infer_discriminator

[samuelcolvin]

Initial Checks

• I have searched Google & GitHub for similar requests and couldn't find anything
• I have read and followed the docs and still think this feature is missing

Description

We should have a config setting which causes Pydantic to try to infer union discriminators.

It's shouldn't try to do anything too clever, it should just look for:

• fields on all members of the union with the same name
• where all fields are literals or enums
• and none of the allowed values overlap

If so, generate a discriminator.

Affected Components

• Compatibility between releases
• Data validation/parsing
• Data serialization - .model_dump() and .model_dump_json()
• JSON Schema
• Dataclasses
• Model Config
• Field Types - adding or changing a particular data type
• Function validation decorator
• Generic Models
• Other Model behaviour - model_construct(), pickling, private attributes, ORM mode
• Plugins and integration with other tools - mypy, FastAPI, python-devtools, Hypothesis, VS Code, PyCharm, etc.

[dmontagu]

If necessary for the use cases you have in mind, I think we could also do this with functional discriminators in the case where there is a required field that is only present in one of the cases. If inferring for literals/enum discriminators is enough then that's probably less effort

[samuelcolvin]

I guess we make the setting:

• False - don't infer, current behaviour
• simple - literals only
• exhaustive - try all the things we can reasonably think of to create a discriminator

Since this method will be on GenerateSchema , any more complex semantics can be implemented by uses.

[NeevCohen]

@samuelcolvin Hey, I'd like to pick this up if it's still available