Rules handle validation and business logic. Their Execute method is called on each property changed of the defined trigger properties.

  • Rules can modify the Entity
  • If any Rules assign a message to a property the Entity.IsValid is set to False
    • If an Entity has any child Entities that have IsValid=False the Parent Entity has IsValid=False as well
  • Rules are cascading. Changes to Entity within a Rule will trigger the modified property’s Rules

This is a brief overview of a Neatoo Rule to be used with an Entity using UniqueNameRule as an example.

Class Declaration

internal class UniqueNameRule : AsyncRuleBase<IPerson>, IUniqueNameRule
  • Inherit from AsyncRuleBase<T> for Async Task Rules and RuleBase<T> otherwise
  • T is the target of the rule. In this case the target T is IPerson
  • For shared rules use a common interface as the type T.

Constructor

    private UniqueName.IsUniqueName isUniqueName;

    public UniqueNameRule(UniqueName.IsUniqueName isUniqueName) : base()
    {
        this.isUniqueName = isUniqueName;
        AddTriggerProperties(p => p.FirstName, p => p.LastName);
    }
  • Dependency Injection is fully supported
  • AddTriggerProperties - Expressions to specify which Entity property changed will trigger the rule.
    • In this case changes to IPerson.FirstName and IPerson.LastName will trigger Rule.Execute

Execute Method

    protected override async Task<IRuleMessages> Execute(IPerson t, CancellationToken? token = null)
  • On Rule Execute the target instance is sent in
  • Properties on the target can be changed
    • Rules are cascading. Changing properties on the Target will trigger any assigned Rules

Rule Messages

                return None;
                ...
                return (new[]
                {
                    (nameof(t.FirstName), "First and Last name combination is not unique"),
                    (nameof(t.LastName), "First and Last name combination is not unique")
                }).AsRuleMessages();
  • Return None to specify no validation errors
  • Return RuleMessages to specify validation errors
    • RuleMessage is a (property, message) pair
    • There are a number of overrides including here where Tuple<string, string>[] is being transformed to RuleMessages
  • A property may have multiple validation messages