Properties based on enum value in JSON Schema

Question

I'm building a json schema definition which has a fixed set of controls that I've currently limited with an enum. However, not all properties are relevant for all controls.

I only want to require an options property if the controlType = dropdown

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "controlType": {
        "type": "string",
        "enum": ["title", "dropdown", "button"]
      },
      "options:": {
        "type": "array",
        "items": {"type": "string"}
      }
    }
  }
}

How can I conditionally include / require a field in a json schema?

Answer 1

Use IF..Then..Else ^{new in Draft-07}

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "controlType": {
        "type": "string",
        "enum": ["title", "dropdown", "button"]
      },
      "options:": {
        "type": "array",
        "items": {"type": "string"}
      }
    },
      
    "if": {
      "properties": {
        "controlType": {"const": "dropdown"}
      }
    },
    "then": {
      "required": ["options"]
    }
  }
}

Use oneOf or anyOf

This can be useful if you have a property that has a limited number of acceptable values (such as an enum), but each possible value needs to be individually mapped.

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "controlType": {
        "type": "string",
        "enum": ["title", "dropdown", "button"]
      },
      "options:": {
        "type": "array",
        "items": {"type": "string"}
      }
    },  
    "anyOf": [
      {
        "properties": {
          "controlType": {"const": "dropdown"}
        },
        "required": ["controlType", "options"]
      },
      {
        "properties": {
          "controlType": {"const": "title"}
        },
        "required": ["controlType"]
      },
      {
        "properties": {
          "controlType": {"const": "button"}
        },
        "required": ["controlType"]
      }
    ]
  }
}

Further Reading

• Conditionally require attribute
• Applying subschemas conditionally
• Combining schemas