persistence.js

persistence.js is a asynchronous Javascript object-relational
mapper library. It can be used both in the web browser and on
the server using node.js. It currently
supports 4 types of data stores:

• HTML5 WebSQL database, a
  somewhat controversial part of HTML5 that is supported in Webkit
  browsers, specifically on mobile devices, including iPhone, Android
  and Palm’s WebOS.
• Google Gears, a browser plug-in that adds
  a number of feature to the browser, including a in-browser database.
• MySQL, using the
  node-mysql, node.js module
  on the server.
• In-memory, as a fallback. Keeps the database in memory and is
  cleaned upon a page refresh (or server restart), unless saved to
  localStorage.

There is also an experimental support for Qt 4.7 Declarative UI
framework
(QML) which
is an extension to JavaScript.

For browser use, persistence.js has no dependencies on any other
frameworks, other than the Google Gears initialization
script, in case you
want to enable Gears support.

Plug-ins

There are a few persistence.js plug-ins available that add functionality:

• persistence.search.js, adds simple full-text search capabilities,
  see docs/search.md for more information.
• persistence.migrations.js, supports data migrations (changes to
  the database schema), see docs/migrations.md for more information.
• persistence.sync.js, supports database synchronization with a
  remote server, see docs/sync.md for more information.
• jquery.persistence.js, adds jQuery integration, including
  jQuery-mobile ajax request interception and re-routing to persistencejs,
  see docs/jquery.md for more information and demo/jquerymobile for a
  simple demo.

A Brief Intro to Async Programming

In browsers, Javascript and the web page’s rendering engine share
a single thread. The result of this is that only one thing can happen
at a time. If a database query would be performed synchronously,
like in many other programming environments like Java and PHP the
browser would freeze from the moment the query was issued until the
results came back. Therefore, many APIs in Javascript are defined as
asynchronous APIs, which mean that they do not block when an
“expensive” computation is performed, but instead provide the call
with a function that will be invoked once the result is known. In the
meantime, the browser can perform other duties.

For instance, a synchronous database call call would look as follows:

var results = db.query("SELECT * FROM Table");
for(...) { ... }

The execution of the first statement could take half a second, during
which the browser doesn’t do anything else. By contrast, the
asynchronous version looks as follows:

db.query("SELECT * FROM Table", function(results) {
  for(...) { ... }
});

Note that there will be a delay between the db.query call and the
result being available and that while the database is processing the
query, the execution of the Javascript continues. To make this clear,
consider the following program:

db.query("SELECT * FROM Table", function(results) {
  console.log("hello");
});
console.log("world");

Although one could assume this would print “hello”, followed by
“world”, the result will likely be that “world” is printed before
“hello”, because “hello” is only printed when the results from the
query are available. This is a tricky thing about asynchronous
programming that a Javascript developer will have to get used to.

Using persistence.js in the browser

Browser support

• Modern webkit browsers (Google Chrome and Safari)
• Firefox (through Google Gears)
• Opera
• Android browser (tested on 1.6 and 2.x)
• iPhone browser (iPhone OS 3+)
• Palm WebOS (tested on 1.4.0)
• Other browsers supporting localStorage (e.g. Firefox)

(The following is being worked on:)
Internet Explorer is likely not supported (untested) because it
lacks __defineGetter__ and __defineSetter__ support, which
persistence.js uses heavily. This may change in IE 9.

Setting up

• Using bower:

bower install persistence

Add a <script> to your index.html:

lib/persistence.js needs to be added, as well as any data stores you want to use. Note that the mysql and
websql stores both depend on the sql store. A typical setup requires you to add at least
lib/persistence.js, lib/persistence.store.sql.js and lib/persistence.store.websql.js as follows:

<script src="/bower_components/persistencejs/lib/persistence.js"></script>
<script src="/bower_components/persistencejs/lib/persistence.store.sql.js"></script>
<script src="/bower_components/persistencejs/lib/persistence.store.websql.js"></script>

If you want to use the in-memory store (in combination with
localStorage) you also need the persistence.store.memory.js
included.

• Using directly from source:

  git clone git://github.com/zefhemel/persistencejs.git

Copy directories you will need following almost the same instructions above.

Setup your database

You need to explicitly configure the data store you want to use,
configuration of the data store is store-specific. The WebSQL store
(which includes Google Gears support) is configured as follows:

persistence.store.websql.config(persistence, 'yourdbname', 'A database description', 5 * 1024 * 1024);

The first argument is always supposed to be persistence. The second
in your database name (it will create it if it does not already exist,
the third is a description for you database, the last argument is the
maximum size of your database in bytes (5MB in this example).

