Using negative lookbehind with jsonschema

Question

I'm using Node 9.2.0 and ajv 6.0.0.

I have a schema that I wish to use negative lookbehind on, it's defined like:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "release format",
    "description": "A Release Format",
    "type": "object",
    "properties": {
        "id": {"type": "integer"},
        "title": {
            "anyOf": [
                {
                    "type": "string",
                    "pattern": "^((?!itunes).)*$"
                },
                {
                    "type": "string",
                    "pattern": "^((?!exclusive).)*$"
                },
                {
                    "type": "string",
                    "pattern": "^((?!ringtone).)*$"
                }
            ]
        }
    }
}

However, it appears that when I try and validate this with AJV using the following data: {"id": 123, "title": "world exclusive"} I don't get a validation error.

The code:

const Ajv = require('ajv');
class Validator {
  constructor() {
    this.releaseFormatSchema = JSON.parse(fs.readFileSync('./schemas/release-format.json'));
    this.schemaValidator = new Ajv({allErrors: true});
  }

  validate(data) {
    let validate = this.schemaValidator.compile(this.releaseFormatSchema);
    let valid = validate(data);
    console.log(valid);
    console.log(validate);
  }
}

where data would be: {"id": 123, "title": "world exclusive"}. I would expect this to error, however it's currently telling me that the data is valid.

`(?!..)` is a negative lookahead, but I get your drift. It all can be combined with `^((?!a|b|c|d).)*$`, etc. which also matches the empty string. — , Jan 23 '18 at 17:59
`However, it appears that when I try and validate this with AJV using the following data: {"id": 123, "title": "world exclusive"} I don't get a validation error.` That's looks to be because it is matching one of the regex that doesn't have `exclusive` in it. Combining into a single regex will solve the problem — , Jan 23 '18 at 18:05
crap, doesn't help if i'm getting my terms confused... but if you have an answer where it would error on titles containing `exclusive`, `itunes` and `ringtone` please let me know. — Jarede, Jan 23 '18 at 18:06
Yeah, try this _single_ regex: `^((?!itunes|exclusive|ringtone).)*$`, errors on an OR (not and) condition. — , Jan 23 '18 at 18:08

score 0 · Accepted Answer · answered Jan 24 '18 at 08:19

The answer was also found by @sln and @ClasG, anyOf does a union between titles patterns can match : "all except strings which contains itunes" union "all except strings which contains exclusive" union "...", which means all which not contains all the forbidden keywords. It can be fixed either

using allOf instead of anyOF

"title": {
    "allOf": [
        {
            "type": "string",
            "pattern": "^((?!itunes).)*$"
        },
        {
            "type": "string",
            "pattern": "^((?!exclusive).)*$"
        },
        {
            "type": "string",
            "pattern": "^((?!ringtone).)*$"
        }
    ]
}

using single type/pattern :

"title": {
    "type": "string",
    "pattern": "^((?!itunes|exclusive|ringtone).)*$"
}

Using negative lookbehind with jsonschema

1 Answers1