Json schema regex

Question

I am building a json request schema at the moment. One of my constraints in the schema is that there value of firstLetter should ONLY contain 1 character, lowercase or uppercase. I tried the following (its a snippet of the schema):

"firstLetter": {
        "id": "/properties/firstLetter",
        "maxLength": 1,
        "minLength": 1,
        "pattern": "[a-z][A-Z]",
        "type": "string"
    }

but it doesn't seem to work. I would also like the regex to have the rule that there should only be 1 character

Try "^[a-zA-Z]$" or (if it is used in XSD Schema later) "[a-zA-Z]" — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 5, 2017 at 10:22
@lualover, did my answer work for you? If yes, please consider accepting. Else, please let know of the results. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 5, 2017 at 18:05

Community · Accepted Answer · 2020-06-20 09:12:55Z

4

Acc. to 6.8. pattern section of JSON Schema Validation: A Vocabulary for Structural Validation of JSON:

The value of this keyword MUST be a string. This string SHOULD be a valid regular expression, according to the ECMA 262 regular expression dialect.

A string instance is considered valid if the regular expression matches the instance successfully. Recall: regular expressions are not implicitly anchored.

You may use

"pattern": "^[a-zA-Z]$"

It will match exactly 1-letter strings, only consisting of an ASCII letter.

Note that maxLength and minLength become redundant with this regex validation, so you may minify the code to

"firstLetter": {
    "id": "/properties/firstLetter",
    "pattern": "^[a-zA-Z]$",
    "type": "string"
}

edited Jun 20, 2020 at 9:12

CommunityBot

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answered May 5, 2017 at 10:28

Wiktor Stribiżew

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3 Comments

lualover2017 Over a year ago

So would the schema throw a validation error if for example someone sent a request like "firstLetter":"ab"

Wiktor Stribiżew Over a year ago

I updated the pattern as per this JSON Schema 1.0 documentation and JSON Schema.

Wiktor Stribiżew Over a year ago

Now, I think it is complete. Sorry, I just mistook the JSON schema with XML Schema at first.

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