# Property Constraints

# Intro

@model()
export class Person extends Model {
  @property @mock('name') public name: string;
  @property @min(1) @max(50) public age: number;
  @property @length(250) public bio: string;
  @property public gender?: "male" | "female" | "other";
}

Now we turn our attention to providing meta-information to the individual properties. There are two aspects to focus on:

Properties - each property is defined as a public member of the class, given a type (via TypeScript grammar), and denoted as a property with the @property decorator.
Constraints - all other decorators attached to the property are there to associate additional meta-information about the property for your run-time environment to respond to.

# Categories

While there aren't stark differences in behavior between these constraints it might be worthwhile drawing up some categories:

# Responsive Meta

This cateogory is meta-information which Firemodel not only stores but also behaviorly responds to.

The @mock decorator allows for detailed meta-characteristics of your data to be stored in your models and then mocked whenever you need them. See the mocking section for more details.
The @defaultValue decorator allows you to state values for some of your model's properties to take on if they are not specified. Unlike the mock these values are not used for testing purposes but rather for real life defaults. This allows your models to initialize into a known state without requiring the caller to state every required property any time they are adding/creating a new record.
```
export FooBar extends Model {
  @property @defaultValue("USA") country: string;
}
```
The @pushKey decorator tells firemodel that the given property is a dictionary/hash which conforms to Firebase's normal "array representation" (aka, a dictionary whose keys are Firebase generated keys derived from the Firebase push function). This is very useful when you have multiple clients who might be pushing content to the same "firebase array" because using the Firebase push operation ensures that any and all updates are serialized and that the new keys have a natural sort order based on time that they were received (many people don't know that embedded into the Firebase key is a precise datetime stamp which measures down to the milisecond)

# Built-in Meta

These constraints are built into Firemodel "out of the box" and therefore immediately available to your code as in import but they are not enforced by FireModel. The enforcement is left to you in your implementation.

Examples are min, max, length, and desc. For instance, to get the minimum age in our Person example above:

if(age > person.META.property('age').min) { ... }

# Your Meta

The final category of property meta is that which you add yourself. This can be done one of two ways:

there is a built-in decorator called @constrain(prop: string, value: any) which lets you associate any name/value pair with a property.
you can also add your own decorator by creating something like this:

import {propertyDecorator} from 'firemodel';
export function foobar(value: any) {
  return propertyDecorator({ foobar: value });
}

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