defining schema for a schema #736

rashmy-git · 2024-05-28T21:00:21Z

rashmy-git
May 28, 2024

Hi,
I have previously used simple features of JSON schema to validate my JSON data.
Now, I'm exploring the option of defining a JSON schema to validate another JSON schema.

In my service, I want to allow the user to create any kind of business object. Say the example of blog post from here.

POST/create-data

{
  "title": "New Blog Post",
  "content": "This is the content of the blog post...",
  "publishedDate": "2023-08-25T15:00:00Z",
  "author": {
    "username": "authoruser",
    "email": "[email protected]"
  },
  "tags": ["Technology", "Programming"]
}

But before any data is created, I'd like my user to give me the JSON schema for their business object. So the JSON schema for the above data would look like this:

POST /define-schema

{
  "$id": "https://example.com/blog-post.schema.json",
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "description": "A representation of a blog post",
  "type": "object",
  "required": ["title", "content", "author"],
  "properties": {
    "title": {
      "type": "string"
    },
    "content": {
      "type": "string"
    },
    "publishedDate": {
      "type": "string",
      "format": "date-time"
    },
    "author": {
      "$ref": "https://example.com/user-profile.schema.json"
    },
    "tags": {
      "type": "array",
      "items": {
        "type": "string"
      }
    }
  }
}

Now when they give me the schema, how can I allow the user to include the below in the JSON schema?

A sibling of "properties" called "deploy-region" with keys "primary" and "secondary", where primary has enum [us-east, us-west]
Can I extend "type" to have additional values like "businessObjectType" apart from the standard values [object, string, number, boolean etc..]

Basically, I want to create a schema for a schema.

With my limited search, I could not find good answers. If there is any documentation or previous references please point me to them.

Thank you!

jdesrosiers · 2024-06-05T23:57:18Z

jdesrosiers
Jun 5, 2024
Maintainer

A schema that validates a schema is known as a "meta-schema". Meta-schemas are just schemas. They can be a little mind bending to write, but you can write them just like you would write any other schema.

For example, here's a constraint that requires that there's properties keyword has a deploy-region property.

{
  "properties": {
    "properties": {
      "required": ["deploy-region"]
    }
  }
}

properties in this example shows how things can get confusing when writing meta-schemas.

So, using my example, see if you can expand it to express the rest of your constraints. If you're still having trouble, post what you've tried and we'll try to nudge you in the right direction.

Also, sorry it took so long for someone to respond. Our whole team was traveling last week and we've gotten a bit behind.

0 replies

rashmy-git · 2024-06-14T20:26:11Z

rashmy-git
Jun 14, 2024
Author

Thank you for the reply!

I'm trying to wrap my head around vocabularies and connecting it with dialect :)
I've made an attempt at it, but the problem is that when using it ajv to validate, it fails.

Here is what I have:

Example JSON Instance Data

{
	"deployapi": "1.0",
	"title": "class-of-2024-blogs",
	"blogs": {
		"blog-schemas": {
		  "ScienceBlogs": {
			"type": "object",
			"properties": {
			  "topic": {
				"type": "string",        //REUSE all fields available in JSON schema 'properties'
				"minLength": 10,
				"maxLength": 128,
				"pattern": "^[a-zA-Z0-9]*$",
				"example": "Dark Matter",
				"primary-key": true      //NEW field, that should be available within properties
			  },
			  "writers": {
				"type": "array",
				"items": {
				  "type": "string"
				},
				"example": ["Jack", "Jill"]
			  },
			  "content": {
				"type": "string",
			  },
			  "publish-date": {
				"type": "string",
				"format": "date-time",
			  }
			},
			"required": ["topic", "writers", "content", "publish-date"],
			"additionalProperties": false
			"deploy-region": "us-east",   //NEW field, that should be available as sibling to properties
			"owner-contact": {            //NEW field, that should be available as sibling to properties
				"email": "[email protected]"
			}
		  },
		  "TheatreBlogs": {
			"type": "object",
			"properties": {
			  "title": {
				"type": "string",
				"primary-key": true
			  },
			  "writers": {
				"type": "array",
				"items": {
				  "type": "string"
				}
			  },
			  "actors": {
				"type": "array",
				"items": {
				  "type": "string"
				}
			  },
			  "genre": {
				"type": "string",
				"enum": ["comedy", "historical"]
			  }
			  "synopsis": {
				"type": "string",
			  },
			  "publish-date": {
				"type": "string",
				"format": "date-time",
			  }
			},
			"required": ["topic", "writers", "actors", "synopsis", "publish-date"],
			"additionalProperties": false
			"deploy-region": "us-west",
			"owner-contact": {
				"email": "[email protected]"
			}
		  },
		}
	}
}

My schema

{
	"$schema": "https://myorganization/meta-schema#",
	"$id": "https://myorganization/blog-schema##",


