[Sqlalchemy-tickets] Issue #4374: Feature Request: Issue warning when mapper discovers a member that is a function. (zzzeek/sqlalchemy)

[Dave S. <iss...@bi...>]

New issue 4374: Feature Request: Issue warning when mapper discovers a member that is a function.
https://bitbucket.org/zzzeek/sqlalchemy/issues/4374/feature-request-issue-warning-when-mapper

Dave Scotese:

My code required a capital C in "Column" but I used a lower-case c, and this resulted in my database table NOT containing the column I defined.  Ultimately, this appeared as "sqlalchemy.exc.NoForeignKeysError" because the column that didn't get put into my table is the foreign key.  The code that reference the missing column may have created a problem that wasn't reported in the Werkzeug Traceback, or it may have been reported in a way that I didn't see.  Here is the end of it:

    sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship Resource.locale - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

I finally examined the database and discovered there was no column and traced that problem back to the bad letter case.  I explored the two identifiers (Column and column):

    >>> import sqlalchemy
    >>> from sqlalchemy import create_engine
    >>> e = create_engine('sqlite:///:memory:', echo=True)
    >>> from sqlalchemy.ext.declarative import declarative_base
    >>> Base = declarative_base()
    >>>  from sqlalchemy import Column, Integer, String
      File "<stdin>", line 1
        from sqlalchemy import Column, Integer, String
        ^
    IndentationError: unexpected indent
    >>> from sqlalchemy import Column, Integer, String
    >>> from sqlalchemy import column
    >>> column(Integer, primary_key=True)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: column() got an unexpected keyword argument 'primary_key'
    >>> column(Integer)
    <sqlalchemy.sql.elements.ColumnClause at 0x7f8acaeafac8; <class 'sqlalchemy.sql.sqltypes.Integer'>>
    >>> column
    <function column at 0x7f8acafccbf8>
    >>> Column
    <class 'sqlalchemy.sql.schema.Column'>

So it seems that when SQLAlchemy examines a mapped class, it can find a member of the class that is a function ("column") or an instance of a class ("Column"), and it is silent in both cases.  It may be useful to declare a member of a mapped class to be a function, but it seems it would be useful for SQLAlchemy to issue a warning when that happens.