我正在使用SQLAlchemy 1.3.4和PostgreSQL 11.3。
我有以下(简化的)表定义:
class MyModel(Base):
__tablename__ = 'mymodel'
id = Column(Integer, primary_key=True)
col1 = Column(Unicode, nullable=False)
col2 = Column(Unicode, nullable=False)
col3 = Column(Unicode, nullable=False)
col4 = Column(Boolean)
created_at = Column(DateTime(timezone=True), nullable=False)
updated_at = Column(DateTime(timezone=True), nullable=False)
__table_args__ = (
Index('uq_mymodel_col1_col2_col3_col4',
col1, col2, col3, col4,
unique=True, postgresql_where=col4.isnot(None)),
Index('uq_mymodel_col1_col2_col3',
col1, col2, col3,
unique=True, postgresql_where=col4.is_(None)),
)
(我必须创建2个唯一索引而不是UniqueConstraint
,因为UniqueConstraint
允许具有相同(col1, col2, col3)
的多行是col4
为空,我这样做不需要)
我正在尝试执行以下查询:
INSERT INTO mymodel (col1, col2, col3, col4, created_at, updated_at)
VALUES (%(col1)s, %(col2)s, %(col3)s, %(col4)s, %(created_at)s, %(updated_at)s)
ON CONFLICT DO UPDATE SET updated_at = %(param_1)s
RETURNING mymodel.id
我不知道如何正确使用SQLAlchemy的on_conflict_do_update()
。 :-/
这是我尝试过的:
values = {…}
stmt = insert(MyModel.__table__).values(**values)
stmt = stmt.returning(MyModel.__table__.c.id)
stmt = stmt.on_conflict_do_update(set_={'updated_at': values['updated_at']})
result = dbsession.connection().execute(stmt)
但是SQLAlchemy抱怨:Either constraint or index_elements, but not both, must be specified unless DO NOTHING
我不清楚如何使用constraint
或index_elements
。
我尝试了几件事,无济于事。例如:
values = {…}
stmt = insert(MyModel.__table__).values(**values)
stmt = stmt.returning(MyModel.__table__.c.id)
stmt = stmt.on_conflict_do_update(constraint='uq_mymodel_col1_col2_col3_col4'
set_={'updated_at': values['updated_at']})
result = dbsession.connection().execute(stmt)
但是,这也不起作用:constraint "uq_mymodel_col1_col2_col3_col4" for table "mymodel" does not exist
。但是它确实存在。 (我什至从pgsql复制粘贴,以确保我没有打错字)
无论如何,我有两个可能引发冲突的独特约束,但是on_conflict_do_update()
似乎只有一个约束。所以我也尝试同时指定两者:
values = {…}
stmt = insert(MyModel.__table__).values(**values)
stmt = stmt.returning(MyModel.__table__.c.id)
stmt = stmt.on_conflict_do_update(constraint='uq_mymodel_col1_col2_col3_col4'
set_={'updated_at': values['updated_at']})
stmt = stmt.on_conflict_do_update(constraint='uq_mymodel_col1_col2_col3'
set_={'updated_at': values['updated_at']})
result = dbsession.connection().execute(stmt)
但是我遇到了同样的错误,即uq_mymodel_col1_col2_col3_col4
不存在。
在这一点上,我只是无法弄清楚如何执行上述查询,并且会非常感谢您的帮助。
答案 0 :(得分:0)
好吧,我想我明白了。因此问题根本不是来自SQLAlchemy,实际上我是在滥用PostgreSQL。
首先,我上面粘贴的SQL查询不起作用,因为PostgreSQL与SQLAlchemy一样,需要指定索引列或约束名称。
当我指定我的约束之一时,PostgreSQL给了我与SQLAlchemy相同的错误。那是因为我的约束实际上不是约束,而是唯一索引。看来它确实必须是唯一的约束,而不是唯一的索引。 (即使该索引与唯一约束具有相同的效果)
所以我将模型重写如下:
# Feel free to use the following code under the MIT license
class NullableBoolean(TypeDecorator):
"""A three-states boolean, which allows working with UNIQUE constraints
In PostgreSQL, when making a composite UNIQUE constraint where one of the
columns is a nullable boolean, then null values for that column are counted
as always different.
So if you have:
class MyModel(Base):
__tablename__ = 'mymodel'
id = Column(Integer, primary_key=True)
col1 = Column(Unicode, nullable=False)
col2 = Column(Unicode, nullable=False)
col3 = Column(Boolean)
__table_args__ = (
UniqueConstraint(col1, col2, col3,
name='uq_mymodel_col1_col2_col3'),
}
Then you could INSERT multiple records which have the same (col1, col2)
when col3 is None.
If you want None to be considered a "proper" value that triggers the
unicity constraint, then use this type instead of a nullable Boolean.
"""
impl = Enum
def __init__(self, **kwargs):
kwargs['name'] = 'nullable_boolean_enum'
super().__init__('true', 'false', 'unknown', **kwargs)
def process_bind_param(self, value, dialect):
"""Convert the Python values into the SQL ones"""
return {
True: 'true',
False: 'false',
None: 'unknown',
}[value]
def process_result_value(self, value, dialect):
"""Convert the SQL values into the Python ones"""
return {
'true': True,
'false': False,
'unknown': None,
}[value]
class MyModel(Base):
__tablename__ = 'mymodel'
id = Column(Integer, primary_key=True)
col1 = Column(Unicode, nullable=False)
col2 = Column(Unicode, nullable=False)
col3 = Column(Unicode, nullable=False)
col4 = Column(Boolean)
created_at = Column(DateTime(timezone=True), nullable=False)
updated_at = Column(DateTime(timezone=True), nullable=False)
__table_args__ = (
UniqueConstraint(col1, col2, col3, col4,
name='uq_mymodel_col1_col2_col3_col4')
)
现在它似乎按预期运行。
希望对以后的人有所帮助。如果有人有更好的主意,我很感兴趣。 :)