[Sqlalchemy-tickets] Issue #4178: ORM reconstructor does not trigger when decorating an __init__ method (zzzeek/sqlalchemy)

[Joël P. <iss...@bi...>]

New issue 4178: ORM reconstructor does not trigger when decorating an __init__ method
https://bitbucket.org/zzzeek/sqlalchemy/issues/4178/orm-reconstructor-does-not-trigger-when

Joël Perras:

As mentioned in the [documentation](http://docs.sqlalchemy.org/en/latest/orm/constructors.html?highlight=reconstructor#constructors-and-object-initialization):

> Any method may be tagged as the orm.reconstructor(), even the `__init__` method itself. 

This, however, does not appear to be the case.

I've provided a simple test case based on existing reconstructor tests in `test/orm/test_mapper.py`, shown here as a diff against the current master branch (`399988aaed401ea6fc69aa580b9b71c236a30f16`).

```
#!diff

diff --git a/test/orm/test_mapper.py b/test/orm/test_mapper.py
index 42d114f6f..5f5ed11b9 100644
--- a/test/orm/test_mapper.py
+++ b/test/orm/test_mapper.py
@@ -1652,6 +1652,25 @@ class MapperTest(_fixtures.FixtureTest, AssertsCompiledSQL):
         create_session().query(User).first()
         eq_(recon, ['go'])

+    def test_reconstructor_init(self):
+
+        users = self.tables.users
+
+        recon = []
+
+        class User(object):
+
+            @reconstructor
+            def __init__(self):
+                recon.append('go')
+
+        mapper(User, users)
+
+        User()
+        eq_(recon, [])
+        create_session().query(User).first()
+        eq_(recon, ['go'])
+
```

I attempted to trace down why this was occurring in `orm.mapper.Mapper._configure_class_instrumentation`, but some of the indirection with regards to load events is more opaque to my limited understanding of how the mapper works than I'd like.

This is clearly not a major bug, since the workaround is relatively simple, but wanted to flag it.