f0b8204072
As discussed at our nova meetings, reorganize the juno specs into three directories: - proposed: things proposed which weren't approved - approved: things we approved but didn't implement - implemented: things approved and implemented The first I suspect is the most controversial. I've done this because I worry about the case where a future developer wants to pick up something dropped by a previous developer, but has trouble finding previous proposed specifications on the topic. Note that the actual proposed specs for Juno are adding in a later commit. Change-Id: Idcf55ca37a83d7098dcb7c2971240c4e8fd23dc8
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=======================================
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Allow StringField to enforce max length
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=======================================
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https://blueprints.launchpad.net/nova/+spec/string-field-max-length
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This blueprint aims to add a max length constraint to the
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`nova.objects.fields.StringField` class.
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Problem description
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===================
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Currently, the nova object framework revolves around the use of field type
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classes that describe the schema of an object. Each object model is simply
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a collection of fields, each of which have a particular type, such as
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IntegerField or StringField.
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In much the same way that a SQL database schema describes the constraints
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that a given column in a table must adhere to -- e.g. the length of characters
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possible in a CHAR field, or a valid DATETIME string -- the nova objects
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should be self-validating.
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Proposed change
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===============
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This specification proposes to change the `coerce` method of the
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`String` class to validate on the number of characters in the
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field's string value.
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The `StringField` concrete field class shall have a new `max_length` kwarg
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added to its constructor that will control the validation. The default
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value will be None, and no `StringField` objects defined in the schemas of
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any of the nova object models shall be changed in this spec.
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Alternatives
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------------
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None (keep things the way they are now)
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Data model impact
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-----------------
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None (the existing models themselves won't be changed in this specification
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at all)
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Roughly, the code the `String` field type class would change from this:
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.. code:: python
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class String(FieldType):
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@staticmethod
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def coerce(obj, attr, value):
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# FIXME(danms): We should really try to avoid the need to do this
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if isinstance(value, (six.string_types, int, long, float,
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datetime.datetime)):
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return unicode(value)
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else:
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raise ValueError(_('A string is required here, not %s') %
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value.__class__.__name__)
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to this:
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.. code:: python
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class String(FieldType):
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def __init__(self, max_length=None):
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"""
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:param max_length: Optional constraint on the number of Unicode
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characters the string value can be.
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"""
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self._max_length = max_length
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@staticmethod
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def coerce(self, obj, attr, value):
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# FIXME(danms): We should really try to avoid the need to do this
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if isinstance(value, (six.string_types, int, long, float,
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datetime.datetime)):
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result = unicode(value)
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else:
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raise ValueError(_('A string is required here, not %s') %
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value.__class__.__name__)
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if self._max_length is not None:
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if len(value) > self._max_length):
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msg = _("String %(result)s is longer than maximum allowed "
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"length of %(max_length)d.")
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msg = msg % dict(result=result,
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max_length=self._max_length)
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raise ValueError(msg)
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return result
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The StringField class would then need to be modified to allow passing the
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max_length parameter along to its type class.
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Work Items
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----------
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N/A
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Assignee(s)
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-----------
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Primary assignee:
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jaypipes
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Dependencies
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============
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None
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Testing
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=======
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Would need new unit tests. No need for any integration test changes.
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Documentation Impact
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====================
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None
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References
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==========
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The server-instance-tagging work will likely be the first work to use
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this functionality, as the tag string has a max length associated with
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it and we need to be very careful about changing existing model fields' string
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length validation code, so a new field like the tag field is an ideal place to
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begin with this implementation.
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http://git.openstack.org/cgit/openstack/nova-specs/tree/specs/juno/tag-instances.rst
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