Allow overriding of attributes when inheriting from classes in wc_kb

[paulflang]

Currently, overriding attributes managed by the ManyToX relationship manager gives for example the following error: ValueError: Attribute "obj_tables.core" of class "Evidence" inherited from "object" must be a subclass of StringAttribute because the attribute is already defined in the superclass.

[jonrkarr]

Please provide an example. It sounds like what you want to do is inconsistent with object oriented programming.

On Sat, Sep 28, 2019, 8:55 PM paulflang notifications@github.com wrote:

Currently overriding attributes managed by the ManyToX relationship manager gives for example the following error: ValueError: Attribute "obj_tables.core" of class "Evidence" inherited from "object" must be a subclass of StringAttribute because the attribute is already defined in the superclass.

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[paulflang]

Doing the following in wc_kb/core.py branch tci_jk:

class Evidence(KnowledgeBaseObject): .... object = obj_tables.StringAttribute()

class TimeCourseEvidence(Evidence): ... object = obj_tables.ManyToOneAttribute('Observable', related_name='time_course_evidences'

Results in the error: "../obj_model/obj_tables/core.py:378: in validate_attribute_inheritance format(name, super_cls.name, attr_name, super_attr.class.name)) E ValueError: Attribute "obj_tables.core" of class "Evidence" inherited from "object" must be a subclass of StringAttribute because the attribute is already defined in the superclass"

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Similarly doing

class Evidence(KnowledgeBaseObject): ... value = obj_tables.FloatAttribute()

class TimeCourseEvidence(Evidence): .... values = obj_tables.obj_math.NumpyArrayAttribute()

Results in: "TypeError: 'values_tce' is an invalid keyword argument for TimeCourseEvidence.init"

[jonrkarr]

We have intentionally not allowed this design pattern because it can introduce confusion for users. Generally, this design pattern should be avoided in all programming. This is codified by the Open–closed principle, one of the five major principles of object-oriented programming. This design pattern would also be inconsistent with the Principle of least astonishment.

A different design should be used that does not require changing the types of attributes in subclasses. One possibility is to use an abstract superclass rather than a concrete superclass, although some would probably argue that this design would still violate the above principles. A better design would be to (a) avoid inheritance or (b) only add attributes in subclasses.