ISSUE #1 | delete records | use dictionary to maintain records instead of array. resolve delete issues. add tsdoc

Author: cmwhited

lib/services/in-memory-db.service.ts

@@ -3,37 +3,144 @@ import { InMemoryDBEntity } from '../interfaces';
 
 @Injectable()
 export class InMemoryDBService<T extends InMemoryDBEntity> {
-  public records: T[] = [];
+  private recordMap: { [id: number]: T } = {};
 
+  /**
+   * Given the array of records of type `T`, reduce the array into a dictionary object of
+   * type `{ [id: number]: T }`. Set the value of the `recordMap` to this reduced input array.
+   * Example:
+   *
+   * - input array
+   * ```json5
+   * [
+   *  {
+   *    "id": 1,
+   *    "prop": "test1"
+   *  },
+   *  {
+   *    "id": 2,
+   *    "prop": "test2"
+   *  }
+   * ]
+   * ```
+   * - becomes
+   * ```json5
+   * {
+   *    1: { "id": 1, "prop": "test1" },
+   *    2: { "id": 2, "prop": "test2" }
+   * }
+   * ```
+   * @param records the array of records of type T
+   */
+  set records(records: T[]) {
+    if (!records || records.length === 0) {
+      this.recordMap = {};
+    }
+    this.recordMap = records.reduce(
+      (previous: { [id: number]: T }, current: T) => {
+        return {
+          ...previous,
+          [current.id]: current,
+        };
+      },
+      this.recordMap,
+    );
+  }
+  get records(): T[] {
+    return Object.keys(this.recordMap).map(key => this.recordMap[key]);
+  }
+
+  /**
+   * Add the supplied `record` partial to the `recordMap` in-memory data store of records.
+   * Get the `id` of the record by getting the next available `id` value.
+   * Returns the `id` of the newly added record.
+   * @param record the partial record of type `T` to create
+   */
   public create(record: Partial<T>): number {
     const id = record.id || this.getNextId();
     const newRecord: T = { ...record, id } as T;
-    this.records.push(newRecord);
+    this.recordMap = {
+      ...this.recordMap,
+      [id]: newRecord,
+    };
     return newRecord.id;
   }
 
+  /**
+   * Update a record in the `recordMap` of type `T` using the supplied record.
+   * @param record the record of type `T` to update
+   */
   public update(record: T): void {
-    const foundRecordIndex = this.records.findIndex(r => r.id === record.id);
-    this.records[foundRecordIndex] = { ...record };
+    this.recordMap = {
+      ...this.recordMap,
+      [record.id]: record,
+    };
   }
 
-  public delete(id: number) {
-    const foundRecordIndex = this.records.findIndex(r => r.id === id);
-    this.records.splice(foundRecordIndex);
+  /**
+   * Remove the record of type `T` from the `recordMap` using the supplied PK id.
+   * @param id the PK id of the record
+   */
+  public delete(id: number): void {
+    const { [id]: removed, ...remainder } = this.recordMap;
+    this.recordMap = {
+      ...remainder,
+    };
   }
 
+  /**
+   * Get a single record of type `T` with the supplid id value.
+   * @param id the PK id of the record
+   */
   public get(id: number): T {
-    return this.records.find(r => r.id === id);
+    return this.recordMap[id];
   }
 
+  /**
+   * Return all of the records of type `T`.
+   */
   public getAll(): T[] {
     return this.records || [];
   }
 
+  /**
+   * Return an array of records of type `T` filtered with the supplied predicate.
+   * Example:
+   * - given records:
+   * ```json5
+   * [
+   *  {
+   *    "id": 1,
+   *    "prop": "test1"
+   *  },
+   *  {
+   *    "id": 2,
+   *    "prop": "test2"
+   *  }
+   * ]
+   * ```
+   * - to find records with a `prop` value of `test1`:
+   * ```ts
+   * const records: T[] = service.query(record => record.prop === 'test1');
+   * ```
+   * @param predicate the filter predicate
+   */
   public query(predicate: (record: T) => boolean) {
     return this.records.filter(predicate);
   }
 
+  /**
+   * get the next id by finding the max id in the current records array and adding 1 to that value.
+   * Example:
+   * - current `recordMap`
+   * ```json5
+   * {
+   *    1: { "id": 1, "prop": "test1" },
+   *    4: { "id": 4, "prop": "test2" }
+   * }
+   * ```
+   * - next next id would be: `5` as the current highest id is `4` + `1` = `5`.
+   */
   private getNextId(): number {
     if (this.records && this.records.length > 0) {
       return Math.max(...this.records.map(r => r.id)) + 1;