Perstore is a cross-platform JavaScript object store interface for mapping persistent objects to various different storage mediums using W3C's object store API. Perstore includes JavaScript object-relational mapping for SQL databases, JSON file storage, and hopefully support for many other object/document style storage systems that provide more direct object storage. Perstore provides model classes that wrap data stores, and supports JSON Schema integrity enforcement, link management, and prototype construction. Perstore also provides faceted access to models for an object-capability based security model.
Typical usage of Perstore looks like:
// first setup the object store, here we use SQL/ORM store
var store = require("sql").SQLStore({
type: "mysql",
table: "my_table",
idColumn: "id"
});
// now we can setup a model that wraps the data store
var model = require("model").Model("Example", store, {
properties: {
// we can define optionally define type constraints on properties
foo: String
},
prototype: {
// we can define functions on the prototype of the model objects as well
getFoo: function(){
return this.foo;
}
}
});
// now we can interact with the store and it's objects
var someObject = model.get(someId); // retrieve a persisted object
someObject.getFoo(); // returns the current value of foo
someObject.foo = "bar"; // make a change
someObject.save(); // and save it
model.delete(someOtherId); // delete an object
var facet = require("facet").Restrictive(model, {
});
facet.delete(someId) -> will fail, as the facet has not allowed access to delete().
A model is defined with the Model constructor in the "model" module. A Model definition may follow the JSON schema definition for contractual constraints (usually defining property type constraints in the "properties" property and relations with the "links" property). property. It may also contain a prototype property which defines the prototype object for all instances of the model. Methods can be defined on the prototype object, as well as directly on the model. REST methods such as get, put, and delete are implemented directly on the model, and can be overriden for specific functionality. Perstore roughly follows the class definition structure used by Persevere 1.0
Perstore provides easy to use object persistence mechanism. Persisted model object instances have three default methods:
- save() - Saves any changes that have been made to an object to the data store.
- load() - If the object has not been fully loaded (sometime queries may return partial object), the object will be fully loaded from the data store.
- get(property) - Gets the value of the given property. If the property is a link relation or reference, get() will resolve and load the target object. For simple properties, object.get("prop") and object.prop will yield the same value.
In the initial example, object persistence is demonstrated with the "someObject" variable. The object is loaded (via the get call to the model), modified, and saved (with the save() call).
Facets provide secure, controlled access to models. The facet module comes provides two facet constructors: Permissive and Restrictive. A Permissive facet allows all actions on the model by default. Methods can be defined/overriden in the Permissive definition to control or disable access to certain functionality. A Restrictive facet only allows read access methods by default (get and query). One can define/override methods to allow explicit access to other methods such as put or create. An example facet that only allows read access and creation of new objects:
var facet = require("facet").Restrictive(model, {
create: function(object){ // allow create
return model.create(object);
}
});
Models wrap data stores, which provide the low level interaction with the database or storage system. Perstore comes with several data stores including (in the store directory):
- sql - An SQL-based object store. This stores and retrieves objects as rows in databases. Currently this only fully implemented in Rhino, but the sql data store can easily wrap an SQL database provider that simple provides an W3C SQL database style executeSql(sql) function.
- memory - An in-memory data store. None of the data in this store will be persisted
- js-file - Reads and stores all data in the store from a JSON (with JS extensions for dates and other non-standard JSON types) file.
- remote - This can connect to a remote HTTP/REST based JSON server to store and retrieve data.
Perstore also includes several store wrappers that can be used to compose more sophisticate stores by adding functionality (also in the store directory):
- cache - Adds in-memory caching support to a provided store
- aggregate - Combines record data from multiple stores into a single object store
- replicated - Provides data replication across multiple stores
- full-text - Adds full text indexing (currently only available in Rhino through Lucene)
- inherited - Provides a super-sub type relationship between data stores
The following is store API for Perstore. The same API is used for data stores, store models, and facets. All of the functions are optional. If they do not exist, it indicates that the store or model does not support or allow the said functionality. All of the functions may return a promise instead of the actual return value if they require asynchronous processing to complete the operation. They are roughly listed in order of importance (get(id) is the most important function):
get(id) - Finds the persisted record with the given identifier from the store and returns an object representation (should always be a new object).
put(object, id) - Stores the given object in storage. The record may or may not already exist. The optional second parameter defines the primary identifier for storing the object. If the second parameter is omitted, the key may be specified the primary identifier property. If that is not specified, the key may be auto-generated. The primary identifer for the object should be returned
delete(id) - Deletes the record with the given identifier from the store.
query(queryString, options) - This executes a query against the data store. The queryString parameter defines the actual query, and the options parameter should be an object that provides extra information. The following properties on the options object may be included:
- start - The offset index to start at in the result set
- end - The offset index to end at in the result set
- parameters - An array of values for parameterized queries
The function should generally return an array representing the result set of the query (unless the query creates a single aggregate object or value). While there is no normative definition of the query language, the query method SHOULD support URL encoded queries like:
foo=value&bar=2
More extensive query syntax can be based on the discussions here. Implementors are encouraged to utilize the resource-query module in perstore for parsing queries into a query AST-style structured object for ease of use.
create(object) - Stores a new record. This acts similar to put, but should only be called when the record does not already exist. Stores do not need to implement this method, but may implement for ease of differentiating between creation of new records and updates. This should return the identifier of the newly create record.
subscribe(resource, callback) - Subscribes to changes in the given resource or set of resources. The callback is called whenever data is changed in the monitored resource(s).
transaction() - If it exists, this is called when a transaction is started. This should return a transaction object with the following two functions:
- commit() - This is called when a transaction is committed.
- abort() - This is called when a transaction is aborted.
Perstore is designed to allow easy construction of new data stores. A data store in Perstore is a JavaScript object with any or all of the functions defined above.
Perstore is part of the Persevere project, and therefore is licensed under the AFL or BSD license. The Persevere project is administered under the Dojo foundation, and all contributions require a Dojo CLA.
See the main Persevere project for more information: