en database connect

jActiveRecord provides DB.open static method, which parameters are compatible with java.sql.DriverManager#getConnection, to connect database. Returns me.zzp.ar.DB instance if success; otherwise, throw a me.zzp.ar.ex.DBOpenException exception.

• open(String url): Attempts to establish a connection to the given database URL.
• open(String url, String username, String password): Attempts to establish a connection to the given database URL with username and password.
• open(String url, Properties info): Attempts to establish a connection to the given database URL with connection information.

Note above three methods would create an inner database connection only, so that works with in-memory database well; While should use C3P0 pooled connection for better performance in real project.

DB sqlite3 = DB.open("jdbc:sqlite::memory:");
DB postgresql = DB.open("jdbc:postgresql:test", "postgres", "password");
DB mysql = DB.open("jdbc:mysql://localhost/test", new Properties());