Swagger-codegen: [PYTHON] Cross-references in definitions leads to circular reference in api

[dtrieschnigg]

Description

When generating a python client api from a swagger specification containing a cross reference, i.e. type A references type B and type B references type A - the resulting python client cannot be used.

Swagger-codegen version

2.3.1

Swagger declaration file content or url

{
    "swagger": "2.0",
    "paths": {},
    "definitions": {
        "MyType1": {
            "properties": {
                "friend": {
                    "$ref": "#/definitions/MyType2"
                }
            }
        },
        "MyType2": {
            "properties": {
                "friend": {
                    "$ref": "#/definitions/MyType1"
                }
            }
        }
    }
}

Command line used for generation

java -jar swagger-codegen-cli.jar generate -i python-swagger-bug.json -l python -o python-bug

Steps to reproduce

java -jar swagger-codegen-cli.jar generate -i python-swagger-bug.json -l python -o python-bug
cd python-bug
python
import swagger_client

gives an ImportError:

ImportError: cannot import name 'MyType1'

Related issues/PRs

Probably related to the javascript issue with circular references
https://github.com/swagger-api/swagger-codegen/issues/8037

Suggest a fix/enhancement

The MyType1 python file refers to MyType2 which in turn refers to MyType1 (which hasn't been initialized). Removing the import in MyType2 to MyType1 fixes the problem.
I suppose the code generator should keep track of the order of the imports in the dependencies and prevent the circular imports.

[piedenis]

Same for me. I define a tree structure with unknown depth, using a circular reference (yaml file):

  ActivityExecution:
    type: "object"
    properties:
      childActivities:
        type: "array"
        items:
          $ref: "#/definitions/ActivityExecution"
   ....

This is supposed to be a valid OpenAPI 2.0. The generated server code (Python-Flask ) contains the following erroneous file:

# swagger_server/models/activity_execution.py
# ...
from swagger_server.models.activity_execution import ActivityExecution  # noqa: F401,E501
# ...
class ActivityExecution(Model):
# ...
    def __init__(self, child_activities: List[ActivityExecution]=None):  # noqa: E501
# ... 

The import fails because the file tries to import itself, while class ActivityExecution class is not yet defined . Anyway, this is doomed to failure because the type hints in the __init__ method refers to ActivityExecution, which is not yet defined (it is _being_ defined actually). I think that you need a "forward reference", as explained here.

[dtrieschnigg]

The import fails because the file tries to import itself, while class ActivityExecution class is not yet defined . Anyway, this is doomed to failure because the type hints in the init method refers to ActivityExecution, which is not yet defined (it is _being_ defined actually). I think that you need a "forward reference", as explained here.

Alternatively, a single import statement could be used at the top:
import swagger_server.models.activity_execution
and where ActivityExecution is used it should become
def __init__(self, child_activities: List[swagger_server.models.activity_executionActivityExecution]=None): # noqa: E501
Would this work?

[piedenis]

@dtrieschnigg: Good idea but it won't :(. I've tried also other flavors of import but these fail also. I think that there is anyway a design problem _in Python_ trying to refer to a class that is not yet defined; forward reference technique is definitely required.

[dtrieschnigg]

@piedenis in your case wouldn't this already work?

from typing import List

# no imports whatsoever

class ActivityExecution():
    def __init__(self, children: List['ActivityExecution']):
        pass

[piedenis]

@dtrieschnigg: Yes. But what you put is just the first step to do in the process of tweaking the code generated by swagger-codegen. I had to replace ActivityExecution by 'ActivityExecution' at several other places in the ActivityExecution class. Also, I've seen that this is not enough because it creates a typing.ForwardRef instance, which is not handled by the framework when it tries to deserialize actual data, AFAIK. Then, I've made this hack in util.py:

def _deserialize(data, klass):
    ...
    elif isinstance(klass,typing.ForwardRef):
        from models import ActivityExecution
        return deserialize_model(data, klass._evaluate(globals(),locals()))

This replaces the ForwardRef into the actual ActivityExecution class. This is quite ugly but it works!

I presume that codegen developers could find a neater solution.

[dtrieschnigg]

For the __init__ you describe, you could use the quoted ActivityExecution and for the other references (which are /in/ a method definition) you could use global references.
Something like

import swagger_server.models

And in the methods using the classes
swagger_server.models.ClassName

This does prevent a circular reference.
You are working on the generated python server code? (I am trying to get the client-code running)

[dtrieschnigg]

@wing328 did you just send me an e-mail about this issue?

[frankyjuang]

Hi do we have expected timeline for this? also bumped into the same issue. Can help if needed.

[piedenis]

@dtrieschnigg Sorry for this (very) late answer! Thanks for the trick! BTW, yes, I use the generated server code only.

[vkushnarev]

@dtrieschnigg when I try to do like you suggested, I get an error:
AttributeError: module 'swagger_server' has no attribute 'models'

p.s. This method does work for one model and does not for another.

The object in swagger:

User:
    type: "object"
    properties:
      id:
        type: "integer"
        format: "int64"
      name:
        type: "string"
      manager:
        $ref: "/definitions/User"

And I have a few objects with such a refenence.

[dtrieschnigg]

@dtrieschnigg when I try to do like you suggested, I get an error:
AttributeError: module 'swagger_server' has no attribute 'models'

Do you have some kind of namespacing in your models? Can you check the generated code? Are you generating the client or the server?

[dtrieschnigg]

Ok, moving to https://github.com/openapitools/openapi-generator solved my problems....