Demgel Validation Decorators

What is this?

There are times when you want to validate an object and assure that all properties are valid values.

Example

import {ValidationModel, Model, isNumber, isString} from "@demgel/validation";

@Model
export class SomeModel extends ValidationModel {
    @required()
    @isNumber()
    aNumber: number;

    @required()
    @isString()
    aString: string;
}

To check that a model is valid just use isValid().

if (someModel.isValid()) {
    // Do something with the data...
} else {
    // report Error
    this.errors.forEach((error, message) => {
        console.log(`${error}: ${message}`);
    };
}

If there is an error the model will contain a property called errors. errors is a Map<string, string>.

Custom Validators

You can write your own validators by using the generateValidator function.

returning null equals no error, returning a string will set the validator to error.

export declare function generateValidator(name: string, validator: any): (target: Object, propertyKey: string) => void;

export var someValidator = (options) => generateValidator("someValidator", (value) => {
    // Check the value to see if it matches
    if (valueisnotgood) {
        return "Value is not right";
    }
    return null;
}

export var anotherValidator = generateValidator("anotherValidator", (value) => {
    // Check the value to see if it is correct
    return null;
}

The first example, someValidator, would be used like this:

@Model()
export class SomeClass extends ValidatableModel {
    @someValidator("somepassedinvalue")
    property: string;
}

The second example, anotherValidator, would be used like this:

@Model()
export class SomeClass extends ValidatableModel {
    @anotherValidator
    property: string;
}

Parsing Object/JSON into/from Models

TO JSON

You should (and probably best) use the obj.toJSON() function from a ValidationModel to convert a Model to JSON. There are some underlying functions and values that should not be serialized, such as error.

Also there is a decorator that you can use excludeJSON that will let you mark properties that should be excluded from the JSON output.

@Model()
export class JSONClass extends ValidatableModel {
    @excludeJSON()
    property: string;
    aprop: number;
}

let cla = new JSONClass();
cla.property = 'something';
cla.aprop = 42;

cla.toJSON();

This will output:

{"aprop": 42}

notice the excluded property of property is not included.

FROM JSON/Object

@Model()
export class ClassWithProperties extends ValidatableModel {
    @required()
    prop: string;
    another: number;
    array: SomeType[];
}

Call your api and get this JSON string back.

{
    "prop": "a string",
    "another": 42,
    "array": ["value", "anothervalue"]
}

const jsonString = (api call returned value);

let classWithProperties = new ClassWithProperties();
classWithProperties.fromJSON(jsonString);
// classWithProperties is not populated with values from jsonString

// If you needed to parse the jsonString first
let obj = JSON.parse(jsonString);
classWithProperties.fromObject(obj);
// classWithProperties is now populated with values from obj