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https://github.com/emaringolo/pharo-couchdb

Pharo client for CouchDB NoSQL Document Database
https://github.com/emaringolo/pharo-couchdb

Last synced: 16 days ago
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Pharo client for CouchDB NoSQL Document Database

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# Pharo CouchDB Client

![CouchDB](couchdb-vertical-logo.png)



This provides a lightweight Pharo client for [CouchDB NoSQL Document Database](https://couchdb.org) with support for basic JSON documents as well objects serialization/deserialization in JSON format.



The source is based on an [old version](https://cwiki.apache.org/confluence/display/COUCHDB/Smalltalk) for VisualWorks, but this one uses [Zinc](https://github.com/svenvc/Zinc) HTTP client (`ZnClient`), URL objects (`ZnUrl`) instead of plain URL strings, has the `Couch` prefix for the class names (due to the lack of namespaces), and has other refactorings that I considered relevant (although there are many more to do). This version also supports document attachment operations using Base64 encoding for download.



There are several pending features to be added to this client, if you have any issues please create an issue and/or send a pull request.

Or if you need a full-featured, including a native View Server and App Contexts you can use the [SCouchDB Client](https://github.com/jmari/SCouchDB).



# Client Installation

```smalltalk

Metacello new

	baseline: 'CouchDB';

	repository: 'github://eMaringolo/pharo-couchdb/src';

	load.

```



# Server Installation

Download CouchDB and install it [following the instructions in CouchDB website](https://couchdb.apache.org/#download). 



If you install it using defaults, it will a create a default server running at `http://127.0.0.1:5984/` without authentication. All the examples will assume the server is running at that address and port.



# How to use



The current version provides the class `CouchInterface` that will provide control over the server databases.



You can instantiate an interface by evaluating:



```smalltalk

client := CouchInterface url: 'http://127.0.0.1:5984/'.

```



But that above will not attempt any connection to the server. So you can assert whether the server exists you can evaluate:

```smalltalk

client exists

```



Then you can create a database by asking the interface to create a new database.

```smalltalk

database := client create: 'pharodb`

```



If the database was already created you can also instantiate it by evaluating:

```smalltalk

database := CouchDatabase url: 'http://localhost:5984/pharodb'

```



And then, you're ready to store your first document. You can store anything that can be serialized as JSON. 



By default this CouchDB client sends the `#couchJson` message to objects to convert them to a String with JSON syntax that will be stored as the document.



```smalltalk

document := database create: { 'foo' -> true. 'baz' -> (1 to: 5) } asDictionary 

```



This will return a `CouchDocument` that will contain a dynamically assigned `_id` and other information such as the `_rev` number. And more importantly, you can can ask for the URL of the recently created document.



```smalltalk

document url "http://127.0.0.1:5984/pharodb/36557e332476cf324dd0bcc009005801"

```



Then you can copy that URL and paste it in your web browser of preference, and retrieve the contents of the document.



Note: Even when all documents are stored as JSON, when served by CouchDB they are returned as `text/plain`.



A `CouchDocument` works a wrapper for an object, which by default, as in our above example, is a `Dictionary`.



So in our above sample document, we can do:



```

document object at: 'foo' put: false.

document save

```



This will save the created document and also increment the revision number, which you can query by sending `#revision` to the document.



### Document attachments



All documents can have attachments that will get versioned along the document itself. You can add any file as attachment, you can do it directly by passing the file name, the MIME type and the contents, or by instantiating a `CouchAttachment` object.

The contents are expected to be bytes, so encode and decode strings accordingly.



```smalltalk

self 

  saveAttachmentNamed: 'foo.txt'

  mimeType: ZnMimeType textPlain

  contents: 'This is a sample attachment' utf8encoded

```



You can save an attachment with the same name as many times as you want, each time you save it it will increment the revision number of the document.



Every time you query for a `CouchDocument` it will fetch the attached file, but will present them only as stubs without the content.



So, following our example we could do:

```smalltalk

document := CouchDocument url: 'http://127.0.0.1:5984/pharodb/36557e332476cf324dd0bcc009005801'.

document attachments

```



That will return a Dictionary whose keys will be the attachment names and instances of `CouchAttachmentStub` its values. You can send `#download` to an attachment stub to retrieve its full contents.



## Mapping objects



Although it is convenient to serialize/deserialize simple objects such as Dictionaries and Arrays into a JSON representation, the original implementation of the client devised a way to "map" objects to/from JSON using a few extra properties.



If you have the `CouchDB-Examples` package loaded, you'll find the `CouchSofa` and `CouchPillow` example classes, these classes have nothing special, but serve as a reference of how to save/restore an object, with dependencies, from the database.



```smalltalk

database create: CouchSofa example1

```



This will create a regular JSON document for the body, but will add a `+class` property with the name of the Smalltalk class of the mapped object. 



### How mapping works



The basic classes such as `SequenceableCollection`, `Dictionary`, `String`, etc. know how to write themselves as JSON, but other classes must define what attributes must be mapped. This is achieved by means of the `couchDocumentProperties` method.



```smalltalk

CouchSofa>>#couchDocumentProperties 



	^Dictionary new

		at: 'weight' put: #weight;

		at: 'pillows' put: #pillows;

		yourself

```



This Dictionary defines a mapping between a key (that will be used as the property name when serialized as JSON) and a symbol that will work as a getter (sending `asMutator` to be used as setter). This of course could use some more advanced mapping technique or at least better accessors such as those in [Magritte](https://github.com/magritte-metamodel/magritte), but for the most part if works without issues.



The `pillows` accessor returns a collection of `CouchPillow` instances, `CouchPillow` also defines `couchDocumentProperties`, otherwise the instances would be serialized as empty JSON objects and deserialized as empty Dictionaries.



## Remarks

Although this guide is small, it is suggested to use the GT Inspector to "dive" into each message send, because CouchDB objects works as containers in the following sequence "Server" -> "Database" -> "Document" -> "Attachment".