MongoAlchemy：两个不同DocumentField之一

Question

Using MongoAlchemy , is it possible to have a DocumentField that can be one of two types? Eg:

class A(Document):
    foo = StringField()

class B(Document):
    bar = StringField()

class C(Document):
    child = DocumentField(A or B)

I thought of a few options that might work:

• Give A and B a common parent and then do child = DocumentField(CommonParent) .
• Write a custom Field that overrides DocumentField , but changes the validator to search through a list of types, instead of one.
• Just use an AnythingField . Kinda defeats the point.

But wondered if it was already done?

Answer 1

There was a branch that I never merged (although I did use it for a while) where I implemented polymorphic types:

https://github.com/jeffjenkins/MongoAlchemy/tree/poly-queries

If you're willing to do a bit of bug fixing that's a pretty good option.

Otherwise the easiest thing to do is implement a custom field. I suspect it might be easier to create a regular field that took a list of DocumentField s as inputs and which could distinguish than to mess with DocumentField (which is sort of what the polymorphism branch does, but more complexly).