Data module

Contains generic interfaces for data access components as well as abstract implementations for in-memory and file persistence.

Important points

The persistence components come in two kinds. The first kind is a basic persistence that can work with any object types and provides only minimal set of operations. The second kind is so called “identifieable” persistence with works with “identifable” data objects, i.e. objects that have unique ID field.
The identifiable persistence provides a full set or CRUD operations that covers most common cases.

Packages

The module contains the following packages:

Core - interfaces for data access components.
Persistence - in-memory and file persistence components, as well as JSON persister class.

Use

Install the NPM package as

npm install pip-services3-data-nodex --save

As an example, lets implement persistence for the following data object.

import { IIdentifiable } from 'pip-services3-commons-nodex';

export class MyObject implements IIdentifiable {
  public id: string;
  public key: string;
  public value: number;
}

Our persistence component shall implement the following interface with a basic set of CRUD operations.

export interface IMyPersistence {
    getPageByFilter(correlationId: string, filter: FilterParams, paging: PagingParams): Promise<DataPage<MyObject>>;
    
    getOneById(correlationId: string, id: string): Promise<MyObject>;
    
    getOneByKey(correlationId: string, key: string): Promise<MyObject>
    
    create(correlationId: string, item: MyObject): Promise<MyObject>;
    
    update(correlationId: string, item: MyObject): Promise<MyObject>;
    
    deleteById(correlationId: string, id: string): Promise<MyObject>;
}

To implement in-memory persistence component you shall inherit IdentifiableMemoryPersistence. Most CRUD operations will come from the base class. You only need to override getPageByFilter method with a custom filter function. And implement a getOneByKey custom persistence method that doesn’t exist in the base class.

import { IdentifiableMemoryPersistence } from 'pip-services3-data-nodex';

export class MyMemoryPersistence extends IdentifableMemoryPersistence {
  public constructor() {
    super();
  }

  private composeFilter(filter: FilterParams): any {
    filter = filter || new FilterParams();
    
    let id = filter.getAsNullableString("id");
    let tempIds = filter.getAsNullableString("ids");
    let ids = tempIds != null ? tempIds.split(",") : null;
    let key = filter.getAsNullableString("key");

    return (item) => {
        if (id != null && item.id != id)
            return false;
        if (ids != null && ids.indexOf(item.id) < 0)
            return false;
        if (key != null && item.key != key)
            return false;
        return true;
    };
  }
  
  public async getPageByFilter(correlationId: string, filter: FilterParams, paging: PagingParams): Promise<DataPage<MyObject>> {
      return await super.getPageByFilter(correlationId, this.composeFilter(filter), paging, null, null);
  }  
  
  public async getOneByKey(correlationId: string, key: string): Promise<MyObject> {
    let item = this._items.find(item => item.key == key);
    
    if (item != null) {
      this._logger.trace(correlationId, "Found object by key=%s", key);
    } else {
      this._logger.trace(correlationId, "Cannot find by key=%s", key);
    }
    
    return item;
  }

}

It is easy to create file persistence by adding a persister object to the implemented in-memory persistence component.

import { ConfigParams } from 'pip-services3-commons-nodex';
import { JsonFilePersister } from 'pip-services3-data-nodex';

export class MyFilePersistence extends MyMemoryPersistence {
  protected _persister: JsonFilePersister<MyObject>;

  constructor(path?: string) {
      super();
      this._persister = new JsonFilePersister<MyObject>(path);
      this._loader = this._persister;
      this._saver = this._persister;
  }

  public configure(config: ConfigParams) {
      super.configure(config);
      this._persister.configure(config);
  }
}

Configuration for your microservice that includes memory and file persistence may look the following way.

...
{{#if MEMORY_ENABLED}}
- descriptor: "myservice:persistence:memory:default:1.0"
{{/if}}

{{#if FILE_ENABLED}}
- descriptor: "myservice:persistence:file:default:1.0"
  path: {{FILE_PATH}}{{#unless FILE_PATH}}"../data/data.json"{{/unless}}
{{/if}}
...