SQL expression object expected, got object of type <class 'property'> instead

[Simon]

Hi there,

I got a problem about 'sqlalchemy.exc.ArgumentError: SQL expression object expected, got object of type <class 'property'> instead'

My SQLAlchemy version is 1.3.22. I have a database like 

Class Genome:

    id = Column(Integer, primary_key=True)

    created_date = Column(Datetime, nullable=False)

@property

def attributes(self):

     return "something"

If using the query, it reports an error through the elements.py in the sqlAlchemy

def _literal_as(element, text_fallback):
if isinstance(element, Visitable):
return element
elif hasattr(element, "__clause_element__"):
return element.__clause_element__()
elif isinstance(element, util.string_types):
return text_fallback(element)
elif isinstance(element, (util.NoneType, bool)):
return _const_expr(element)
else:
raise exc.ArgumentError(
"SQL expression object expected, got object of type %r "
"instead" % type(element)
)

This exception is not raised if I directly query genome's column name such as created_date or id. 

I am wondering 1) could the column name and property be used interchangeably in some way? Or say how could to query a table's property in the way of querying a table's column? 2) what are some significant differences between table's column name and property?

Thanks.

 

[Simon King]

Can you show the part of *your* code that is triggering the error, and
explain what you are trying to do? Plain python properties aren't
normally very useful when accessed via a class. "Genome.attributes"
returns a property object, not the return value from the function, and
I don't understand what you are trying to do with it.

Thanks,

Simon

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[Simon]

Sorry for that the question is not clear. The question is how can we query a database's property.

Given the above example, if query(Genome.id) or query(Genome.created_date), it works fine. But if I query the property, query(Genome.attributes): it raises the exception. 

Thanks.

Simon

[Simon King]

I'm sorry, I still don't understand - what do you expect
query(Genome.attributes) to do? Can you give an example?

Thanks,

Simon

> To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy/2fbf2d83-6865-4b9b-8db6-cb5f60e0eaffn%40googlegroups.com.

[Simon]

Never mind. This problem is solved by join operations.

 Thanks for your attention.