JSON schema conditional dependency on value

Question

I know there is a similar question here, but it didn't really address my issue. In short, I want one my fields to be dependent on the other field's value. But for some values, I don't want any field to be required. Here is an example:

Schema

{
  "definitions": {},
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {

    "colour": {
      "type": "string",
      "enum": ["red", "black", "blue"]
    },

    "blackQuote": {
      "type": "string",
      "maxLength": 11
    },

    "redQuote": {
      "type": "string",
      "maxLength": 11
    }
  },

  "oneOf": [
      {
        "properties": {
          "colour": {"enum": ["red"]}
        },
        "required": ["redQuote"]
      },
      {
        "properties": {
          "colour": {"enum": ["black"]}
        },
        "required": ["blackQuote"]
      }
  ],

  "required": [
    "colour"
  ]
}

This works like this:

IF the colour is "red" THEN "redQuote" (but not "blackQuote") is required: this is fine
IF the colour is "black" THEN "blackQuote" (but not "redQuote") is required: this is also fine
BUT if I put the colour "blue" in my JSON, then the validator says that the properties "redQuote" and "blackQuote" are missing... I don't want that, I only want dependecies for "red" and "black", but if the colour is "blue" I don't want anything required. How to achieve this?

Did you try adding one more schema to oneOf? Which does not require anything and has other enum values for colour. In this case "blue"? — Ganesh, Dec 05 '17 at 08:53

Jason Desrosiers · Answer 1 · 2021-06-03T19:02:42.413

You can do this with a boolean logic concept called implication (!A or B). It can be used like an "if-then" statement. For example, either "color" is not "red" or "redQuote" is required. Any time I need to use this, I break it down with definitions so it reads as nice as possible.

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {
    "colour": { "enum": ["red", "black", "blue"] },
    "blackQuote": { "type": "string", "maxLength": 11 },
    "redQuote": { "type": "string", "maxLength": 11 }
  },
  "allOf": [
    { "$ref": "#/definitions/red-requires-redQuote" },
    { "$ref": "#/definitions/black-requires-blackQuote" }
  ],
  "required": ["colour"],
  "definitions": {
    "red-requires-redQuote": {
      "anyOf": [
        { "not": { "$ref": "#/definitions/is-red" } },
        { "required": ["redQuote"] }
      ]
    },
    "black-requires-blackQuote": {
      "anyOf": [
        { "not": { "$ref": "#/definitions/is-black" } },
        { "required": ["blackQuote"] }
      ]
    },
    "is-red": {
      "properties": {
        "colour": { "enum": ["red"] }
      },
      "required": ["colour"]
    },
    "is-black": {
      "properties": {
        "colour": { "enum": ["black"] }
      },
      "required": ["colour"]
    }
  }
}

score 6 · Answer 2 · answered Dec 27 '17 at 21:18

Simplest answer in draft-04 (as noted by Ganesh in a comment):

{
  "definitions": {},
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {

    "colour": {
      "type": "string",
      "enum": ["red", "black", "blue"]
    },

    "blackQuote": {
      "type": "string",
      "maxLength": 11
    },

    "redQuote": {
      "type": "string",
      "maxLength": 11
    }
  },

  "oneOf": [
      {
        "properties": {
          "colour": {"enum": ["red"]}
        },
        "required": ["redQuote"]
      },
      {
        "properties": {
          "colour": {"enum": ["black"]}
        },
        "required": ["blackQuote"]
      },
      {
        "properties": {
          "colour": {"enum": ["blue"]}
        }
      }
  ],

  "required": [
    "colour"
  ]
}

I think @jason's answer is slightly better. This way requires you to re-specify blue as a possible value. By using "implication" (explained in his answer), that is avoided. — Alexander Bird, Sep 13 '18 at 20:45

score 5 · Answer 3 · answered Dec 05 '17 at 09:33

If you move the specifics of what you want into the OneOf's then you can keep it all pretty simple, especially if you end up with a load of other values for color.

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "type": "object",
    "oneOf": [
        {
            "type": "object",
            "properties": {
                "colour": {
                    "type": "string",
                    "enum": [
                        "red"
                    ]
                },
                "redQuote": {
                    "type": "string",
                    "maxLength": 11
                }
            },
            "required": [
                "redQuote"
            ]
        },
        {
            "type": "object",
            "properties": {
                "colour": {
                    "type": "string",
                    "enum": [
                        "black"
                    ]
                },
                "blackQuote": {
                    "type": "string",
                    "maxLength": 11
                }
            },
            "required": [
                "blackQuote"
            ]
        },
        {
            "type": "object",
            "properties": {
                "colour": {
                    "type": "string",
                    "enum": [
                        "blue"
                    ]
                }
            }
        }
    ],
    "definitions": {}
}

Thanks, that's a great answer! However, one more detail that is bugging me. What if I want to be able to have a field "redQuote", no matter if field "colour" is present? Now it's ok, if the field "colour" equals "red" then "redQuote" is required. But I also want a JSON with only a field "redQuote" (without the field "colour") to also pass a validation. So if no "colour" is specified, then there is no requirement for the "redQuote" field and it can freely be there. How is that possible? — wesleyy, Dec 06 '17 at 21:22

JSON schema conditional dependency on value

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