AngularFire2: Perform 'Joins' on FirebaseListObservables using RxJS .map()
As stated in another question, I'm developing an Ionic 2 App using Firebase as Backend.
I have categories and I have products. Products belong to categories. As it is a "n to m" relationship, products and categories are stored in separate nodes in firebase. I structured the data as follows:
Categories know, which products belong to them (keys are referenced in "prods" node of each category). Products know, which categories they belong to (keys are referenced in the "prod_cat" node). However, when I list all categories I just know the IDs of the products which belong to the category. In the template I need to show more details, like the product name for example.
I read many similar questions an came up with this solution to add the product information to the categories:
getProductsOfCategory(catId){
this.productsOfCategory = this.af.database.list('/categories/'+catId+'/prods');
return this.productsOfCategory
.map(products => {
console.log(products); // works fine: an object containing the relevant product information is logged to the console (see screenshot)
products.map( product => { console.log(product.$key); // works fine: the IDs of the products are logged to the console
product.prod_details = this.af.database.object('/products/'+product.$key); // seems not to work. Returned value: undefined
});
});
Unfortunately, this doesn't work. As written as comments in the code, the product information are collected correctly and logged to the console (see following screenshot): console screenshot
However, the returned object of the above function is "undefined".
When I try to state, that explicitely an object of type FirebaseListObservable is to be returned, I receive the error:
Type 'Observable' is not assignable to type 'FirebaseListObservable'. Property '$ref' is missing in type 'Observable'.
Does anybody have an idea what else I could try?
Thank you very much in advance!
Answers:
I solved the problem.
provider (*.ts):
getProductsOfCategory(catId){
let result = this.af.database.list('/categories/'+catId+'/prods')
.map(items => {
for (let product of items) {
this.af.database.object('/products/'+product.$key)
.subscribe( data => {
product.details = data;
});
}
return items;
})
return result;
}
getCategoriesAndProducts(){
let result = this.af.database.list('/categories')
.map(items => {
for (let category of items) {
this.getProductsOfCategory(category.$key)
.subscribe(data => {
category.productDetails = data;
})
}
return items;
})
return result;
}
provider call in the tempaltes ts-file:
getCategoriesAndProducts(){
this.categoryService.getCategoriesAndProducts()
.subscribe(data => {
this.categoriesAndProducts = data;
});
template / view (*.html):
<ng-container *ngFor="let cat of categories">
<ng-container *ngIf="cat.parent_cat === 'noParentCategory'">
<h3>
{{cat.cat_name}}
</h3>
<ng-container *ngFor="let subcat of categoriesAndProducts">
<ion-list>
<ng-container *ngIf="subcat.parent_cat === cat.$key">
<ion-item-divider>
{{subcat.cat_name}}
</ion-item-divider>
<ion-item *ngFor="let prod of subcat.productDetails">
{{prod.details?.prod_name}}
</ion-item>
</ng-container>
</ion-list>
</ng-container>
</ng-container>
</ng-container>