Python 如何在 SQLAlchemy 中插入 NULL 值？
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How to insert NULL value in SQLAlchemy?
提问by bodacydo
I've a Tablewith the following column:
我有一个Table以下列：
Column('type', String(128))
How do I set this column to NULL when inserting a new row in database?
在数据库中插入新行时，如何将此列设置为 NULL？
I tried doing this:
我尝试这样做：
self.type = NULL;
There is no NULLtype in Python so I don't know how to do it.
NULLPython 中没有类型，所以我不知道该怎么做。
采纳答案by Hayk Davtyan
Instead of trying
而不是尝试
self.type = NULL
try as Yaroslav Admin suggested
按照Yaroslav 管理员的建议尝试
self.type = None
As Python's equivalent for NULL is None.
因为 Python 的 NULL 等价物是 None。
回答by omeanwell
I know this is an old thread but this worked for me
我知道这是一个旧线程，但这对我有用
self.type = sqlalchemy.sql.null()
回答by Ilja Everil?
As the other answers have pointed out, an explicit NULL can be inserted by passing None, or in case of SQLAlchemy a null()construct, as the value. In fact PEP-249 "DB-API v2.0" clearly states this in "Type Objects and Constructors":
正如其他答案所指出的那样，可以通过传递None或在 SQLAlchemynull()构造的情况下作为值插入显式 NULL 。事实上，PEP-249 "DB-API v2.0" 在"Type Objects and Constructors" 中清楚地说明了这一点：
SQL NULL values are represented by the Python
Nonesingleton on input and output.
SQL NULL 值由
None输入和输出的 Python单例表示。
As a third option one can simply omit the column, if it is nullable:
作为第三种选择，如果列可以为空，则可以简单地省略该列：
t = Table('t', metadata,
Column('a', Integer),
Column('b', Integer))
stmt = t.insert().values(a=1)
engine.execute(stmt)
would effectively insert a new row (1, NULL)in the table t, because a value was not provided for column b. The same applies for mapped classes, which I suppose the original question is actually using (because of the self):
将有效地(1, NULL)在表中插入一个新行t，因为没有为列提供值b。这同样适用于映射类，我认为原始问题实际上正在使用（因为self）：
class T(Base):
__tablename__ = 't'
id = Column(Integer, primary_key=True)
a = Column(Integer)
b = Column(Integer)
session.add(T(a=1))
session.commit()
again effectively results in (default, 1, NULL)being inserted.
再次有效地导致(default, 1, NULL)被插入。