Setting up for Cordova with SQLitePlugin/WebSQL

Use following if you want to use persistencejs in a Cordova mobile app and you plan to use the Cordova SQLitePlugin:

persistence.store.cordovasql.config(
  persistence,
  'yourdbname',
  '0.0.1',                // DB version
  'My database',          // DB display name
  5 * 1024 * 1024,        // DB size (WebSQL fallback only)
  0,                      // SQLitePlugin Background processing disabled
  2                       // DB location (iOS only), 0 (default): Documents, 1: Library, 2: Library/LocalDatabase
                          //   0: iTunes + iCloud, 1: NO iTunes + iCloud, 2: NO iTunes + NO iCloud
                          //   More information at https://github.com/litehelpers/Cordova-sqlite-storage#opening-a-database
);

For more information on the SQLitePlugin background processing please refer to the SQLitePlugin readme.

The Cordova support in persistencejs will try to work with the SQLitePlugin if it is loaded; if not it will automatically fall back to WebSQL.

Please note that to use Cordova store, you must use the master branch, because it is not included up to release v0.3.0.

The in-memory store

The in-memory store is offered as a fallback for browsers that do not
support any of the other supported stores (e.g. WebSQL or Gears). In
principal, it only keeps data in memory, which means that navigating
away from the page (including a reload or tab close) will result in
the loss of all data.

A way around this is using the persistence.saveToLocalStorage and
persistence.loadFromLocalStorage functions that can save the entire
database to the localStorage, which
is persisted indefinitely (similar to WebSQL).

If you’re going to use the in-memory store, you can configure it as follows:

persistence.store.memory.config(persistence);

Then, if desired, current data can be loaded from the localStorage using:

persistence.loadFromLocalStorage(function() {
  alert("All data loaded!");
});

And saved using:

persistence.saveToLocalStorage(function() {
  alert("All data saved!");
});

Drawbacks of the in-memory store:

• Performance: All actions that are typically performed by a database
  (sorting, filtering), are now all performed in-memory using
  Javascript.
• Limited database size: Loading and saving requires serialization of
  all data from and to JSON, which gets more expensive as your dataset
  grows. Most browsers have a maximum size of 5MB for localStorage.
• Synchronous behavior: Although the API is asynchronous, all
  persistence actions will be performed synchronously on the main
  Javascript thread, which may make the browser less responsive.

Schema definition

A data model is declared using persistence.define. The following two
definitions define a Task and Category entity with a few simple
properties. The property types are based on SQLite
types, specifically supported
types are (but any SQLite type is supported):

• TEXT: for textual data
• INT: for numeric values
• BOOL: for boolean values (true or false)
• DATE: for date/time value (with precision of 1 second)
• JSON: a special type that can be used to store arbitrary
  JSON data. Note that this data can not be used
  to filter or sort in any sensible way. If internal changes are made to a JSON
  property, persistence.js may not register them. Therefore, a manual
  call to anObj.markDirty('jsonPropertyName') is required before calling
  persistence.flush.

Example use:

var Task = persistence.define('Task', {
  name: "TEXT",
  description: "TEXT",
  done: "BOOL"
});

var Category = persistence.define('Category', {
  name: "TEXT",
  metaData: "JSON"
});

var Tag = persistence.define('Tag', {
  name: "TEXT"
});

The returned values are constructor functions and can be used to
create new instances of these entities later.

It is possible to create indexes on one or more columns using
EntityName.index, for instance:

Task.index('done');
Task.index(['done', 'name']);

These indexes can also be used to impose unique constraints :

Task.index(['done', 'name'],{unique:true});

Relationships between entities are defined using the constructor
function’s hasMany call:

// This defines a one-to-many relationship:
Category.hasMany('tasks', Task, 'category');
// These two definitions define a many-to-many relationship
Task.hasMany('tags', Tag, 'tasks');
Tag.hasMany('tasks', Task, 'tags');

The first statement defines a tasks relationship on category objects
containing a QueryCollection (see the section on query collections
later) of Tasks, it also defines an inverse relationship on Task
objects with the name category. The last two statements define a
many-to-many relationships between Task and Tag. Task gets a
tags property (a QueryCollection) containing all its tags and vice
versa, Tag gets a tasks property containing all of its tasks.

