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Persist Objects

When it comes to persistence you have to deal with sessions and transactions. You have to create a session for a specific database and wrap a transaction around your insertions or modifications.

After created a session objects you can either create the database schema ...

// the object store
object_store ostore;
// configure object store
// ...
// create and open a session
oos::session ses(ostore, "sqlite://person.db");
// create the database schema
ses.create();

... or load the data from database.

// load the data from database

ses.load();

Once the schema is created or the data is loaded you can start and insert, update or delete your data. Therefor create a transaction object with the current session and start the transaction by calling oos::transaction::begin(). After completing your modifications call oos::transaction::commit() to commit all your modifications to the database. If in error occurred while doing your modifications catch the exception. In the catch block you can call oos::transaction::rollback() to rollback all your modifications.

// create a transaction for session
oos::transaction tr(ses);
try {
  // begin the transaction
  tr.begin();
  // insert some objects
  ostore.insert(new person("joe", 45))
  ostore.insert(new person("walter", 56));
  ostore.insert(new person("helen", 37));
  ostore.insert(new person("tim", 14));
  // commit the modifications
  tr.commit();
} catch (exception &ex) {
  // on error rollback transactions
  tr.rollback();
}

Supported Databases

There're currently three supported databases and the in memory database. But more databases will follow. Next is the description of the database connection string for the supported databases.

MS SQL Server

// MSSQL connection string with password
session ses(ostore, "mssql://user:passwd@host/db");
// MSSQL connection string without password
session ses(ostore, "mssql://user@host/db");

MySQL

// MySQL connection string with password
session ses(ostore, "mysql://user:passwd@host/db");
// MySQL connection string without password
session ses(ostore, "mysql://user@host/db");

SQLite

// MySQL connection string

session ses(ostore, "sqlite://database.sqlite");

Relations on Database

In short: All kinds of supported relations (list, vector and linked_list) are working out of the box. You don't have to worry about saving and loading relations.

The long description: When loading a relation from database at least two object types/tables are involved the parent and the children. With theses two participans we deal with two scenarios: The parent is loaded before its children and the children are loaded first.

Scenario 1: Parents are loaded first. Everything is fine. We mark the parent as loaded and when the children table is loaded all parent objects can be filled with their children.

Scenario 2: Children are loaded first. Because the parents aren't available placeholders with their ids are created from the id stored in the concrete children. Furthermore temporary lists are build up holding all children for each parent. When finally the parents are loaded these lists are used to the concrete parent container.

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