'$id' property usage in JSON Schema

json jsonschema json-schema-validator
sevenwithawp picture sevenwithawp · Oct 10, 2017 · Viewed 8.4k times · Source

I'm using JSON Schema for validating data.

I think that I may have a mistake on my schema by using the reserved keywords $id. The intention of this field was to designate what the REMOTE ID of the property on another platform was. So it was the "origin ID".

Can you please advise what $id is and if I have made a critical mistake and this value needs changing. Because in the documentation I have found this definition:

If present, the value for this keyword MUST be a string, and MUST represent a valid URI-reference [RFC3986]. This value SHOULD be normalized, and SHOULD NOT be an empty fragment <#> or an empty string <>.

Answer

Pedro picture Pedro · Oct 10, 2017

$id is a reserved keyword.

It serves for:

  • Declaring an identifier for the schema or subschema
  • Declaring a base URL against which $ref URLs are resolved

You can identify a schema, or a part of your schema (a subschema) by using $id, and then you can reuse it somewhere else by using the $ref keyword. The most simple way of seeing this, is that the $ref would be replaced by the schema with the corresponding id.

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