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

Add this to your package’s pubspec.yaml file:

dependencies:
  pip_services3_data: version

Now you can install package from the command line:

pub get

For example, you need to implement persistence for a data object defined as following.

import 'package:pip_services3_commons/src/data/IIdentifiable.dart';

class MyObject implements IIdentifiable<String> {
  @override
  String? id;
  String key;
  String value;

  Dummy({String? id, String key, String value})
      : id = id,
        key = key,
        content = content;

  void fromJson(Map<String, dynamic> json) {
    id = json['id'];
    key = json['key'];
    content = json['content'];
  }
}

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

abstract class IMyPersistence {
    void getPageByFilter(String correlationId, FilterParams filter, PagingParams paging);
    
    getOneById(String correlationId, String id);
    
    getOneByKey(String correlationId, String key;
    
    create(String correlationId, MyObject item);
    
    update(String correlationId, MyObject item);
    
    deleteById(String correlationId, String id);
}

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 'package:pip_services3_data/src/persistence/IdentifiableMemoryPersistence.dart';
import 'package:pip_services3_commons/src/data/FilterParams.dart';
import 'package:pip_services3_commons/src/data/PagingParams.dart';

class MyMemoryPersistence extends IdentifiableMemoryPersistence {
  MyMemoryPersistence(): super() {}

  composeFilter(FilterParams filter) {
    filter = filter != null ? filter : FilterParams();
    
    String id = filter.getAsNullableString("id");
    String tempIds = filter.getAsNullableString("ids");
    List<String> ids = tempIds != null ? tempIds.split(",") : null;
    String 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;
    };
  }
  
  Future<DataPage<MyData>> getPageByFilter(String correlationId, FilterParams filter, PagingParams paging){
    return super.getPageByFilterEx(correlationId, composeFilter(filter), paging, null);
  }  
  
  Future<String> getOneByKey(String correlationId, String key) {
    
    final item =
      this._items.firstWhere((item) =>
          item.name == item.key == key,
          orElse: () {
            return null;
    });
    
    if (item != null) {
      this._logger.trace(correlationId, "Found object by key=%s", key);
    } else {
      this._logger.trace(correlationId, "Cannot find by key=%s", key);
    }
  }
}

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

import 'package:pip_services3_commons/src/config/ConfigParams.dart';
import 'package:pip_services3_data/src/persistence/JsonFilePersister.dart';


class MyFilePersistence extends MyMemoryPersistence {
  JsonFilePersister<MyObject> _persister;

  MyFilePersistence([String path]):super(){
    this._persister = new JsonFilePersister<MyObject>(path);
    this._loader = this._persister;
    this._saver = this._persister;
  }

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