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Overview

When defining a model in LoopBack 4, property types are the important part. No matter whether it is for defining properties with decorator @property or defining a model at runtime, you may want to specify the types in the definition. The following is a typical property definition:

Defining a property with the decorator

@property({
  type: 'string',
  require: true,
  // other fields
})
userName: String;

Defining a model at runtime

const UserDef = new ModelDefinition('User')
  .addProperty('id', {type: 'number', id: true})
  .addProperty('userName', {type: 'string'});

The following table summarizes LoopBack types.

Type Description Example
any Any type, including array, object, Date, or GeoPoint Any of: true, 123, "foo", [ "one", 2, true ]
array

JSON array

See Array types below.

 [ "one", 2, true ]
Boolean JSON Boolean true
buffer Node.js Buffer object 
new Buffer(42);
date JavaScript Date object

new Date("December 17, 2003 03:24:00");
GeoPoint

LoopBack GeoPoint object

 
new GeoPoint({lat: 10.32424, lng: 5.84978});
Date

LoopBack DateString object

"2000-01-01T00:00:00.000Z"

"2000-01-01"

"2000-01-01 12:00:00"
null JSON null null
number JSON number

3.1415
Object

JSON object or any type

See Object types below.

 
{ "userName": "John89", "age": 25, "vip": false}
String JSON string "LoopBack"

In general, a property will have undefined value if no explicit or default value is provided.

Array types

The following are examples of how you can define array type properties:

  @property({
    type: 'array',
    itemType: 'string',
    length: 20,
  })
  strAry?: string[]; // e.g ['can', 'only', 'contain', 'strings']

  @property({
    type: 'array',
    itemType: 'number',
  })
  numAry?: number[]; // e.g [42, 998, 1]

  @property({
    type: 'array',
    itemType: 'any',
  })
  anyAry?: any[]; // e.g ['LoopBack', 4, true]

  @property({
    type: 'array',
    itemType: 'object',
  })
  ObjAry?: object[]; // e.g [{'Nodejs': 'LoopBack'}]

Object types

Use the Object type when you need to be able to accept values of different types, for example a string or an array.

A model often has properties that consist of other properties. For example, the user model can have an address property that is in type Address, which has properties street, city, state, and zipCode:

@model()
export class Address extends Entity {
  @property({
    type: 'number',
  })
  id: number;

  // street, city, state, zipCode proper definitions ..
}

@model()
export class User extends Entity {
  // other props

  @property({
    type: 'object',
  })
  address: Address;
}

The value of the address is the definition of the Address type.