json schema validation. How can I accept an array or null?

Question

We have implemented json schema validation (using newtonsoft) on our rest layer. It's really made a difference, but I have a question of possibility and how to.

For a specific property, the following is valid (according to the product owner):

.... choices: [] .......

.... choices: ["hello", "world"]

.... choices: null .....

here is a whittled down example of the json schema definition

{
   'description': 'myDescription',
   'type': 'object',
   'properties':
    {
     'name': {'type':'string', 'required': true},
     'description': {'type':'string'},
     'choices': {'type': 'array', 
         'items': {'type': 'string'}}
}

Obviously the first 2 examples pass validation, but the latter fails with "expecting an array" error.

The property is optional.

As an aside, if anyone has a good link to the full set of documentation on json schema definitions, I'd love to get it. I have not found a good single source, but I am sure there is one.

Thank you.

-r

evanmcdonnal · Accepted Answer · 2013-07-09 17:31:28Z

27

You can specify an array of possible types like so;

"myProperty": { "type": [ "array", "null" ], "required":false }

The json will pass validation if "myProperty" is of any type in the type's array. I set required to false because you said this was an optional property, that will only make it pass if the property is not present in the json. If you have required set to false and the property is in the json but of the wrong type, validation will fail.

These are the best docs on json schemas that I know of; http://json-schema.org/latest/json-schema-validation.html The site lacks useful examples but any details that you need will be in the docs.

edited Jul 9, 2013 at 17:31

answered Jul 9, 2013 at 17:24

evanmcdonnal

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4 Comments

Roger Joys Over a year ago

Thank you. This solved the issue. I also discovered 'type':'any' which was also useful in some of our properties where the type was dependent on some other attributes of the payload.

Roger Joys Over a year ago

In further googling, I found this which was also helpful and had some better examples: tools.ietf.org/html/draft-zyp-json-schema-03

evanmcdonnal Over a year ago

@RogerJoys yeah I've looked at that. If you post other json schema questions on SO I'll likely answer them. They're pretty under utilized so there isn't a ton of information on them but I've been using them for a bit so I know at least all of the basics plus a few other tricks.

RedX Over a year ago

This answer is for draft 3. in 4 and later the requirements are an array that go on the parent element. github.com/json-schema/json-schema/wiki/ChangeLog#required

Karl Anderson · Accepted Answer · 2013-07-09 17:23:32Z

1

Have you tried making the default value for choices be []?

I am assuming, since you said the property is optional, that you are using the optional parameter syntax in C# or am I incorrect?

answered Jul 9, 2013 at 17:23

Karl Anderson

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