关于python：如何使用SQLAlchemy Core在子查询中插入多个值？

How to insert multiple values with subquery using SQLAlchemy Core?

使用SQLAlchemy Core(不是ORM)，我正在尝试使用值中的子查询来插入多行。对于MySQL，实际的SQL如下所示：

1
2
3

INSERT INTO widgets (name, type) VALUES
('Melon', (SELECT type FROM widgetTypes WHERE type='Squidgy')),
('Durian', (SELECT type FROM widgetTypes WHERE type='Spiky'))

但是在insert()子句上使用values()方法时，我似乎只能使用子查询，该子句一次只能插入一个。我想一次将多个值作为绑定参数的列表传递给Connection \\的execute()方法，从而一次插入多个值，但这似乎不受支持。

是否可以在一次调用execute()的情况下做我想做的事情？

这是一个自成一体的示范。请注意，这使用了sqlite引擎，该引擎不支持与MySQL相同的方式进行多次插入，但是SQLAlchemy代码仍然以与真实MySQL应用程序相同的方式失败。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54

from sqlalchemy import *

if __name__ =="__main__":
# Construct database
metadata = MetaData()
widgetTypes = Table('widgetTypes', metadata,
Column('id', INTEGER(), primary_key=True),
Column('type', VARCHAR(), nullable=False),
)
widgets = Table('widgets', metadata,
Column('id', INTEGER(), primary_key=True),
Column('name', VARCHAR(), nullable=False),
Column('type', INTEGER(), nullable=False),
ForeignKeyConstraint(['type'], ['widgetTypes.id']),
)
engine = create_engine("sqlite://")
metadata.create_all(engine)

# Connect and populate db for testing
conn = engine.connect()
conn.execute(widgetTypes.insert(), [
{'type': 'Spiky'},
{'type': 'Squidgy'},
])

# Some select queries for later use.
select_squidgy_id = select([widgetTypes.c.id]).where(
widgetTypes.c['type']=='Squidgy'
).limit(1)
select_spiky_id = select([widgetTypes.c.id]).where(
widgetTypes.c['type']=='Squidgy'
).limit(1)

# One at a time works via values()
conn.execute(widgets.insert().values(
{'name': 'Tomato', 'type': select_squidgy_id},
))

# And multiple values work if we avoid subqueries
conn.execute(
widgets.insert(),
{'name': 'Melon', 'type': 2},
{'name': 'Durian', 'type': 1},
)

# Check above inserts did actually work
print conn.execute(widgets.select()).fetchall()

# But attempting to insert many at once with subqueries does not work.
conn.execute(
widgets.insert(),
{'name': 'Raspberry', 'type': select_squidgy_id},
{'name': 'Lychee', 'type': select_spiky_id},
)

运行它，它死于最后一个execute()调用，其内容为：

sqlalchemy.exc.InterfaceError: (InterfaceError) Error binding
parameter 1 - probably unsupported type. u'INSERT INTO widgets (name,
type) VALUES (?, ?)' (('Raspberry', ), ('Lychee',
))