How to specify a property can be null or a reference

[Daniel Popowich]

I've seen a lot of talk on github issues regarding swagger's lack of support for oneOf and anyOf. Setting aside the merits of the arguments over there, I'm looking for a practical solution to the problem of a response object (or any object, really) that has a property that can be EITHER another object, or null.  This is a real-world problem for my project: complex objects reference other objects, but in some cases, the referenced object is NULL, i.e, some parent objects do not point to a child and null is the appropriate value in these cases.

I'm surprised the spec doesn't handle this readily.  There is x-nullable, provided by some consumers of the spec, but that does not work in conjunction with $ref, where the reference replaces the object wholesale, leaving the x-nullable setting ignored.

I think I asked the question well over on stackoverflow, maybe someone here can earn some points over there:

http://stackoverflow.com/questions/40920441/how-to-specify-a-property-can-be-null-or-a-reference-with-swagger

[tony tam]

Hi, we are adding the oneOf and anyOf support in 3.0, and I believe the “nullable” support is being added as well.

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[Daniel Popowich]

On Friday, December 2, 2016 at 12:05:24 PM UTC-5, tony tam wrote:

Hi, we are adding the oneOf and anyOf support in 3.0, and I believe the “nullable” support is being added as well.

In other words, there's no way in 2.0 to specify a property of an object may be either NULL or a $ref?

[tony tam]

I think you’re describing that a value can be “null” or an “object”, forgetting specification semantics.  That would be done with the “required” flag unless I’m misunderstanding something thing.

[Daniel Popowich]

tony tam writes:
> I think you re describing that a value can be null or an object , forgetting
> specification semantics. That would be done with the required flag unless I m
> misunderstanding something thing.

I'm talking about response objects, a returned object may be:

{
"id": 12345,
"name": "John Doe",
"foo": {...a complex object...}
}

Think RDB where column foo is a reference to another table and
nullable. I always want to return "foo" to the clients, so its either
null or the complex object (the serialization of the row from the
other table).

And because a Foo is a complex object I want to create a definition of
it and reference it, keeping my spec DRY:

{
"properties": {
"id": {
"type": "integer"
},
"name": {
"type": "string"
},
"foo": {
"$ref": "#/definitions/Foo"
}
},
type: "object"
}

With oneOf, I can make foo:

"foo": {
oneOf: [
{"$ref": "#/definitions/Foo"},
{"type": "null"}
]
}

How can I do this now?

[Toe Dipper]

I am also curious for support for "nullable" fields.  Support for "oneOf" and "anyOf" is not quite the same thing.  In JSON Schema, the "type" field can be an array, e.g. to indicate a nullable field:

// In JSON Schema
{
   "type": ["string", "null"]
}
// Or, using anyOf
{
   "anyOf":[
      {"type": "string"},
      {"type": "null"}
   ]
}

The end result is equivalent to "anyOf"... arguably the JSON Schema spec should simplify so that the type is always a string and "anyOf" is the only way to support this "string OR null" value.

To clear, the "required" keyword does not cover this specific use case where a property needs to exist, but its value might need to be null.

Relatedly, the "swagger-cli" npm package DOES consider the type: ["string", "null"] as valid, but the online editor does not.  Which is correct?

[Ron Ratovsky]

“null” is not a valid type in swagger, nor is “anyOf” or multi-types.

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