Support more json schema `$ref` patterns

[Kilo59]

Feature Request

I would like to be able to generate more types of references than can be created via a simple ref_prefix. For example, referencing a schema that resides in another file.

{ "$ref": "/schemas/Foo.json#/}

https://json-schema.org/understanding-json-schema/structuring.html#reuse
https://docs.opis.io/json-schema/1.x/pointers.html

Example

import json
from pydantic import BaseModel
from pydantic.schema import schema

class Foo(BaseModel):
    a: int

class Model(BaseModel):
    a: Foo

# Default location for OpenAPI
model_schema = Model.schema(ref_template='/schemas/{name}.json#/')
print(json.dumps(model_schema , indent=2))

{
  "Model": {
    "title": "Model",
    "type": "object",
    "properties": {
      "a": {
        "$ref": "/schemas/Foo.json#/"
      }
    },
    "required": ["a"]
  }
}

I believe python's string.Template could be a good way to implement this (which I have attempted).
There are still some details that need to be worked out.

Pull request

[samuelcolvin]

Sorry for the slow reply and thanks for the feature request and PR.

I haven't personally used $ref so I'm personally kind of neutral on the feature.

To accept it I guess I would hope for some other interest here via some 👍s.

Regarding how it's implemented, I don't think it needs string.Template. .format() should work find, e.g. something like

ref_template = ref_template or '#/definitions/{model}'
m_schema = {'$ref': ref_template.format(model=model_name)}

I guess to be clean, if this is accepted, we should depreciate ref_prefix in v2 and replaced it with ref_template

[Kilo59]

@samuelcolvin just updated the PR to use .format
Should I add a Deprecation warning?