The Python Connection Class

The Connection class provides the following methods to manage the database Connection, Transactions and Cursors:

close()

Close this connection; the connection object becomes invalid

startTransaction(type, priority)

Start a database transaction on this connection

commit()

Commit an open transaction on this connection

rollback()

Rollback the database changes made in the current transaction

createBackup(filename, label, type, compression_level, cipher)

Create an incremental backup record in the specified file

restoreBackup(filename, label, cipher)

Restore the database from an incremental backup in the specified file up to the specified label

deleteAll(clsDesc)

Delete all objects of the class clsDesc (the class description, either as a string or the class type taken from the Dictionary object) For example, the following two calls are equivalent:

 
    >>>conn.deleteAll(‘myclass’)
 
    >>>conn.deleteAll(dict.classes[‘myclass’])

 

new(clsName)

Create new object in the database using the schema definition for class clsName

waitEvent(eventId)

Start waiting for an asynchronous event specified by argument eventId (Normally this is called from a separate event-handler thread)

releaseAllEvents()

Release all events and stop the event handler threads

remove(obj)

Remove an object obj from the database. The object argument obj must be taken from one of the Cursor operations find() or search() executed on this connection

cursor(cls, idx)

Create a cursor for retrieving data on this connection

getStats()

Get database statistics; it returns a dictionary containing keys with the following database information:

 
    TotalPages
    FreePages
    PageSize
 

For persistent databases it also contains dictionary keys with the disk file statistics:

 
    DataFileSize
    LogFileSize
    UsedDatabaseSize
 

getClassStats(cls)

Get class cls statistics from the database; iIt returns a dictionary containing the following keys:

 
    ObjectsNum
    VersionsNum
    CorePages
    BlobPages
    CoreSpace
 

getIndexStats(idx)

Get index idx statistics from the database; it returns a dictionary containing the following keys:

 
    ClassCode
    Type
    Label
    KeysNum
    PagesNum
    AvgChainLength – for hash indexes only
    MaxChainLength - for hash indexes only
    LevelsNum – for tree indexes only
    DuplicatesNum  - for tree indexes only
    DiskPagesNum
 

getDiskCacheInfo()

Get disk cache statistics; it returns a dictionary containing the following keys:

     
    connection_cache_hits
    cache_hits
    cache_misses
    allocated_pages
    used_pages
    pinned_pages
    modified_pages
    dirty_pages
    copied_pages
    write_delayed_pages
    subsequent_reads
 

saveSnapshot(path, saveMetadata=True, saveCRC=True)

Perform a snapshot image of the database to a disk file specified by path arguments

db

A Read-Only property specifying the database on which this connection is opened

engine

A Read-Only property specifying the SQL engine for this connection