Validating a json based on the input values

[sturaw]

Hi, I'm someone new to json schema and while going to the docs I've found that it has a lot of functionality, most of which are based on the keys in the json. I have a very specific requirement and was wondering if that would be possible to do directly through JSON schema (found an alternative where i would have to change the structure but I'd like to avoid that extra overhead.)
In the following JSON,

{
    "fruit": "apple",
    "locations": [
        {
            "name": "UK",
            "value": "UH"
        },
        {
            "name": "EU",
            "value": "OH"
        },
        {
            "name": "INDIA",
            "value": "HP"
        },
        {
            "name": "USA",
            "value": "All"
        },
        {
            "name": "USA1",
            "value": "ABC"
        },
        {
            "name": "USA2",
            "value": "ABC2"
        }

    ]
}

My requirement is that

1. ln 'locations', 'USA' should be a mandatory in input.
2. If the value of 'USA' is 'ALL' then, 'USA1' and 'USA2' should be mandatory.

Would appreciate any help.

[gregsdennis]

This can be done fairly easily if you're using a draft 7 or later.

What you want is going to be a combination of this StackOverflow answer and the contains keyword.

For (1)

You want at least one item to have name: USA.

contains alone solves this for you. contains defines a schema, and if the value is an array, it must contain at least one item that matches that schema. It doesn't matter where in the array the item is.

{
  ...
  "contains": {
    "type": "object",
    "properties": {
      "name": { "const": "USA" }
    },
    "required": [ "name" ]
  }
  ...
}

If you've already required that all of the items are objects with name and value, you can leave out the type and required from contains, but it doesn't hurt anything to overconstrain like this.

For (2)

You want a conditional that if the item with name: USA also has value: All, then your array must also contain an item with name: USA1 and another item with name: USA2.

First, for the conditional, you want to use if/then (else is also available, but you don't need it here).

if and then each define schemas. If the value passes the if schema, then it must also pass the then schema.

So for if, we check to see if there is an item with name: USA, value: All. This is very similar to what we have above.

{
  "if": {
    "contains": {
      "type": "object",
      "properties": {
        "name": { "const": "USA" },
        "value": { "const": "All" }
      },
      "required": [ "name", "value" ]
    }
  }
}

And for the then we check to see if both of the other items are there. To combine two contains keywords, we can use an allOf.

{
  "then": {
    "allOf": [
      {
        "contains": {
          "type": "object",
          "properties": {
            "name": { "const": "USA1" }
          },
          "required": [ "name" ]
        }
      },
      {
        "contains": {
          "type": "object",
          "properties": {
            "name": { "const": "USA2" }
          },
          "required": [ "name" ]
        }
      }
    ]
  }
}

Putting all of this together, you get:

{
  ...
  "contains": {
    "type": "object",
    "properties": {
      "name": { "const": "USA" }
    },
    "required": [ "name" ]
  },
  "if": {
    "contains": {
      "type": "object",
      "properties": {
        "name": { "const": "USA" },
        "value": { "const": "All" }
      },
      "required": [ "name", "value" ]
    }
  },
  "then": {
    "allOf": [
      {
        "contains": {
          "type": "object",
          "properties": {
            "name": { "const": "USA1" }
          },
          "required": [ "name" ]
        }
      },
      {
        "contains": {
          "type": "object",
          "properties": {
            "name": { "const": "USA2" }
          },
          "required": [ "name" ]
        }
      }
    ]
  }
  ...
}

[handrews]

I'll just add to Greg's excellent answer that if you're using draft-06 or earlier, you can still do this, but you have to use different keywords. Using {A}, {B}, {C} as placeholder schemas because I'm lazy, this draft-07+ structure:

{
  "if": {A},
  "then": {B},
  "else": {C}
}

becomes this in draft-06 and earlier:

{
  "oneOf": [
    "allOf": [{A}, {B}],
    "allOf": [{"not": {A}}, {C}]
  ]
}

And if you're using draft-04 (which hopefully you aren't), then you have to replace "const": "foo" with "enum": ["foo"]