Store +Overview

Purpose

It +is often necessary to persist a data structure such as an object by writing +it to memory as a sequence of bytes called a stream. A complex object is persisted +as multiple streams collectively known as a store. The Store component provides +access to stores in Symbian platform.

Required background

The +Store component requires no specific background apart from C++ and Symbian +platform.

Key concepts +and terms

The API has the following key concepts.

stream store: a store consisting of streams, implemented by CStreamStore
persistent store: a store which persists beyond the lifetime of the application which +creates it, implemented by CPersistentStore
embedded store: a store which can itself be stored as a stream in another store, implemented +by CEmbeddedStore
memory store: a store which resides in memory and exists only for the life of the +store object, implemented by CBufStore
dictionary store base and streams: a sequence of streams accessed by a UID, implemented by CDictionaryStore

Architecture

A +stream is a representation of a data structure (such as an object) as a sequence +of bytes. Structures as complex as most applications require multiple streams +to store their state. This is termed a store. Stream types that work with +stores are provided by the Store +Streams API.

The Stores API defines both base classes that +define store abstractions without specifying the storage medium, and some +concrete store types.

The abstract classes are used as the base classes +of separate APIs which use particular storage media. In particular the File Stores API defines +further concrete stores which use file storage. Its base class, CFileStore extends CPersistentStore and +has its own subclasses such as CDirectFileStore. Concrete +store types do not have to provide all the stream manipulation functionality +defined by the base class interfaces: for example, direct file stores do not +support individual deletion of streams within a store.

Dictionary +stores are accessed by a UID whereas stream stores are accessed by a stream +ID. Persistent stores persist beyond the lifetime of the application that +created them: they have a root stream from which the other streams in the +store can be found. Embedded stores can be stored as streams in other stores: +once written they cannot be modified.

Stores are integrated with the +application architecture as defined in the Uikon Core API. That expects file-based +and embedded applications to handle their data storage through stores.

Stores +are also the basis of the relational database provided by DBMS.

+Store inheritance diagram + +

APIs + + + +API +Description + + + + +

CStreamStore

Provides the core abstract framework for stores allowing streams +to be created and manipulated

+ + +

CPersistentStore

Persistent store abstract base class

+ + +

CEmbeddedStore

Encapsulates an embedded store

+ + +

CBufStore

In-memory non-persistent store

+ + +

CDictionaryStore

Dictionary store interface

+ + +

RStoreReadStream

Supports the opening and manipulation of an existing stream in a +store

+ + +

RStoreWriteStream

Supports the writing of a stream to a store

+ + +

RFileBuf

A stream buffer hosted by a file

+ + + +

Typical uses

A +typical use of stores is to write files to memory without using the file server. +This is a good thing to do when an application uses embedded documents.