How to get a full list of loopback4 models to evaluate custom decorator metadata at boot time? - loopbackjs

Question

I'm currently migrating a loopback3 application to loopback4. I've annotated the properties in my loopback4 models with a custom typescript decorator with some metadata.
How can I get a full list of models and evaluate their metadata at boot time?
I did some experiments with LifeCycleObserver, but did not find a way how to get notified when all models are ready nor get a list of them.
Here is an simplified example of the metadata i want to process. Please note: #propertyAcl is a custom decorator.
export class Model1 extends AuditMixin(SoftdeleteMixin(AbstractEntity)) {
// ...
#property()
#propertyAcl({
'role1': Permission.READ_WRITE,
'role2': Permission.READONLY,
})
myproperty?: string;
// ...
}
I need to configure the external library accesscontrol with the metadata at boot time. The idea is to create property based acls per model.

Answer 1

How can I get a full list of models and evaluate their metadata at boot time?
Overview
Using #loopback/metadata to create a Decorator and define / get the metadata via MetadataInspector.
Create a DecoratorFactory "A"
Create a Context "B"
Overide the mergeWithInherited function in "A", and in this function we store (define) the metadata of the property that you annotated at design time to "B"
Create a Decorator "C" via "A"
Annotate any properties you want with "C"
Get the metadata in "B" at runtime
Step 1 2 3 4
// 1
class A extends PropertyDecoratorFactory<object> {
constructor(key: string, spec: object, options?: DecoratorOptions | undefined) {
super(key, spec, options);
}
// 3
mergeWithInherited(inheritedMetadata: MetadataMap<object>, target: Object, propertyName?: string, descriptorOrIndex?: TypedPropertyDescriptor<any> | number): any {
// define metadata to "B"
MetadataInspector.DesignTimeReflector.defineMetadata(`${target.constructor.name}.${propertyName}`, this.spec, B);
}
}
// 2
export const B = new Context("B.context");
// 4
export function C(spec: object): PropertyDecorator {
return A.createDecorator<object>(
'C.decorator',
spec,
);
}
Step 5
class ModelFoo extends Model {
#property({
type: 'string'
})
p1?: string;
#C({ metadata: "this is ModelFoo" })
#property({
type: 'string'
})
p2?: string;
}
class ModelBar extends Model {
#property({
type: 'string'
})
p1?: string;
#C({ metadata: "this is ModelBar" })
#property({
type: 'string'
})
p2?: string;
}
Step 6
function Test() {
// get all metadata keys in "B"
let keys: string[] = MetadataInspector.DesignTimeReflector.getMetadataKeys(B);
// output >>>> [ 'ModelFoo.p2', 'ModelBar.p2' ]
console.log(keys);
// get metadata with 'ModelFoo.p2' in "B"
let metadata = MetadataInspector.DesignTimeReflector.getMetadata(keys[0], B);
// output >>>> { metadata: 'this is ModelFoo' }
console.log(metadata);
// do somthing...
}