JSON schema to allow date or empty string

Question

I need to define a JSON schema wherein the input can either be a date or empty string.

My current JSON schema is

{
    "type": "object",    
    "required": [        
        "FirstName",        
        "DateOfBirth"
    ],
    "properties": {
        "FirstName": {
            "type": "string"
        },        
        "DateOfBirth": {            
            "type": "string", 
            "format": "date"
        }
    }
}

This allows

{    
    "FirstName": "Alex",
    "DateOfBirth": "1980-10-31"
}

but not

{    
    "FirstName": "Alex",
    "DateOfBirth": ""
}

How can I define the JSON schema so that DateOfBirth allows dates as well as empty string.

I'm consuming the JSON message. The application that publishes the JSON message sends an empty string if DateOfBirth data is not present. I have no control over that. I was looking to see if I can get the JSON message validated using a JSON schema. — A B, Apr 28 '20 at 15:47

score 7 · Accepted Answer · answered May 04 '21 at 19:14

Use anyOf to allow for an empty string:

{
  "type": "object",
  "required": [
    "FirstName",
    "DateOfBirth"
  ],
  "properties": {
    "FirstName": {
      "type": "string"
    },
    "DateOfBirth": {
      "anyOf": [
        {
          "type": "string",
          "format": "date"
        },
        {
          "type": "string",
          "maxLength": 0
        }
      ]
    }
  }
}

JSON schema to allow date or empty string

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