使用多个表中的数据的唯一约束（SQL / SQLAlchemy）

Question

A top class called Parametric is used to create objects which can have parameters associated with them:

class Parametric(object):
 def __init__(self, name):
  self.name = name
  self.pars = []

class Foo(Parametric):
 def __init__(self, name, prop):
  self.prop = prop
  Parametric.__init__(self, name)

class Bar(Parametric):
 def __init__(self, name, prop):
  self.prop = prop
  Parametric.__init__(self, name)

I use SQLAlchemy for my ORM engine.

I want to impose a UNIQUE constraint that ensures that the combination ( name , prop ) are unique for a given class (eg only one instance of Foo can be called "my_foo" and have a prop value of, say "my_prop" ), but I don't see how to reference the name column from Parametric in the Foo table UNIQUECONSTRAINT section.

Is this uniqueness something which can be imposed via FOREIGN KEY directives?

Answer 1

You could do this using single table inheritance . However if your two columns are in different tables, you can't do exactly what you're trying to do (it is not possible to do a unique constraint across tables).

If single table inheritance is not an option, you probably want to either (1) enforce uniqueness in python, or (2) abandon sqlalchemy inheritance, and just use a foreign key to link Foo and Bar to Parametric. You could foreign key to name , and THEN do a unique constraint on name and prop .

Answer 2

如果有 2 个不同的表，您可以在表单验证中检查它是否重复。