docs: snippets

docs/SUMMARY.md

@@ -36,6 +36,8 @@
   - [Style Guide](recipes/style-guide.md)
   - [Unit Testing](recipes/unit-testing.md)
   - [RxAngular Integration](recipes/intregration-with-rxangular.md)
+- Snippets
+  - [State Operators](snippets/operators.md)
 - Plugins
   - [Introduction](plugins/intro.md)
   - [CLI](plugins/cli.md)

docs/advanced/operators.md

@@ -224,6 +224,10 @@ function addEntity(entity: Entity): StateOperator<EntitiesStateModel> {
 
 As you can see, state operators are very powerful to start moving your immutable state updates to be more declarative and expressive. Enhancing the overall maintainability and readability of your state class code.
 
+## Snippets
+
+Check this [section]() for more operators that you can add to your application.
+
 ## Relevant Articles
 
 [NGXS State Operators](https://medium.com/ngxs/ngxs-state-operators-8b339641b220)

docs/snippets/operators.md

@@ -0,0 +1,47 @@
+# State Operators Snippets
+
+In this section you will find state operators that didnt make it to the library but can be very helpful in your app.
+
+## upsertItem
+
+Inserts or updates an item in an array depending on whether it exists.
+
+### Usage
+
+```ts
+ctx.setState(
+  patch<FoodModel>({
+    foods: upsertItem<Food>(f => f.id === foodId, food)
+  })
+);
+```
+
+### State Operator Code
+
+```ts
+import { Predicate } from '@ngxs/store/operators/internals';
+import { StateOperator } from '@ngxs/store';
+import { compose, updateItem, iif, insertItem, patch } from '@ngxs/store/operators';
+
+export function upsertItem<T>(
+  selector: number | Predicate<T>,
+  upsertValue: T
+): StateOperator<T[]> {
+  return compose<T[]>(
+    items => <T[]>(items || []),
+    iif<T[]>(
+      items => Number(selector) === selector,
+      iif<T[]>(
+        items => selector < items.length,
+        <StateOperator<T[]>>updateItem(selector, patch(upsertValue)),
+        <StateOperator<T[]>>insertItem(upsertValue, <number>selector)
+      ),
+      iif<T[]>(
+        items => items.some(<any>selector),
+        <StateOperator<T[]>>updateItem(selector, patch(upsertValue)),
+        <StateOperator<T[]>>insertItem(upsertValue)
+      )
+    )
+  );
+}
+```