Re: [Sqlalchemy-tickets] [sqlalchemy] #2828: emit warning when Column is assigned directly to multiple names (was: column_property hides original column)

[sqlalchemy <mi...@zz...>]

#2828: emit warning when Column is assigned directly to multiple names
------------------------------+-------------------------------
      Reporter:  jerryji      |      Owner:  zzzeek
          Type:  defect       |     Status:  new
      Priority:  medium       |  Milestone:  0.8.xx
     Component:  declarative  |   Severity:  major - 1-3 hours
    Resolution:               |   Keywords:  column_property
Progress State:  needs tests  |
------------------------------+-------------------------------
Changes (by zzzeek):

 * milestone:   => 0.8.xx
 * component:  orm => declarative
 * severity:  no triage selected yet => major - 1-3 hours
 * status_field:  awaiting triage => needs tests


Comment:

 there's no bug here, the declaration of `name = Column` is equivalent of
 `name_alias = column_property(Column)`, and an explicit column property
 trumps the plain column as you might be passing extra mapping options
 along.   We can emit a warning for when this occurs, this patch is a
 start, needs some cleanup and tests:

 {{{
 #!python
 diff --git a/lib/sqlalchemy/ext/declarative/base.py
 b/lib/sqlalchemy/ext/declarative/base.py
 index 820c087..73723bc 100644
 --- a/lib/sqlalchemy/ext/declarative/base.py
 +++ b/lib/sqlalchemy/ext/declarative/base.py
 @@ -14,7 +14,7 @@ from ... import util, exc
  from ...sql import expression
  from ... import event
  from . import clsregistry
 -
 +import collections

  def _declared_mapping_info(cls):
      # deferred mapping
 @@ -173,15 +173,19 @@ def _as_declarative(cls, classname, dict_):

      # extract columns from the class dict
      declared_columns = set()
 +    col_to_prop = collections.defaultdict(dict)
      for key, c in list(our_stuff.items()):
          if isinstance(c, (ColumnProperty, CompositeProperty)):
              for col in c.columns:
                  if isinstance(col, Column) and \
                      col.table is None:
                      _undefer_column_name(key, col)
 +                    if isinstance(c, ColumnProperty):
 +                        col_to_prop[col][key] = c
                      declared_columns.add(col)
          elif isinstance(c, Column):
              _undefer_column_name(key, c)
 +            col_to_prop[c][key] = c
              declared_columns.add(c)
              # if the column is the same name as the key,
              # remove it from the explicit properties dict.
 @@ -190,6 +194,10 @@ def _as_declarative(cls, classname, dict_):
              # in multi-column ColumnProperties.
              if key == c.key:
                  del our_stuff[key]
 +    for col, entry in col_to_prop.items():
 +        if len(entry) > 1:
 +            util.warn("Column object named directly multiple times, "
 +                "only one will be used: %s" % (", ".join(entry)))
      declared_columns = sorted(
          declared_columns, key=lambda c: c._creation_order)
      table = None
 diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
 index 4336c19..f828180 100644
 --- a/lib/sqlalchemy/orm/mapper.py
 +++ b/lib/sqlalchemy/orm/mapper.py
 @@ -1218,7 +1218,6 @@ class Mapper(_InspectionAttr):
              self._log("Identified primary key columns: %s", primary_key)

      def _configure_properties(self):
 -
          # Column and other ClauseElement objects which are mapped
          self.columns = self.c = util.OrderedProperties()

 }}}

 this also should probably try to detect if a straight Column is specified
 multiple times.

 in this use case you want to be using
 [http://docs.sqlalchemy.org/en/rel_0_8/orm/mapper_config.html?highlight=synonym#sqlalchemy.orm.synonym
 synonym] in order to produce a straight "alias" of a name.

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2828#comment:1>
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