overhaul session.binds to support classes fully; fix up tests

[Mike Bayer]

right now session.__binds uses mappers completely. This makes it impossible to feed in abstract classes and also because it links to base_mapper it's not possible to change the bind along a class hierarchy either (like a concrete hierarchy).

propose that __binds stores classes directly, and this can likely be a fallback in addition to what we have now. this is kind of a proof of concept

diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 89d9946..f63adfb 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -636,13 +636,20 @@ class Session(_SessionClassMethods):

         if binds is not None:
             for mapperortable, bind in binds.items():
-                insp = inspect(mapperortable)
-                if insp.is_selectable:
-                    self.bind_table(mapperortable, bind)
-                elif insp.is_mapper:
-                    self.bind_mapper(mapperortable, bind)
+                try:
+                    insp = inspect(mapperortable)
+                except exc.NoInspectionAvailable:
+                    if isinstance(mapperortable, type):
+                        self.bind_cls(mapperortable, bind)
+                    else:
+                        raise exc.ArgumentError("Not acceptable bind target: %s" % mapperortable)
                 else:
-                    assert False
+                    if insp.is_selectable:
+                        self.bind_table(mapperortable, bind)
+                    elif insp.is_mapper:
+                        self.bind_mapper(mapperortable, bind)
+                    else:
+                        assert False


         if not self.autocommit:
@@ -1039,6 +1046,17 @@ class Session(_SessionClassMethods):
         for t in mapper._all_tables:
             self.__binds[t] = bind

+    def bind_class(self, cls, bind):
+        """Bind operations for an unmapped class to a Connectable.
+
+        The behavior here is that a subclass of cls which is mapped
+        will be linked to this bind.
+
+        .. versionadded:: 1.0
+
+        """
+        self.__binds[cls] = bind
+
     def bind_table(self, table, bind):
         """Bind operations on a Table to a Connectable.

@@ -1124,6 +1142,12 @@ class Session(_SessionClassMethods):
                     return self.__binds[c_mapper.base_mapper]
                 elif c_mapper.mapped_table in self.__binds:
                     return self.__binds[c_mapper.mapped_table]
+                else:
+                    for cls in c_mapper.class_.__mro__:
+                        if cls in self.__binds:
+                            bind = self.__binds[cls]
+                            self.bind_mapper(c_mapper, bind)
+                            return bind
             if clause is not None:
                 for t in sql_util.find_tables(clause, include_crud=True):
                     if t in self.__binds:

the tests here also need a rework, with an emphasis on straight unit testing of get_bind(). test_session -> BindTest is really just integration tests.

[Mike Bayer]

here's a better patch, everything passes except for some exception raises:

diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 89d9946..8bb1fc8 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -635,14 +635,8 @@ class Session(_SessionClassMethods):
                 SessionExtension._adapt_listener(self, ext)

         if binds is not None:
-            for mapperortable, bind in binds.items():
-                insp = inspect(mapperortable)
-                if insp.is_selectable:
-                    self.bind_table(mapperortable, bind)
-                elif insp.is_mapper:
-                    self.bind_mapper(mapperortable, bind)
-                else:
-                    assert False
+            for key, bind in binds.items():
+                self._add_bind(key, bind)


         if not self.autocommit:
@@ -1019,40 +1013,45 @@ class Session(_SessionClassMethods):
     # TODO: + crystallize + document resolution order
     #       vis. bind_mapper/bind_table

-    def bind_mapper(self, mapper, bind):
-        """Bind operations for a mapper to a Connectable.
-
-        mapper
-          A mapper instance or mapped class
+    def _add_bind(self, key, bind):
+        try:
+            insp = inspect(key)
+        except sa_exc.NoInspectionAvailable:
+            if not isinstance(key, type):
+                raise exc.ArgumentError(
+                            "Not acceptable bind target: %s" %
+                            key)
+        else:
+            if insp.is_selectable:
+                self.__binds[insp] = bind
+            elif insp.is_mapper:
+                self.__binds[insp.class_] = bind
+                for selectable in insp._all_tables:
+                    self.__binds[selectable] = bind
+            else:
+                raise exc.ArgumentError(
+                            "Not acceptable bind target: %s" %
+                            key)

-        bind
-          Any Connectable: a :class:`.Engine` or :class:`.Connection`.
+    def bind_mapper(self, mapper, bind):
+        """Associate a :class:`.Mapper` with a "bind", e.g. a :class:`.Engine`
+        or :class:`.Connection`.

