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توضیحات

Django model fields designed to more precisely and semantically define data types.

ویژگی	مقدار
سیستم عامل	-
نام فایل	django-forcedfields-1.0.1
نام	django-forcedfields
نسخه کتابخانه	1.0.1
نگهدارنده	[]
ایمیل نگهدارنده	[]
نویسنده	monotonee
ایمیل نویسنده	monotonee@tuta.io
آدرس صفحه اصلی	https://github.com/monotonee/django-forcedfields
آدرس اینترنتی	https://pypi.org/project/django-forcedfields/
مجوز	MIT

################### django-forcedfields ################### .. image:: https://img.shields.io/pypi/v/django-forcedfields.svg :target: https://pypi.python.org/pypi/django-forcedfields :align: left .. image:: https://travis-ci.org/monotonee/django-forcedfields.svg?branch=master :target: https://travis-ci.org/monotonee/django-forcedfields :align: right ******* Summary ******* A Python module that provides a set of custom, specialized Django model fields. While I haved worked with Django's ORM for some time and have enjoyed many of its features for simple use cases, I find myself increasingly impeded, annoyed, and dissatisfied by its limitations in complex applications. One glaring problem in my eyes is the ORM's lack of semantic database field data types and modifiers. For example, an eight-character varchar field that can be null and that has a default value of "elegy" will *not* result in the MySQL `DDL <https://dev.mysql.com/doc/refman/en/glossary.html#glos_ddl>`_:: VARCHAR(8) DEFAULT 'elegy' NULL but simply as:: VARCHAR(8) NULL While this varchar example may not be the most egregious, it nonetheless illustrates the almost complete reliance upon the application and its ORM for behavior that should be handled, and indeed is best handled, by the database management system itself. Databases should be as self-documenting and semantic as possible, independent of any application code, ORM models, or documentation. I will not compromise this principle for the sake of an ORM's conveniences. To this end, I have begun to create these custom Django model fields to force Django to issue the most specific and complete DDL statements possible. It is my goal with these and future fields to shift responsibility from the application ORM to the underlying database wherever possible while maintaining a consistent and complete ORM interface and database backend abstraction. ************ Installation ************ :: pip install [--user] django-forcedfields ************* Example Usage ************* :: import django_forcedfields as forcedfields or:: from django_forcedfields import TimestampField ****** Fields ****** FixedCharField ============== **class FixedCharField(max_length=None, **options)** This field extends Django's `CharField <https://docs.djangoproject.com/en/dev/ref/models/fields/#charfield>`_. This field inherits all functionality and interfaces from Django's standard CharField but, rather than producing a ``VARCHAR`` field in the database, the FixedCharField creates a ``CHAR`` field. The parent CharField class' keyword argument ``max_length`` is retained and, when passed, specifies the ``CHAR`` field's max length just like it does for the ``VARCHAR`` implementation. The ``CHAR`` data type is supported on all RDBMS in common use with Django. In addition, if a FixedCharField on a model is not given an explicit value and no default field value has been explicitly defined, a ``NULL`` value will be inserted on Model.save(). This is in contrast to Django's standard CharField which incorrectly attempts to insert an empty string in such a case. Ideally, with no explicit value and no default value, an integrity error would be raised by the database but Django's ORM absolutely requires a value for all fields in ``INSERT`` operations. It is impossible to simply omit a database column's value in an ``INSERT`` statement. A note here on Django's `admonition on null values with text fields <https://docs.djangoproject.com/en/dev/ref/models/fields/#null>`_: Django is wrong. ``NULL`` means unknown data, an empty string means an empty string. Their meanings are *semantically different* by definition. Set ``null=True`` on text fields when your use case warrants it. That is, when you may have a complete absence of data as well as the need to record an empty string. Google this topic for more analysis. TimestampField ============== **class TimestampField(auto_now=False, auto_now_add=False, auto_now_update=False, **options)** This field extends Django's `DateTimeField <https://docs.djangoproject.com/en/dev/ref/models/fields/#datetimefield>`_. This field supports all `DateTimeField keyword arguments <https://docs.djangoproject.com/en/dev/ref/models/fields/#datefield>`_ and adds a new ``auto_now_update`` argument. **TimestampField.auto_now_update** ``auto_now_update`` is a boolean that, when True, sets a new timestamp field value on update operations *only*, not on insert. This option is mutually exclusive with ``auto_now``. **Warning:** When using the MySQL backend, the database ``TIMESTAMP`` field will also be updated when ``auto_now`` or ``auto_now_update`` is enabled and when calling QuerySet.update(). In constrast, Django's DateField and DateTimeField only set current timestamp under ``auto_now`` `when calling Model.save() <https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.DateField.auto_now>`_. This modified behavior is due to the declaration of ``ON UPDATE CURRENT_TIMESTAMP`` in the TimestampField's column definition DDL. Like its parent DateTimeField, the TimestampField's options ``auto_now``, ``auto_now_add``, and ``auto_now_update`` will forcibly overwrite any manually-set model field attribute values when enabled and when their conditions are triggered. The value will be the Django ORM database function `Now() <https://docs.djangoproject.com/en/dev/ref/models/database-functions/#now>`_ rather than a datetime instance since the value will have been generated by the database server and must therefore be retrieved with a separate query. Naturally, when designing a system field instead of a user data field, the need to offload responsibility to the underlying database becomes greater. If the data is for system and metadata purposes, then it increases consistency and data integrity to delegate field value management to the system itself. A timestamp is well-suited to record system and database record metadata such as record insert and update times. Due to the database data type features, it is also ideal when storing a fixed point in time, independent of time zone. Although the creation of the TimestampField was largely motivated by the need for an ORM abstraction for metadata fields, it can also be used just like its parent DateTimeField as long as one understands the data type's different advantages and limitations. Instead of DateTimeField's reliance on ``DATETIME`` and similar data types, the TimestampField uses ``TIMESTAMP`` data type and other data types that do not store time zone information. The data type changes can be seen in the following table: ========== ======================= =========================== database DateTimeField data type TimestampField data type ========== ======================= =========================== MySQL DATETIME TIMESTAMP PostgreSQL TIMESTAMP WITH TIMEZONE TIMESTAMP WITHOUT TIME ZONE SQLite DATETIME DATETIME ========== ======================= =========================== Also note that standard DDL modifiers such as ``DEFAULT CURRENT TIMESTAMP`` and non-standard ones such as MySQL's ``ON UPDATE CURRENT_TIMESTAMP`` are used when the corresponding options on a TimestampField instance are enabled. ****************************** Database Engine Considerations ****************************** When using TimestampField, one must be aware of certain database engine behavior defaults and configurations. An ORM is usually designed to abstract, as much as is practical and prudent, the differences between the underlying databases. In this case, however, the abstraction leaks. Consider the following timestamp column DDL:: TIMESTAMP NOT NULL Note the lack of a ``DEFAULT`` clause. One would expect, upon attempting to insert a ``NULL`` value or failing to provide a value for the column altogether, that some sort of constraint or integrity exception would be raised. Indeed, this behavior adheres to the principle of least astonishment and is the standard behavior of both SQLite and PostgreSQL. Both `SQLite <https://www.sqlite.org/lang_createtable.html>`_ and `PostgreSQL <https://www.postgresql.org/docs/current/static/ddl-default.html>`_ implicitly assign ``DEFAULT NULL`` to column definitions with no explicit ``DEFAULT`` clause. MySQL ===== MySQL requires a specific configuration to achieve the same standard behavior. The following configuration options affect ``TIMESTAMP`` columns: - `strict mode <https://dev.mysql.com/doc/refman/en/sql-mode.html#sql-mode-strict>`_ - `NO_ZERO_DATE <https://dev.mysql.com/doc/refman/en/sql-mode.html#sqlmode_no_zero_date>`_ - `NO_ZERO_IN_DATE <https://dev.mysql.com/doc/refman/en/sql-mode.html#sqlmode_no_zero_in_date>`_ - `explicit_defaults_for_timestamp <https://dev.mysql.com/doc/refman/en/server-system-variables.html#sysvar_explicit_defaults_for_timestamp>`_ At minimum, MySQL requires that both strict mode and ``explicit_defaults_for_timestamp`` are enabled for ``TIMESTAMP`` behavior to conform to standards. If one attempts to omit a value for the ``TIMESTAMP NOT NULL`` column, a "ERROR 1364 (HY000): Field <field_name> doesn't have a default value" is emitted and if one attempts to insert a ``NULL`` value, a "ERROR 1048 (23000): Column <field_name> cannot be null" is emitted. As of version MySQL 5.7, strict mode is enabled by default but ``explicit_defaults_for_timestamp`` is not. MariaDB ======= MariaDB, on the other hand, applies the same configuration parameters in a different way and its logic as it relates to ``TIMESTAMP NOT NULL`` is less clear and, dare I say, erroneous. Assuming identical configuration (strict mode and ``explicit_defaults_for_timestamp`` enabled), MariaDB raises "ERROR 1364 (HY000): Field <field_name> doesn't have a default value" on insert value omission but successfully accepts a ``NULL`` value with no error and stores the results of ``CURRENT_TIMESTAMP()`` in the field instead. In an attempt to bring MariaDB in line with the standard, I also tested ``NO_ZERO_DATE`` and ``NO_ZERO_IN_DATE``. As long as both ``explicit_defaults_for_timestamp`` and ``NO_ZERO_DATE`` or ``NO_ZERO_IN_DATE`` are enabled, it is impossible to create a table containing the ``TIMESTAMP NOT NULL`` column as the ``CREATE TABLE`` statement fails with "ERROR 1067 (42000): Invalid default value for <field_name>". This suggests that not only is the ``DEFAULT`` value validated during DDL statements, but MariaDB is also attempting to implicitly define a zero value ``DEFAULT`` value on the ``TIMESTAMP`` field as the same error is raised when ``DEFAULT '0000-00-00 00:00:00'`` is explicitly defined. This is nonstandard, erroneous behavior and conflicts with that of MySQL. From the `MySQL documentation <https://dev.mysql.com/doc/refman/en/server-system-variables.html#sysvar_explicit_defaults_for_timestamp>`_: ``TIMESTAMP`` columns explicitly declared with the ``NOT NULL`` attribute and without an explicit ``DEFAULT`` attribute are treated as having no default value. From the same documentation page, the following governs ``INSERT`` operations under these conditions: For inserted rows that specify no explicit value for such a column, the result depends on the SQL mode. If strict SQL mode is enabled, an error occurs. If strict SQL mode is not enabled, the column is declared with the implicit default of '0000-00-00 00:00:00' and a warning occurs. This is similar to how MySQL treats other temporal types such as DATETIME. The DDL validation failure may have something to do with these ``INSERT`` rules. It is impossible for MariaDB's ``TIMESTAMP`` fields to behave in a standard way when dealing with ``TIMESTAMP NOT NULL`` columns. I found `this bug report <https://jira.mariadb.org/browse/MDEV-10802>`_ for MariaDB but it appears that the work has ceased and the fix has not been merged into the target release. All tests were performed on MariaDB 10.2 and 10.3. Conclusion ========== I now have a choice to make: do I cause TimestampField to step aside and let the user more directly experience the effects of the underlying database engine's configuration or do I attempt to abstract the behavior differences as much as possible? Given the spirit and goal of this library, I have opted for less abstraction and have removed any additional, artificial normalization of database engine behavior in these field classes. I am certainly open to discussion on this point so please don't hesitate to open communication with me or point out any errors in my testing. Given MariaDB's deviation from standards, this package's unit tests are performed using MySQL and testing on MariaDB is