Skip to content

Latest commit

 

History

History
130 lines (104 loc) · 5.09 KB

cjklib.dbconnector.rst

File metadata and controls

130 lines (104 loc) · 5.09 KB
Raw

:mod:`cjklib.dbconnector` --- SQL database access

.. automodule:: cjklib.dbconnector

A DatabaseConnector connects to one or more SQL databases. It provides four simple methods for retrieving scalars or rows of data:

  1. :meth:`~cjklib.dbconnector.DatabaseConnector.selectScalar`: returns one single value
  2. :meth:`~cjklib.dbconnector.DatabaseConnector.selectRow`: returns only one entry with several columns
  3. :meth:`~cjklib.dbconnector.DatabaseConnector.selectScalars`: returns entries for a single column
  4. :meth:`~cjklib.dbconnector.DatabaseConnector.selectRows`: returns multiple entries for multiple columns

This class takes care to load the correct database(s). It provides for attaching further databases and gives any program that depends on cjklib the possibility to easily add own data in databases outside cjklib extending the library's information.

DatabaseConnector has a convenience function :meth:`~cjklib.dbconnector.getDBConnector` that loads an instance with the proper settings for the given project. By default settings for project 'cjklib' are chosen, but this behaviour can be overwritten by passing a different project name: getDBConnector(projectName='My Project'). Connection settings can also be provided manually, omitting automatic searching. Multiple calls with the same connection settings will return the same shared instance.

Example:

>>> from cjklib import dbconnector
>>> from sqlalchemy import select
>>> db = dbconnector.getDBConnector()
>>> db.selectScalar(select([db.tables['Strokes'].c.Name],
...     db.tables['Strokes'].c.StrokeAbbrev == 'T'))
u'\u63d0'

DatabaseConnector is tested on SQLite and MySQL but should support most other database systems through SQLAlchemy.

SQLite and Unicode

SQLite be default only provides letter case folding for alphabetic characters A-Z from ASCII. If SQLite is built against ICU, Unicode methods are used instead for LIKE and upper()/lower(). If ICU is not compiled into the database system :class:`~cjklib.dbconnector.DatabaseConnector` can register own methods. As this has negative impact on performance, it is disabled by default. Compatibility support can be enabled by setting option 'registerUnicode' to True when given as configuration to __init__() or :meth:`~cjklib.dbconnector.getDBConnector` or alternatively can be set as default in cjklib.conf.

Multiple database support

A DatabaseConnector instance is attached to a main database. Further databases can be attached at any time, providing further tables. Tables from the main database will shadow any other table with a similar name. A table not found in the main database will be chosen from a database in the order of their attachment.

The :attr:`~cjklib.dbconnector.DatabaseConnector.tables` dictionary allows simple lookup of table objects by short name, without the need of knowing the full qualified name including the database specifier. Existence of tables can be checked using :meth:`~cjklib.dbconnector.DatabaseConnector.hasTable`; :attr:`~cjklib.dbconnector.DatabaseConnector.tables` will only include table information after the first access. All table names can be retrieved with :meth:`~cjklib.dbconnector.DatabaseConnector.getTableNames`.

Table lookup is designed with a stable data set in mind. Moving tables between databases is not specially supported and while operations through the :mod:`cjklib.build` module will update any information in the :attr:`~cjklib.dbconnector.DatabaseConnector.tables` dictionary, manual creating and dropping of a table or changing its structure will lead to the dictionary having obsolete information. This can be circumvented by deleting keys forcing an update:

>>> del db.tables['my table']

Example:

>>> from cjklib.dbconnector import DatabaseConnector
>>> db = DatabaseConnector({'url': 'sqlite:////tmp/mydata.db',
...     'attach': ['cjklib']})
>>> db.tables['StrokeOrder'].fullname
'cjklib_0.StrokeOrder'

Discovery of attachable databases

DatabaseConnector has the ability to discover databases attaching them to the main database. Specifying databases can be done in three ways:

  1. A full URL can be given denoting a single database, e.g. 'sqlite:////tmp/mydata.db'.
  2. Giving a directory will add any .db file as SQLite database, e.g. '/usr/local/share/cjklib'.
  3. Giving a project name will prompt DatabaseConnector to check for a project config file and add databases specified there and/or scan that project's default directories, e.g. 'cjklib'.

Functions

.. autofunction:: getDBConnector


.. autofunction:: getDefaultConfiguration

Classes

.. currentmodule:: cjklib.dbconnector


.. autoclass:: DatabaseConnector
   :show-inheritance:
   :members:
   :undoc-members:

   .. autoattribute: attached
   .. autoattribute: compatibilityUnicodeSupport
   .. autoattribute: connection
   .. autoattribute: databaseUrl
   .. autoattribute: engine
   .. autoattribute: metadata
   .. autoattribute: DatabaseConnector.tables