	"type": "object",
	"properties": {
		"deployapi": {
		  "type": "string",
		  "pattern": "^1\\.\\d+(-.+)?$"
		},
		"title": {
		  "type": "string"
		},
		"blogs": {
		  "$ref": "#/$defs/blogModel"
		},
		"required": [ "deployapi", "title", "blogs"]
		"additionalProperties": false
	}
	"$defs": {
		"blogModel": {
			"type": "object",
			"properties": {
				"blog-schemas": {
				  "type": "object",
				  "properties": {
					"deploy-region": {
					  "$ref": "#/$defs/deployRegion"
					},
					"owning-team": {
					  "$ref": "#/$defs/owningTeam"
					}
				  }
 				  "required": ["deploy-region", "owning-team"],
				  "additionalProperties": {
					"$dynamicRef": "#meta"
				  }
				}
			}
		}
		"deployRegion": {
		   "type": "string"
		   "enum": ["us-east", "us-west"]
		},
		"owningTeam": {
			"type": "object",
			"properties": {
				"contact-name": {
					"type": "string"
				},
				"contact-email": {
					"type": "string"
				}
			},
			"required": ["contact-email"],
			"additionalProperties": false
		},
	}
}

My meta-schema

{
	"$schema": "https://myorganization/meta-schema#", 
	"$id": "https://myorganization/meta-schema#",
	"$vocabulary": {
		"https://json-schema.org/draft/2020-12/vocab/core": true,
		"https://json-schema.org/draft/2020-12/vocab/applicator": true,
		"https://json-schema.org/draft/2020-12/vocab/validation": true,
		"https://json-schema.org/draft/2020-12/vocab/meta-data": true,
		"https://json-schema.org/draft/2020-12/vocab/format-annotation": true,
		"https://json-schema.org/draft/2020-12/vocab/content": true,
		"https://myorganization/myorganization-vocab": true
	},
	"$dynamicAnchor": "meta",

	"type": ["object", "boolean"],
	"properties": {
		"example": true,
		"primary-key": {
		   "type": "boolean"
		}
	}
}

Questions:
[1]
When using AJV code to validate, with the above schema and JSON, it is failing.

ajv.addMetaSchema( /**Added My meta-schema **/ )
const validate = ajv.compile( /**Provide My schema **/ )
validate( /**Provide Example JSON Instance data **/ )

[2]
Do I need to use dialect as well?
If there is dialect, vocabulary, meta-schema how do I provide these to ajv?
Should I use bundling to generate a single meta-schema and then provide this to ajv validator?

Thanks for your time and guidance!

4 replies

jdesrosiers Jun 18, 2024
Maintainer

It looks like you have several errors in your schema. Any one of them could be causing you issue with ajv. Ajv doesn't support $vocabulary, but that probably doesn't matter in your case. All you really need is the custom meta-schema.

Here are the issues I found.

You are missing commas in several places. Use a JSON validator to find these.
required and additionalProperties are in the wrong place in the top of your schema. They should be after properties not inside it.
You're using "$dynamicRef": "#meta" without a $dynamicAnchor. What do you expect this to resolve to?

jdesrosiers Jun 18, 2024
Maintainer

It looks like you don't want a dynamic reference at all. I think this is what you want.

"blogModel": {
  "type": "object",
  "properties": {
    "blog-schemas": {
      "type": "object",
      "additionalProperties": {
        "type": "object",
        "properties": {
          "deploy-region": {
            "$ref": "#/$defs/deployRegion"
          },
          "owning-team": {
            "$ref": "#/$defs/owningTeam"
          }
        },
        "required": ["deploy-region", "owning-team"]
      }
    }
  }
}

jdesrosiers Jun 18, 2024
Maintainer

Actually, probably this,

"blogModel": {
  "type": "object",
  "properties": {
    "blog-schemas": {
      "type": "object",
      "additionalProperties": {
        "$ref": "https://myorganization/meta-schema",
        "properties": {
          "deploy-region": {
            "$ref": "#/$defs/deployRegion"
          },
          "owning-team": {
            "$ref": "#/$defs/owningTeam"
          }
        },
        "required": ["deploy-region", "owning-team"]
      }
    }
  }
}

rashmy-git Jul 18, 2024
Author

Thank you for all your suggestions. I'll use the latest one you suggested and test out my scenarios.

Sorry for the late reply, I was out.

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

JSON Schema

defining schema for a schema #736

{{title}}

Replies: 2 comments 4 replies

{{title}}

{{title}}

{{title}}

{{title}}

{{title}}

{{editor}}'s edit

{{editor}}'s edit

{{title}}

Select a reply

JSON Schema

defining schema for a schema #736

rashmy-git May 28, 2024

Replies: 2 comments · 4 replies

jdesrosiers Jun 5, 2024 Maintainer

rashmy-git Jun 14, 2024 Author

Example JSON Instance Data

My schema

My meta-schema

jdesrosiers Jun 18, 2024 Maintainer

jdesrosiers Jun 18, 2024 Maintainer

jdesrosiers Jun 18, 2024 Maintainer

rashmy-git Jul 18, 2024 Author

rashmy-git
May 28, 2024

Replies: 2 comments 4 replies

jdesrosiers
Jun 5, 2024
Maintainer

rashmy-git
Jun 14, 2024
Author

jdesrosiers Jun 18, 2024
Maintainer

jdesrosiers Jun 18, 2024
Maintainer

jdesrosiers Jun 18, 2024
Maintainer

rashmy-git Jul 18, 2024
Author