A mixin to enable computed (dynamic) properties for loopback Models
This is a mixin for the LoopBack framework that adds computed properties to a model.
A computed property is a property of which the value is set dynamically after reading model data from the data source.
loaded
observer.ctx.instance
.ctx.isNewInstance
.npm install --save loopback-ds-computed-mixin
Add the mixins property to your server/model-config.json:
{
"_meta": {
"sources": [
"loopback/common/models",
"loopback/server/models",
"../common/models",
"./models"
],
"mixins": [
"loopback/common/mixins",
"../node_modules/loopback-ds-computed-mixin/lib",
"../common/mixins"
]
}
}
To use with your Models add the mixins
attribute to the definition object of your model config.
The property you want to compute has to be defined in the model. The callback can be a promise too.
{
"name": "Item",
"properties": {
"name": "String",
"description": "String",
"status": "String",
"readonly": "boolean"
},
"mixins": {
"Computed": {
"properties": {
"readonly": "computeReadonly"
}
}
}
}
On your model you have to define the callback method.
// Set an item to readonly if status is archived
Item.computeReadonly = function computeReadonly(item) {
return item.status === 'archived';
};
Run the tests in test.js
npm test
Run with debugging output on:
DEBUG='loopback:mixin:computed' npm test