Handle optional fields properly by not adding it to 'required' elements

[kdallmeyer-sr]

In json-schema, when a field is optional, it does not need to be added to the "required" field. Unfortunately the Avro -> Json-Schema converter currently makes every field required in the resulting schema. This means that in the JSON every field must be present and either set to null or populated. In reality we should mark JSON with optional fields removed as valid as well.

Demo Avro Schema

{
  "type" : "record",
  "name" : "Demo",
  "namespace" : "com.shoprunner.data.demo",
  "fields" : [ {
    "name" : "name",
    "type" : "string"
  }, {
    "name" : "count",
    "type" : [ "null", "int" ]
  }, {
    "name" : "price",
    "type" : [ "null", "float" ]
  } ]
}

Converted JSON schema with required optional fields that nullable.

{
  "definitions" : {
    "record:com.shoprunner.data.demo.Demo" : {
      "type" : "object",
      "required" : [ "name", "count", "price" ],
      "additionalProperties" : false,
      "properties" : {
        "name" : {
          "type" : "string"
        },
        "count" : {
          "oneOf" : [ {
            "type" : "null"
          }, {
            "type" : "integer",
            "minimum" : -2147483648,
            "maximum" : 2147483647
          } ]
        },
        "price" : {
          "oneOf" : [ {
            "type" : "null"
          }, {
            "type" : "number"
          } ]
        }
      }
    }
  },
  "$ref" : "#/definitions/record:com.shoprunner.data.demo.Demo"
}

JSON that is correctly validated with this schema

{
  "name" : "Bob",
  "count" : 1,
  "price" : 1.10
}

{
  "name" : "Bob",
  "count" : null,
  "price" : null
}

JSON that is incorrectly failed with this schema

{
  "name" : "Bob"
}

The change I am proposing will make the schema only require name:

{
  "definitions" : {
    "record:com.shoprunner.data.demo.Demo" : {
      "type" : "object",
      "required" : [ "name" ],
      "additionalProperties" : false,
      "properties" : {
        "name" : {
          "type" : "string"
        },
        "count" : {
          "oneOf" : [ {
            "type" : "null"
          }, {
            "type" : "integer",
            "minimum" : -2147483648,
            "maximum" : 2147483647
          } ]
        },
        "price" : {
          "oneOf" : [ {
            "type" : "null"
          }, {
            "type" : "number"
          } ]
        }
      }
    }
  },
  "$ref" : "#/definitions/record:com.shoprunner.data.demo.Demo"
}