ColumnPoperty.merge() w/ load=False calls expire_attributes on a deferred, forcing it to load on unexpire

[Mike Bayer]

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    d1 = deferred(Column(String))
    d2 = Column(String)

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

a1 = A(d1='d1', d2='d2')

s = Session(e)
s.add(a1)
s.commit()
s.close()

a1 = s.query(A).first()

s.expire(a1, ['d2'])
s.close()

a1 = s.merge(a1, load=False)
print "---------------"
# emits load for d1 also
print a1.d2

this is not the fix because it does not take the strategy itself or load_options into account, but this is the idea:

diff --git a/lib/sqlalchemy/orm/properties.py b/lib/sqlalchemy/orm/properties.py
index 55e0298..2bc9626 100644
--- a/lib/sqlalchemy/orm/properties.py
+++ b/lib/sqlalchemy/orm/properties.py
@@ -217,7 +217,7 @@ class ColumnProperty(StrategizedProperty):
             else:
                 impl = dest_state.get_impl(self.key)
                 impl.set(dest_state, dest_dict, value, None)
-        elif dest_state.has_identity and self.key not in dest_dict:
+        elif dest_state.has_identity and self.key not in dest_dict and not self.deferred:
             dest_state._expire_attributes(dest_dict, [self.key])

     class Comparator(util.MemoizedSlots, PropComparator):

[Mike Bayer]

here's the final patch w/o tests, which also introduces that we copy the callables_ over from the loaded state:

diff --git a/lib/sqlalchemy/orm/properties.py b/lib/sqlalchemy/orm/properties.py
index 55e0298..33a3dec 100644
--- a/lib/sqlalchemy/orm/properties.py
+++ b/lib/sqlalchemy/orm/properties.py
@@ -218,7 +218,8 @@ class ColumnProperty(StrategizedProperty):
                 impl = dest_state.get_impl(self.key)
                 impl.set(dest_state, dest_dict, value, None)
         elif dest_state.has_identity and self.key not in dest_dict:
-            dest_state._expire_attributes(dest_dict, [self.key])
+            dest_state._expire_attributes(
+                dest_dict, [self.key], no_loader=True)

     class Comparator(util.MemoizedSlots, PropComparator):
         """Produce boolean, comparison, and other operators for
diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 4619027..948678b 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -1784,6 +1784,13 @@ class Session(_SessionClassMethods):
             merged_state.load_path = state.load_path
             merged_state.load_options = state.load_options

+            # since we are copying load_options, we need to copy
+            # the callables_ that would have been generated by those
+            # load_options.
+            # assumes that the callables we put in state.callables_
+            # are not instance-specific (which they should not be)
+            merged_state._copy_callables(state)
+
             for prop in mapper.iterate_properties:
                 prop.merge(self, state, state_dict,
                            merged_state, merged_dict,
diff --git a/lib/sqlalchemy/orm/state.py b/lib/sqlalchemy/orm/state.py
index 6034e74..dc55b99 100644
--- a/lib/sqlalchemy/orm/state.py
+++ b/lib/sqlalchemy/orm/state.py
@@ -391,6 +391,10 @@ class InstanceState(interfaces.InspectionAttr):
         if self.callables:
             self.callables.pop(key, None)

+    def _copy_callables(self, from_):
+        if 'callables' in from_.__dict__:
+            self.callables = dict(from_.callables)
+
     @classmethod
     def _instance_level_callable_processor(cls, manager, fn, key):
         impl = manager[key].impl
@@ -443,7 +447,7 @@ class InstanceState(interfaces.InspectionAttr):

         self.manager.dispatch.expire(self, None)

-    def _expire_attributes(self, dict_, attribute_names):
+    def _expire_attributes(self, dict_, attribute_names, no_loader=False):
         pending = self.__dict__.get('_pending_mutations', None)

         callables = self.callables
@@ -451,6 +455,12 @@ class InstanceState(interfaces.InspectionAttr):
         for key in attribute_names:
             impl = self.manager[key].impl
             if impl.accepts_scalar_loader:
+                if no_loader and (
+                    impl.callable_ or
+                    key in callables
+                ):
+                    continue
+
                 self.expired_attributes.add(key)
                 if callables and key in callables:
                     del callables[key]

tests are:

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    d1 = deferred(Column(String))
    d2 = Column(String)

# ...
s.expire(a1, ['d2'])
s.close()

a1 = s.merge(a1, load=False)
print "---------------"
# should not emit load for d1 also
print a1.d2


print "---------------"
# loads correctly
print a1.d1

and then for the local callable:

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    d1 = Column(String)
    d2 = Column(String)

# ...

# defer at query level instead of mapping level
a1 = s.query(A).options(defer(A.d1)).first()

s.expire(a1, ['d2'])
#s.close()

s2 = Session(e)
print "^^^"
a1 = s2.merge(a1, load=False)
print "---------------"
# should not emit load for d1 also
print a1.d2


print "---------------"
# loads correctly
print a1.d1

[diana clarke]

A pull request with the above patch, plus some tests:

https://github.com/zzzeek/sqlalchemy/pull/256

[Mike Bayer]

• don't load deferred columns on unexpire for merge with load=False, fixes #3488

Change-Id: Ic9577b800e4a4e2465ec7f3a2e95bd231f5337ee Co-Authored-By: Mike Bayer [e-mail]

→ <<cset bef15a950ec4>>

[Mike Bayer]

Merge "- don't load deferred columns on unexpire for merge with load=False, fixes #3488"

→ <<cset 829bd30834cc>>