# NgRx Advanced (Angular)

> Entity adapter, feature states, meta-reducers, router store, component store, effects patterns, error handling

- 24 interview questions
- Senior
- [Interview Questions: Angular](https://sharpskill.dev/en/technologies/angular/interview-questions.md)

## 1. What is the main role of createEntityAdapter in NgRx?

**Answer**

The Entity Adapter automatically generates reducers and selectors to manage normalized collections of entities. It provides methods like addOne, addMany, updateOne, removeOne that facilitate manipulation of ID-indexed objects. This avoids manually writing collection management logic and ensures a normalized state for better performance.

## 2. What data structure does Entity Adapter use to store entities?

**Answer**

Entity Adapter stores entities in an object with two properties: ids (ordered array of identifiers) and entities (key-value dictionary for O(1) access). This normalized structure avoids duplicates, facilitates updates by ID and optimizes lookup performance. The ids array maintains display order.

## 3. How to specify a custom sort comparator with Entity Adapter?

**Answer**

The sort comparator is defined via the sortComparer property when creating the adapter. This function compares two entities and returns a number (negative, zero or positive) to determine their order. If sortComparer is set to false, no automatic sorting is applied and ids maintain insertion or update order.

## 21 more questions available

- Which Entity Adapter method to use to add or update multiple entities in a single operation?
- Which predefined Entity Adapter selector retrieves all entities as an array?

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