Reference to local files (with relative/no path) doesn't work

[sblask]

I am trying to create a json schema (draft 4) which uses definitions from another file and includes them using $ref. I don't have any URL set up for the definitions file and I wasn't planning on doing that. I thought "$ref": "definitions.json#a_definition" (definitions.json lying in the same directory) would be enough, but I get a "No such file or directory" error.

I am not sure this should work, but this: http://code.google.com/p/jsonschema2pojo/wiki/Reference#$ref suggests it should ("$ref" : "user.json"). Googling/reading the draft didn't get me anywhere.

Using file://absolute/path/to/json/file does work, but that would be super ugly. Is there a better way to do what I want to do? Or is this something that needs fixing?

[Julian]

Hey!

The ref resolution code is pretty simple. Mostly it just delegates.

I haven't looked at it in a bit, but what I'd assume is going on is that relative refs will be resolved relative to the working directory, not relative to the schema file they came from.

Is that the behavior you're seeing? If not, I'll give this a try later when I get to a computer.

This at least should be documented, but I have to think about which is correct.

Oh and if you want you can use the store argument to just specify which schema you mean with your ref. That's probably easiest.

[gazpachoking]

I suspect this would probably work if the base uri was set to file:///wherever/yourschema.json, without this information, the ref resolver doesn't know what your relative refs are relative to. Not sure right now the best way to specify the base uri, I'll have to take a closer look later.

[sblask]

I figured I could write my own resolver if I really wanted too or add a handler, but as I said, I am not sure whether it should work out of the box or not (i.e. does the spec allow this or not). The store option seems a little hacky as I won't ever have actual URIs, but that could work and would be fairly easy indeed.

@Julian the code uses urllib2.urlopen which doesn't support relative paths at all, no matter what the current working directory is and if I omit the file:// it doesn't want to do anything. urllib.urlopen would work though, at least if the right working directory is set

@gazpachoking "wherever" would have to be absolute as well then? :-/ Obviously the references should be relative to the current file, but as the code uses a json object directly and doesn't read the file itself, we don't know where the current file is. Without changing that it would be fairly complicated to change that I guess. And changing that would break backwards compatibility...

[gazpachoking]

Yeah, you are going to have to specify the absolute path that relative paths should be judged on no matter what, as jsonschema is not the one loading from the disk, so it doesn't know what the location of the schema is. I think something of this nature will work:

schema = json.load(open("/path/to/schema"))
resolver = RefResolver.from_schema(schema, base_uri="file:///path/to/schema")
validator = Draft4validator(schema, resolver=resolver)

[gazpachoking]

Whether there could/should be a better way, not sure. Maybe @Julian has some input on that.

[gazpachoking]

I'm also making another tool right now to make dealing with json references easier (mostly outside of json schema, but it could be used with it as well) https://github.com/gazpachoking/jsonref

It isn't quite ready for use yet, but it will have the advantage of also handling refs that are not subschemas.

schema = jsonref.load(open("/wherever/schema"), base_uri="file:///wherever/schema", jsonschema=True)
# Then it can be used anywhere without worrying about refs e.g.
jsonschema.validate(someinstance, schema)

[Julian]

If urllib does not resolve things without schemes, that would seem to
indicate that those are not valid URIs, which I guess I kind of was
assuming.

JSON Schema doesn't define any special semantics for "$ref" other than
"it's a URI under the relevant spec", so if that's the case, I revert to my
previous suggestion and would think the current behavior is likely to be
correct (and that the schema you're copying from is wrong or outdated,
which is quite common for schemas with refs I've seen in the wild).

I think you'd need to have some other canonical name for the resource
you're locating.

[gazpachoking]

@Julian Would it be good for IValidator to take a base_uri keyword argument (that would be passed to the RefResolver)? It seems like it might be a common enough need to allow setting it without instantiating a RefResolver yourself.

[Julian]

Well it's not like it requires much effort to instantiate a resolver :p...

(Keeping stuff separate is good if we need/want to change the API in some
way later, it requires fewer things to change).
On May 6, 2013 5:20 PM, "Chase Sterling" notifications@github.com wrote:

@Julian https://github.com/Julian Would it be good for IValidator to
take a base_uri keyword argument (that would be passed to the RefResolver)?
It seems like it might be a common enough need to allow setting it without
instantiating a RefResolver yourself.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/98#issuecomment-17509002
.

[gazpachoking]

Yep, sounds fine.

[sblask]

Thank you for your help! I got it to work now:

with open(os.path.join(absolute_path_to_base_directory, base_filename)) as file_object:
    schema = json.load(file_object)
resolver = jsonschema.RefResolver('file://' + absolute_path_to_base_directory + '/', schema)
jsonschema.Draft4Validator(schema, resolver=resolver).validate(data)

RefResolver.from_schema did not work , because the base_uri is taken from the schema's id - which I don't define. My schema looks something like this now:

{
    "$schema": "http://json-schema.org/draft-04/schema",
    "type": "object",
    "properties": {
        "something_referencing_a_local_file": {"$ref": "another_file.json#a_definition"}
    }
}

Not sure what people who do define id have to do to test locally, using the store option might be the best.

[Julian]

Glad you got it working :). That looks about right to me.

[jiaj0000]

Hi,
I am sorry for asking this issue again after one year. I have the same question regarding validating $ref with relative path.

http://stackoverflow.com/questions/25145160/json-schema-ref-does-not-work-for-relative-path/25147381?noredirect=1#comment39166721_25147381

I really hope you can help me with it.

After reading this post, I am assuming that I have to have absolute path somewhere(like in the resolver..) if I wanna use relative path for $ref?

@Julian

Thank you in advance!