python - sqlalchemy 不是 NULL 选择

Question

如何像在 SQL 中一样添加过滤器以从特定列中选择不为 NULL 的值？

SELECT * 
FROM table 
WHERE YourColumn IS NOT NULL;

我怎样才能对 SQLAlchemy 过滤器做同样的事情？

select = select(table).select_from(table).where(all_filters) 

Answer 1

column_obj != None 将产生 IS NOT NULL constraint :

In a column context, produces the clause a != b. If the target is None, produces a IS NOT NULL.

或使用 is_not() ^*:

Implement the IS NOT operator.

Normally, IS NOT is generated automatically when comparing to a value of None, which resolves to NULL. However, explicit usage of IS NOT may be desirable if comparing to boolean values on certain platforms.

演示:

>>> from sqlalchemy.sql import column
>>> column('YourColumn') != None
<sqlalchemy.sql.elements.BinaryExpression object at 0x10f81aa90>
>>> print(column('YourColumn') != None)
"YourColumn" IS NOT NULL
>>> column('YourColumn').is_not(None)
<sqlalchemy.sql.elements.BinaryExpression object at 0x11081edf0>
>>> print(column('YourColumn').is_not(None))
"YourColumn" IS NOT NULL

你不能在这里使用 is not None，因为 is not object identity inequality test不能像 != 那样被重载；你只会得到 True 而不是 ColumnClause 实例与 None 单例不是同一个对象:

>>> column('YourColumn') is not None
True

---

^*) 该方法以前被命名为 isnot()，并在 SQLAlchemy 1.4 中重命名。旧名称仍可用于向后兼容。