saveAttachment(idData, attachmentData, callbackFunction)
readStream.pipe(writeStream)

When the streaming upload is complete the callback function will fire

Example Attach a pdf file with the name 'bar.pdf' located at path './data/bar.pdf' to an existing document

var path = require('path')
var fs = require('fs')
// this document should already be saved in the couchdb database
var doc = {
  _id: 'fooDocumentID',
  _rev: 'fooDocumentRev'
}
var idData = {
  id: doc._id,
  rev: doc._rev
}
var filename = 'bar.pdf' // this is the filename that will be used in couchdb. It can be different from your source filename if desired
var filePath = path.join(__dirname, 'data', 'bar.pdf')
var readStream = fs.createReadStream
// note that there is no body field here since we are streaming the upload
var attachmentData = {
  name: 'fooAttachment.txt',
  'Content-Type': 'text/plain'
}
db.saveAttachment(idData, attachmentData, function (err, reply) {
  if (err) {
    console.dir(err)
    return
  }
  console.dir(reply)
}, readStream)

Reading

Buffered

You can buffer the entire attachment and receive it all at once. The callback function will fire after the download is complete or an error occurs. The second parameter in the callback will be the binary data of the attachment

Syntax

db.getAttachment(documentID, attachmentName, callbackFunction)

Example Say you want to read back an attachment that was saved with the name 'foo.txt'

var doc = <some saved document that has an attachment with name *foo.txt*>
var id = doc._id
var attachmentName = 'foo.txt'
db.getAttachment(id, attachmentName, function (err, reply) {
  if (err) {
    console.dir(err)
    return
  }
  console.dir(reply)
})

Streaming

You can stream the attachment as well. If the attachment is large it can be useful to stream it to limit memory consumption. The callback function will fire once the download stream is complete. Note that there is only a single error parameter passed to the callback function. The error is null is no errors occured or an error object if there was an error downloading the attachment. There is no second parameter containing the attachment data like in the buffered read example

Syntax

var readStream = db.getAttachment(documentID, attachmentName, callbackFunction)

Example Say you want to read back an attachment that was saved with the name 'foo.txt'. However the attachment foo.txt is very large so you want to stream it to disk rather than buffer the entire file into memory

var doc = <some saved document that has an attachment with name *foo.txt*>
var id = doc._id
var attachmentName = 'foo.txt'
var downloadPath = path.join(__dirname, 'foo_download.txt')
var writeStream = fs.createWriteStream(downloadPath)
var readStream = db.getAttachment('piped-attachment', 'foo.txt', function (err) { // note no second reply paramter
  if (err) {
    console.dir(err)
    return
  }
  console.dir('download completed and written to file on disk at path', downloadPath)
})
readStream.pipe(writeStream)

Removing

You can remove uploaded attachments with a _id and an attachment name

Syntax

db.removeAttachment(documentID, attachmentName, callbackFunction)

Example Say you want to remove an attachment that was saved with the name 'foo.txt'

var doc = <some saved document that has an attachment with name *foo.txt*>
var id = doc._id
var attachmentName = 'foo.txt'
db.removeAttachment(id, attachmentName, function (err, reply) {
  if (err) {
    console.dir(err)
    return
  }
  console.dir(reply)
})

Other API methods

CouchDB Server level

  new(cradle.Connection)().*

• databases(): Get list of databases
• config(): Get server config
• info(): Get server information
• stats(): Statistics overview
• activeTasks(): Get list of currently active tasks
• uuids(count): Get count list of UUIDs
• replicate(options): Replicate a database.

database level

  new(cradle.Connection)().database('starwars').*

• info(): Database information
• all(): Get all documents
• compact(): Compact database
• viewCleanup(): Cleanup old view data
• replicate(target, options): Replicate this database to target.

Testing

After cloning the repo and installing all dependencies (using npm install) you can run all tests using vows:

$ node test/helpers/seed.js 

$ vows --spec