[Sqlalchemy-tickets] Issue #3863: Bulk save doesn't executemany() when model kwargs are different (zzzeek/sqlalchemy)

[Antoine C. <iss...@bi...>]

New issue 3863: Bulk save doesn't executemany() when model kwargs are different
https://bitbucket.org/zzzeek/sqlalchemy/issues/3863/bulk-save-doesnt-executemany-when-model

Antoine Catton:

Let's consider this dialect in `test.py`:


```
#!python

import sqlalchemy as sa
from sqlalchemy.dialects import registry
from sqlalchemy.dialects.sqlite.pysqlite import SQLiteDialect_pysqlite
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker


class CustomSQLiteDialect(SQLiteDialect_pysqlite):
    def do_executemany(self, cursor, statement, parameters, context=None):
        print("executemany(): statement={s!r}, params={p!r}".format(s=statement, p=parameters))
        super(CustomSQLiteDialect, self).do_executemany(cursor, statement, parameters, context)

    def do_execute(self, cursor, statement, parameters, context=None):
        print("EXECUTE!!(): statement={s!r}, params={p!r}".format(s=statement, p=parameters))
        super(CustomSQLiteDialect, self).do_execute(cursor, statement, parameters, context)
```

And this model:

```
#!python

Base = declarative_base()


class Model(Base):
    __tablename__ = 'model'

    id = sa.Column(sa.Integer, primary_key=True)
    foo = sa.Column(sa.String, default='foo')
    bar = sa.Column(sa.String, default='bar')
```

And run the code:

```
#!python
registry.register("sqlite.custom", "test", "CustomSQLiteDialect")


if __name__ == '__main__':
    engine = sa.create_engine('sqlite+custom:///:memory:')

    Base.metadata.create_all(engine)

    Session = sessionmaker(bind=engine)
    session = Session()


    bulk1 = [Model(foo='a', bar='b'), Model(foo='c', bar='d')]
    print("== Saving first bulk:")
    session.bulk_save_objects(bulk1)


    bulk2 = [Model(foo='a'), Model(bar='b')]
    print("== Saving second bulk:")
    session.bulk_save_objects(bulk2)
```

Here's the output:

```
EXECUTE!!(): statement=u"SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1", params=()
EXECUTE!!(): statement=u"SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1", params=()
EXECUTE!!(): statement=u'PRAGMA table_info("model")', params=()
EXECUTE!!(): statement=u'\nCREATE TABLE model (\n\tid INTEGER NOT NULL, \n\tfoo VARCHAR, \n\tbar VARCHAR, \n\tPRIMARY KEY (id)\n)\n\n', params=()
== Saving first bulk:
executemany(): statement=u'INSERT INTO model (foo, bar) VALUES (?, ?)', params=(('a', 'b'), ('c', 'd'))
== Saving second bulk:
EXECUTE!!(): statement=u'INSERT INTO model (foo, bar) VALUES (?, ?)', params=('a', 'bar')
EXECUTE!!(): statement=u'INSERT INTO model (foo, bar) VALUES (?, ?)', params=('foo', 'b')
```

I don't see a reason why the second bulk should do many `execute()`.