The defined entity definitions are synchronized (activated) with the
database using a persistence.schemaSync call, which takes a callback
function (with a newly created transaction as an argument), that is called
when the schema synchronization has completed, the callback is
optional.

persistence.schemaSync();
// or
persistence.schemaSync(function(tx) { 
  // tx is the transaction object of the transaction that was
  // automatically started
});

There is also a migrations plugin you can check out, documentation can be found
in docs/migrations.md file.

Mix-ins

You can also define mix-ins and apply them to entities of the model.

A mix-in definition is similar to an entity definition, except using
defineMixin rather than just define. For example:

var Annotatable = persistence.defineMixin('Annotatable', {
  lastAnnotated: "DATE"
});

You can define relationships between mix-in and entities. For example:

// A normal entity
var Note = persistence.define('Note', {
  text: "TEXT"
});

// relationship between a mix-in and a normal entity
Annotatable.hasMany('notes', Note, 'annotated');

Once you have defined a mix-in, you can apply it to any entity of your model,
with the Entity.is(mixin) method. For example:

Project.is(Annotatable);
Task.is(Annotatable);

Now, your Project and Task entities have an additional lastAnnotated property.
They also have a one to many relationship called notes to the Note entity.
And you can also traverse the reverse relationship from a Note to its annotated object.

Note that annotated is a polymorphic relationship as it may yield either a Project
or a Task (or any other entity which is `Annotatable’).

Note: Prefetch is not allowed (yet) on a relationship that targets a mixin. In the example above
you cannot prefetch the annotated relationship when querying the Note entity.

Notes: this feature is very experimental at this stage. It needs more testing.
Support for “is a” relationships (classical inheritance) is also in the works.

Creating and manipulating objects

New objects can be instantiated with the constructor functions.
Optionally, an object with initial property values can be passed as
well, or the properties may be set later:

var task = new Task();
var category = new Category({name: "My category"});
category.metaData = {rating: 5};
var tag = new Tag();
tag.name = "work";

Many-to-one relationships are accessed using their specified name, e.g.:
task.category = category;

One-to-many and many-to-many relationships are access and manipulated
through the QueryCollection API that will be discussed later:

task.tags.add(tag);
tasks.tags.remove(tag);
tasks.tags.list(tx, function(allTags) { console.log(allTags); });

Persisting/removing objects

Similar to hibernate, persistence.js
uses a tracking mechanism to determine which objects’ changes have to
be persisted to the database. All objects retrieved from the database
are automatically tracked for changes. New entities can be tracked to
be persisted using the persistence.add function:

var c = new Category({name: "Main category"});
persistence.add(c);
for ( var i = 0; i < 5; i++) {
  var t = new Task();
  t.name = 'Task ' + i;
  t.done = i % 2 == 0;
  t.category = c;
  persistence.add(t);
}

Objects can also be removed from the database:

persistence.remove(c);

All changes made to tracked objects can be flushed to the database by
using persistence.flush, which takes a transaction object and
callback function as arguments. A new transaction can be started using
persistence.transaction:

persistence.transaction(function(tx) {
  persistence.flush(tx, function() {
    alert('Done flushing!');
  });
});

For convenience, it is also possible to not specify a transaction or
callback, in that case a new transaction will be started
automatically. For instance:

persistence.flush();
// or, with callback
persistence.flush(function() {
  alert('Done flushing');
});

Note that when no callback is defined, the flushing still happens
asynchronously.

Important: Changes and new objects will not be persisted until you
explicitly call persistence.flush(). The exception to this rule is
using the list(...) method on a database QueryCollection, which also
flushes first, although this behavior may change in the future.

Dumping and restoring data

The library supports two kinds of dumping and restoring data.

persistence.dump can be used to create an object containing a full
dump of a database. Naturally, it is adviced to only do this with
smaller databases. Example:

persistence.dump(tx, [Task, Category], function(dump) {
  console.log(dump);
});

The tx is left out, a new transaction will be started for the
operation. If the second argument is left out, dump defaults
to dumping all defined entities.

The dump format is:

{"entity-name": [list of instances],
 ...}

persistence.load is used to restore the dump produced by
persistence.dump. Usage:

persistence.load(tx, dumpObj, function() {
  alert('Dump restored!');
});

The tx argument can be left out to automatically start a new
transaction. Note that persistence.load does not empty the database
first, it simply attempts to add all objects to the database. If
objects with, e.g. the same ID already exist, this will fail.

