Introduction +to embedded stores

diff -r 43e37759235e -r 51a74ef9ed63 Symbian3/SDK/Source/GUID-983C5DB9-85EF-541E-B494-19E3E617914A.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/SDK/Source/GUID-983C5DB9-85EF-541E-B494-19E3E617914A.dita Wed Mar 31 11:11:55 2010 +0100 @@ -0,0 +1,44 @@ + + + + + +Introduction +to embedded stores Data contained in a stream can represent a store in its own right +rather than just objects. Such a store is known as an embedded store. +

The stream containing the embedded store is known as the host stream.

It is often convenient, and sometimes necessary, to collect the streams +representing a partial object network into an embedded store. This makes it +easier for the streams representing such a partial object network to be deleted, +by deleting (from the top level store) the stream containing the embedded +store.

The alternative is to traverse the individual streams representing the +partial object network and deleting them in the correct sequence; this can +be difficult.

The following diagram shows the idea:

+ +Embedded store within stream + + +

An embedded store can contain an arbitrarily complex network of streams. +As well as being easy to delete, this stream network can also be copied by +simply copying the host stream from the containing store.

Embedded stores are persistent stores.

The embedded store is constructed on a write stream in its containing store +and, for writing, the embedded store behaves like a direct file store — once +streams within the embedded store have been committed and closed, they cannot +subsequently be changed, i.e. streams cannot be replaced, deleted, extended +or changed in any way.

Embedded stores are used for object embedding by the application architecture. +Because the embedded store behaves like a direct file store, only document +types with direct representations can be embedded. In particular, documents +using permanent-type stores, such as the database or the agenda, cannot be +embedded. Such documents may, however, contain any type of embeddable document.