-        All subsequent operations involving this mapper will use the given
-        `bind`.
+        The given mapper is added to a lookup used by the
+        :meth:`.Session.get_bind` method.

         """
-        if isinstance(mapper, type):
-            mapper = class_mapper(mapper)
-
-        self.__binds[mapper.base_mapper] = bind
-        for t in mapper._all_tables:
-            self.__binds[t] = bind
+        self._add_bind(mapper, bind)

     def bind_table(self, table, bind):
-        """Bind operations on a Table to a Connectable.
-
-        table
-          A :class:`.Table` instance
-
-        bind
-          Any Connectable: a :class:`.Engine` or :class:`.Connection`.
+        """Associate a :class:`.Table` with a "bind", e.g. a :class:`.Engine`
+        or :class:`.Connection`.

-        All subsequent operations involving this :class:`.Table` will use the 
-        given `bind`.
+        The given mapper is added to a lookup used by the
+        :meth:`.Session.get_bind` method.

         """
-        self.__binds[table] = bind
+        self._add_bind(table, bind)

     def get_bind(self, mapper=None, clause=None):
         """Return a "bind" to which this :class:`.Session` is bound.
@@ -1115,15 +1114,23 @@ class Session(_SessionClassMethods):
                     "Connection, and no context was provided to locate "
                     "a binding.")

-        c_mapper = mapper is not None and _class_to_mapper(mapper) or None
+        if mapper is not None:
+            try:
+                mapper = inspect(mapper)
+            except sa_exc.NoInspectionAvailable:
+                if isinstance(mapper, type):
+                    raise exc.UnmappedClassError(mapper)
+                else:
+                    raise

-        # manually bound?
         if self.__binds:
-            if c_mapper:
-                if c_mapper.base_mapper in self.__binds:
-                    return self.__binds[c_mapper.base_mapper]
-                elif c_mapper.mapped_table in self.__binds:
-                    return self.__binds[c_mapper.mapped_table]
+            if mapper:
+                for cls in mapper.class_.__mro__:
+                    if cls in self.__binds:
+                        return self.__binds[cls]
+                if clause is None:
+                    clause = mapper.mapped_table
+
             if clause is not None:
                 for t in sql_util.find_tables(clause, include_crud=True):
                     if t in self.__binds:
@@ -1135,12 +1142,12 @@ class Session(_SessionClassMethods):
         if isinstance(clause, sql.expression.ClauseElement) and clause.bind:
             return clause.bind

-        if c_mapper and c_mapper.mapped_table.bind:
-            return c_mapper.mapped_table.bind
+        if mapper and mapper.mapped_table.bind:
+            return mapper.mapped_table.bind

         context = []
         if mapper is not None:
-            context.append('mapper %s' % c_mapper)
+            context.append('mapper %s' % mapper)
         if clause is not None:
             context.append('SQL expression')

[Mike Bayer]

Issue #3202 was marked as a duplicate of this issue.

[Mike Bayer]

additional test from #3202:

from sqlalchemy import Column, Integer, ForeignKey, create_engine, orm
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class A(Base):
    __tablename__ = 'A'
    id = Column(Integer, primary_key=True)
    type = Column(Integer, nullable=False)
    __mapper_args__ = {'polymorphic_on': type}

class B(A):
    __tablename__ = 'B'
    id = Column(ForeignKey(A.id), primary_key=True)
    __mapper_args__ = {'polymorphic_identity': 1}

engine = create_engine('sqlite://')
binds = {table: engine for table in Base.metadata.sorted_tables}
db = orm.sessionmaker(binds=binds)()

print db.get_bind(A) # Engine(sqlite://)
print db.get_bind(B) # sqlalchemy.exc.UnboundExecutionError: Could not locate a bind configured on mapper Mapper|B|B or this Session

[Mike Bayer]

• Improvements to the mechanism used by :class:.Session to locate "binds" (e.g. engines to use), such engines can be associated with mixin classes, concrete subclasses, as well as a wider variety of table metadata such as joined inheritance tables. fixes #3035

→ <<cset 6de1a878702b>>