Conditional validation type

[OldSneerJaw]

Feature Request

Description

Currently each property or element can be defined with only one validation type (e.g. string, integer, datetime, etc.). However, there are cases where it may be beneficial to allow a value to be one of several types (e.g. a date as either an ISO 8601 date/time string or as a Unix timestamp) while still being able to set some constraints on them.

Add a new validation type (e.g. conditional) that selects one of several different validators to apply to a property or element based on some condition (specified as a function).

Examples

propertyValidators: {
  date: {
    type: 'conditional',
    required: true,
    skipValidationWhenValueUnchangedStrict: true,
    validationCandidates: [
      {
        condition: function(doc, oldDoc, currentItemEntry, validationItemStack) {
          return typeof currentItemEntry.itemValue === 'string';
        },
        validator: {
          type: 'datetime',
          minimumValue: '1970-01-01T00:00Z'
        }
      },
      {
        condition: function(doc, oldDoc, currentItemEntry, validationItemStack) {
          return typeof currentItemEntry.itemValue === 'number';
        },
        validator: {
          type: 'integer',
          minimumValue: 0
        }
      }
    ]
  }
}

[dkichler]

Addressed by #39