Similarly, persistence.loadFromJson and persistence.dumpToJson
respectively load and dump all the database’s data as JSON strings.

Entity constructor functions

The constructor function returned by a persistence.define call
cannot only be used to instantiate new objects, it also has some
useful methods of its own:

• EntityName.all([session]) returns a query collection containing
  all
  persisted instances of that object. The session argument is
  optional and only required when persistence.js is used in
  multi-session mode.
• EntityName.load([session], [tx], id, callback) loads an particular
  object from the database by id or returns null if it has not been
  found.
• EntityName.findBy([session], [tx], property, value, callback) searches
  for a particular object based on a property value (this is assumed to
  be unique), the callback function is called with the found object or
  null if it has not been found.
• EntityName.index([col1, col2, ..., colN], options) creates an index on a column
  of a combination of columns, for faster searching. If options.unique is true,
  the index will impose a unique constraint on the values of the columns.

And of course the methods to define relationships to other entities:

• EntityName.hasMany(property, Entity, inverseProperty) defines a
  1:N or N:M relationship (depending on the inverse property)
• EntityName.hasOne(property, Entity) defines a 1:1 or N:1
  relationship

Entity objects

Entity instances also have a few predefined properties and methods you
should be aware of:

• obj.id, contains the identifier of your entity, this is a
  automatically generated (approximation of a) UUID. You should
  never write to this property.
• obj.fetch(prop, callback), if an object has a hasOne
  relationship to another which has not yet been fetched from the
  database (e.g. when prefetch wasn’t used), you can fetch in manually
  using fetch. When the property object is retrieved the callback function
  is invoked with the result, the result is also cached in the entity
  object itself.
• obj.selectJSON([tx], propertySpec, callback), sometime you need to extract
  a subset of data from an entity. You for instance need to post a
  JSON representation of your entity, but do not want to include all
  properties. selectJSON allows you to do that. The propertySpec
  arguments expects an array with property names. Some examples:
  • ['id', 'name'], will return an object with the id and name property of this entity
  • ['*'], will return an object with all the properties of this entity, not recursive
  • ['project.name'], will return an object with a project property which has a name
    property containing the project name (hasOne relationship)
  • ['project.[id, name]'], will return an object with a project property which has an
    id and name property containing the project name (hasOne relationship)
  • ['tags.name'], will return an object with an array tags property containing
    objects each with a single property: name

Query collections

A core concept of persistence.js is the QueryCollection. A
QueryCollection represents a (sometimes) virtual collection that can
be filtered, ordered or paginated. QueryCollections are somewhate
inspired by Google AppEngine’s Query
class.
A QueryCollection has the following methods:

• filter(property, operator, value)
  Returns a new QueryCollection that adds a filter, filtering a
  certain property based on an operator and value. Supported operators
  are ‘=’, ‘!=’, ‘<’, ‘<=’, ‘>’, ‘>=’, ‘in’ and ‘not in’. Example:
  .filter('done', '=', true)
• or(filter)
  Returns a new QueryCollection that contains items either matching
  the filters specified before calling or, or the filter represented
  in the argument. The filter argument is of a Filter type, there
  are three types of filters:
  • persistence.PropertyFilter, which filters on properties (internally called when filter(...) is used.
    Example: new persistence.PropertyFilter('done', '=', true)
  • persistence.AndFilter, which is passed two filter objects as arguments, both of which should be true.
    Example: new persistence.AndFilter(new persistence.PropertyFilter('done', '=', true), new persistence.PropertyFilter('archived', '=', true))
  • persistence.OrFilter, which is passed two filter objects as arguments, one of which should be true.
    Example: new persistence.OrFilter(new persistence.PropertyFilter('done', '=', true), new persistence.PropertyFilter('archived', '=', true))
• and(filter)
  same as or(filter) except that both conditions should hold for items to be in the collection.
• order(property, ascending)
  Returns a new QueryCollection that will order its results by the
  property specified in either an ascending (ascending === true) or
  descending (ascending === false) order.
• limit(n)
  Returns a new QueryCollection that limits the size of the result
  set to n items. Useful for pagination.
• skip(n)
  Returns a new QueryCollection that skips the first n results.
  Useful for pagination.
• prefetch(rel)
  Returns a new QueryCollection that prefetches entities linked
  through relationship rel, note that this only works for one-to-one
  and many-to-one relationships.
• add(obj)
  Adds object obj to the collection.
• remove(obj)
  Removes object obj from the collection.
• list([tx], callback)
  Asynchronously fetches the results matching the formulated query.
  Once retrieved, the callback function is invoked with an array of
  entity objects as argument.
• each([tx], eachCallback)
  Asynchronously fetches the results matching the formulated query.
  Once retrieved, the eachCallback function is invoked on each
  element of the result objects.
• forEach([tx], eachCallback)
  Alias for each
• one([tx], callback)
  Asynchronously fetches the first element of the collection, or null if none.
• destroyAll([tx], callback)
  Asynchronously removes all the items in the collection. Important: this does
  not only remove the items from the collection, but removes the items themselves!
• count([tx], callback)
  Asynchronously counts the number of items in the collection. The arguments passed
  to the callback function is the number of items.

