Custom validation rules

If predefined validation rules do not cover the requirements, then custom validation rules are needed. A new validation rule can be created inheriting the ValidationRule class. Each rule requires a descriptive and preferably unique name. The name identifies the rule in the collection of broken rules. The business-objects library follows the practice that the class name of the validation rule is the name of the rule and the appended Rule string.

The parameters of the rule definition are passed in the constructor of the new rule:

  • primaryProperty
    Required PropertyInfo object.
    The definition of the property the rule relates to.
  • arg1, arg2, ...
    Additional parameters required by the rule to check the validation of the value of the primary property.
  • message
    Optional string. The rule has to provide a default message.
    Human-readable description of the failure of the rule, or the key of the localizable description.
  • priority
    Optional integer. The default value is 10.
    The priority of the rule, greater number means higher priority. The rules of a property are evaluated in descending order of the priority.
  • stopsProcessing
    Optional Boolean. The default value is false.
    Indicates whether processing of the rules for a property stops when the rule fails.

If the rule needs one or more additional business object properties to check the validation of the value of the primary property, then these properties can be added to the collection of input properties using the addInputProperty() method. If the rule - depending on the conditions - requires checking or rechecking the validation of one or more additional business object properties, then these properties can be added to the collection of affected properties using the addAffectedProperty() method. Other parameters are to be stored in properties of the validation rule object itself.

Each validation rule has to be initialized in the constructor using the standard parameters.

The custom validation rules has to override the execute() method of the base object. The logic of the validation is implemented in that method. The method has one argument that is an array of the values of the 'input' properties. It contains at least the value of the primary property. If validation succeeds the method simply returns, otherwise it returns a ValidationResult object using result() method to indicate the failure of the checking.

See API reference for the detailed description of ValidationRule's methods.


The following example shows a custom validation rule that ensures the value of the primary property is not null (and not empty in case of Text data type) only when another property has a specified value:

'use strict';

var util = require('util');
var bo = require('business-objects');
var t = bo.i18n('', 'CustomRules');
var ValidationRule = bo.rules.ValidationRule;
var RuleSeverity = bo.rules.RuleSeverity;

// Constructor of RequiredIfRule class.
function RequiredIfRule (primaryProperty, conditionProperty, conditionValue, message, priority, stopsProcessing) {
  // Define the name of the rule., 'RequiredIf');

  // Save the condition value.
  this.conditionValue = conditionValue;

  // Add the condition property to the input properties to retrieve its value.

  // Initialize base properties.
      message || t('requiredIf',,, conditionValue),
      priority || 45,

  // Immutable object.
util.inherits(RequiredIfRule, ValidationRule);

// Override execute() method.
RequiredIfRule.prototype.execute = function (inputs) {

  // Get property values.
  var value = inputs[];
  var condition = inputs[];

  // Check the condition.
  if (condition === this.conditionValue) {
    // Check the property value.
    if (!this.primaryProperty.hasValue(value))
      // Return a result object that indicates the failure of the rule.
      return this.result(this.message, RuleSeverity.error);

module.exports = RequiredIfRule;

The default.json file in the directory of locales contains the default error message when the validation fails:

  "CustomRules": {
    "requiredIf": "Property {0} is required when the value of property {1} is {2}.",