Generate JSON Schema from sample JSON data in C# with NJsonSchema

Question

I am hoping this is me not holding it right, but I am trying to generate a JSON schema from a JSON string that I have in memory.

I am using the NJsonSchema off of GitHub. https://github.com/NJsonSchema/NJsonSchema/

string json = @"{
  ""a"": 1,
  ""name"": ""Bill Smith"",
  ""isTall"": true
}";

var schemaItem = JsonSchema4.FromJson(json);
string jsonSchema = schemaItem.ToJson();

When I execute the code above I get the following value in jsonSchema which is not correct.

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "a": 1,
  "name": "Bill Smith",
  "isTall": true
}

I have created a GitHub bug for it for the time being just in case. https://github.com/NJsonSchema/NJsonSchema/issues/180

Rico Suter · Accepted Answer · 2018-11-05 20:33:18Z

3

In the current version of NJsonSchema you can generate a JSON Schema from sample data:

See https://github.com/RSuter/NJsonSchema/wiki/SampleJsonSchemaGenerator

The commit: https://github.com/NJsonSchema/NJsonSchema/commit/28d5a1357a9b5a3367154d3bc6e2488769b721aa

Will be available in version v7.6.

The DataToJsonSchemaGenerator: https://github.com/NJsonSchema/NJsonSchema/blob/master/src/NJsonSchema/Generation/DataToJsonSchemaGenerator.cs

I think there's also a FromJsonData method on JsonSchema4....

edited Nov 5, 2018 at 20:33

answered Jan 11, 2017 at 21:09

Rico Suter

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Karl-Johan Sjögren · Accepted Answer · 2016-08-27 14:36:43Z

1

You are using it wrong, JsonSchema4.FromJson(string json) is used to load existing schema json, not loading arbitrary json and generating a schema from it.

What you might be looking for is JsonSchema4.FromType<MyType>() which can generate a schema from a type, though you would need to have actual types for everything then.

As far as I can tell there isn't any way to generate a schema from just json so you'll need to create a class that matches your input. If you need that then you can have a look at http://www.newtonsoft.com/jsonschema, though it is not a free solution (and I'm in no way affiliated with it).

answered Aug 27, 2016 at 14:36

Karl-Johan Sjögren

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3 Comments

Jerrod Horton Over a year ago

Thanks for the response. Unfortunately creating types for my json objects is not something I have the opportunity to do with the application for which I am using it. I am looking to do exactly what this does: jsonschema.net/#. I have an object represented in JSON and I want the associated JSON Schema. Also, It seems that JsonSchema4.FromUrl(validUrlWithJson) works how I would expect as well. It takes the JSON from that URL and seems to create a schema from it.

Karl-Johan Sjögren Over a year ago

Just had a look at the source for JsonSchema4.FromUrl and all it does it is fetch data from a url and then pass it to JsonSchema4.FromJson so it won't help you. I'm afraid that you might need to code this one yourself though it shouldn't be that hard to do since json just have a few types for you to handle (string, int, bool, possibly date).

Jerrod Horton Over a year ago

Yeah thanks. I was hoping something would do it for me so I didn't have to run the risk of meaaibg up the schema from hand building it.

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