How to identify that an InstrumentedAttribute or its ColumnProperty are read-only?

[Peter Bunyan]

Much like FormAlchemy, I am trying to update my model from a post in a generic manner. I'd like to find out if an Attribute(InstrumentedAttribute) or its associated ColumnProperty is read-only. (please excuse ridiculous example)

class Foo(Base):    

    id = Column(Integer, primary_key=True)

    name = Column(String)    

    title = column_property(

        select([func.UPPER(name)]).\

        where(id==id)

    )

Although setting 'title' will not cause an insert or update in the db transaction, as it is a column_property, it will be settable. I'd like to not set the attribute by using class_mapper(Foo).iterate_properties and being able to determine that it was read_only. I do not ask lightly. I've read extensively and looked through the source code and come up blank. I also acknowledge that I wrote the model so I know it's read only - but I'd rather be lazy and get my update to do the work - after all, that is why I'm using such an excellent ORM.

 

[Michael Bayer]

the column_property has a .columns collection, of which it is usually just columns[0].   If columns[0] is present in the mapped table, the ORM will write to it; otherwise not.

So :

mapper = class_mapper(Foo)

table = mapper.local_table

property = Foo.name.property

expression = property.columns[0]

is_a_regular_mapped_column = table.c.contains_column(expression)

 

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[Peter Bunyan]

Thank you so much. Wonderful!