disabled until further notice. As an aside, please note that many inconsistent behaviors between database engines can be mitigated or even eliminated by explicitly defining field keyword arguments such as ``default``, ``null``, etc., causing more explicit DDL SQL to be generated by Django in the resulting migrations and SQL. *********** Development *********** To set up the development environment, a Vagrantfile is included. Install `Vagrant <https://www.vagrantup.com/>`_ and:: vagrant up Once Vagrant has completed provisioning, ``vagrant ssh`` into the box and start the database servers against which to run the test suite:: docker-compose up -d Finally, run the tests with:: make tests The Vagrant machine is provisioned to use the UTC time zone to facilitate tests. If you elect to run tests outside of the Vagrant machine, be aware that certain tests assume identical time, date, and time zone settings between all database engines. SQLite defaults to the host's localtime while the Docker containers use the host's clock and default to the UTC time zone. In this project, I use PEP8 and `Google's Python style guide <https://google.github.io/styleguide/pyguide.html>`_. Pylint doesn't play nicely with some of the styles. A few notes on pylint: * bad-continuation * Ignore most of these. Google style guide allows for a 4-space hanging indent with nothing on first line. * Example: `indentation <https://google.github.io/styleguide/pyguide.html?showone=Indentation#Indentation>`_ ************** Oracle Support ************** The FixedCharField should work on Oracle but the TimestampField will default to DateTimeField database field data types when used with Oracle. I neither implemented functionality for nor tested on Oracle for a few reasons: #. It is too difficult to get an Oracle server instance against which to test. As one can see, I use lightweight Docker containerized services to run the test databases. To use Oracle, one needs to provide the Oracle installation binaries. To get the binaries, one needs to sign in to Oracle's web site for the privilege of downloading over 2.5 gigabytes. Too much unnecessary pain, not enough return. If you use Oracle products, I sympathize and may god have mercy on your soul. * https://github.com/oracle/docker-images/tree/master/OracleDatabase #. Oracle seems to be `rarely used with Django <https://www.djangosites.org/stats/>`_. #. I hate Oracle products and Oracle as an entity. ********* Changelog ********* v1.0 ==== * Automatic values from ``auto_now``, ``auto_now_add``, and ``auto_now_update`` are no longer generated in the application using ``datetime.datetime.now()`` or ``django.utils.timezone.now()``. ``CURRENT_TIMESTAMP`` generation is now performed by the database using the Django database function `django.db.models.functions.Now <https://docs.djangoproject.com/en/dev/ref/models/database-functions/#now>`_. * All fields now cause the ORM to issue explicit ``DEFAULT`` clauses in column DDL statements where previously the ORM always omitted ``DEFAULT`` clauses from column definitions. ``DEFAULT`` clauses will be defined in DDL if Field.has_default() returns True. This behavior naturally includes the generation of ``DEFAULT NULL`` in the column DDL if the field's ``default`` option is set to ``None``. * If no kwargs (options) are passed to TimestampField, no ``DEFAULT`` clause is generated in the column DDL for MySQL. Previously, a ``DEFAULT NULL`` or ``DEFAULT 0`` clause was output in the DDL to disable MySQL's default ``TIMESTAMP`` behavior. Howver, default ``TIMESTAMP`` behavior varies according to certain server system variables and, depending upon configuration, it may be completely valid to omit a ``DEFAULT`` clause altogether. * FixedCharField will now attempt to insert ``NULL`` if no value is defined on the model's field attribute and no explicit field default value has been defined. This behavior is in contrast to Django's standard CharField which always attempts to (incorrectly) store an empty string in such a case.

نیازمندی

مقدار	نام
-	django
xtr	docker-compose;
xtr	mysqlclient;
xtr	psycopg2-binary;
xtr	pylint;
xtr	twine;
xtr	wheel;

نحوه نصب

نصب پکیج whl django-forcedfields-1.0.1:

pip install django-forcedfields-1.0.1.whl

نصب پکیج tar.gz django-forcedfields-1.0.1:

pip install django-forcedfields-1.0.1.tar.gz