Query collections are returned by:

• EntityName.all(), e.g. Task.all()
• one-to-many and many-to-many relationships, e.g. task.tags

Example:

var allTasks = Task.all().filter("done", '=', true).prefetch("category").order("name", false).limit(10);
    
allTasks.list(null, function (results) {
    results.forEach(function (r) {
        console.log(r.name)
        window.task = r;
    });
});

Using persistence.js on the server

Installing persistence.js on node is easy using npm:

npm install persistencejs

Sadly the node.js server environment requires slight changes to
persistence.js to make it work with multiple database connections:

• A Session object needs to be passed as an extra argument to
  certain method calls, typically as a first argument.
• Methods previously called on the persistence object itself are now
  called on the Session object.

An example node.js application is included in test/node-blog.js.

Setup

You need to require two modules, the persistence.js library itself
and the MySQL backend module.

var persistence = require('persistencejs');
var persistenceStore = persistence.StoreConfig.init(persistence, { adaptor: 'mysql' });

Then, you configure the database settings to use:

persistenceStore.config(persistence, 'localhost', 3306, 'dbname', 'username', 'password');

Subsequently, for every connection you handle (assuming you’re
building a sever), you call the persistenceStore.getSession()
method:

var session = persistenceStore.getSession();

This session is what you pass around, typically together with a
transaction object. Note that currently you can only have one
transaction open per session and transactions cannot be nested.

session.transaction(function(tx) {
  ...
});

Commit and Rollback

persistence.js works in autocommit mode by default.

You can override this behavior and enable explicit commit and rollback
by passing true as first argument to persistence.transaction.
You can then use the following two methods to control the transaction:

• transaction.commit(session, callback) commits the changes.
• transaction.rollback(session, callback) rollbacks the changes.

Typical code will look like:

session.transaction(true, function(tx) {
  // create/update/delete objects
  modifyThings(session, tx, function(err, result) {
    if (err) {
      // something went wrong
      tx.rollback(session, function() {
        console.log('changes have been rolled back: ' + ex.message);
      });
    }
    else {
      // success
      tx.commit(session, function() {
        console.log('changes have been committed: ' result);
    });
  });
});

Explicit commit and rollback is only supported on MySQL (server side)
for now.

Defining your data model

Defining your data model is done in exactly the same way as regular persistence.js:

var Task = persistence.define('Task', {
  name: "TEXT",
  description: "TEXT",
  done: "BOOL"
});

A schemaSync is typically performed as follows:

session.schemaSync(tx, function() {
  ...
});

Creating and manipulating objects

Creating and manipulating objects is done much the same way as with
regular persistence.js, except that in the entity’s constructor you
need to reference the Session again:

var t = new Task(session);
...
session.add(t);

session.flush(tx, function() {
  ...
});

Query collections

Query collections work the same way as in regular persistence.js
with the exception of the Entity.all() method that now also requires
a Session to be passed to it:

Task.all(session).filter('done', '=', true).list(tx, function(tasks) {
  ...
});

Closing the session

After usage, you need to close your session:

session.close();

Bugs and Contributions

If you find a bug, please report
it. or fork the
project, fix the problem and send me a pull request. For a list of
planned features and open issues, have a look at the issue
tracker.

For support and discussion, please join the persistence.js Google
Group.

Thanks goes to the people listed in AUTHORS for their contributions.

If you use GWT (the Google Web
Toolkit), be sure to have a look at Dennis Z. Jiang’s GWT persistence.js
wrapper

License

This work is licensed under the MIT license.

Support this work

You can support this project by flattering it: