@denis_bruns/base-database-service NPM

@denis_bruns/base-database-service

A foundational TypeScript library for building customizable database services with typed queries, filter expressions, and pagination.

Overview

@denis_bruns/base-database-service provides an abstract base class and utility functions to help developers implement clean, consistent database access layers across various data stores (e.g., SQL, NoSQL). It leverages filter expressions, pagination, and type-safe queries for a robust, extensible approach.

This package is part of the larger @denis_bruns ecosystem of libraries that emphasize clean architecture, testability, and modularity.

Key Features

Base Database Service
- An abstract class to derive your own database services.
- Handles pagination, filtering, and query preparation.
Filter Expression Builder
- An abstract class for translating filters (IFilterQuery) into a store-specific query format.
- Extendable for DynamoDB, MongoDB, SQL, or other implementations.
Pagination and Validation
- Built-in helpers (calculatePaginationValues, validatePagination) to keep pagination safe and consistent.
- validateValue function to detect potential NoSQL injections or invalid fields.
Separation of Concerns
- IQueryExecutor interface to separate query building from query execution.
- Clean architecture approach that fosters testability and maintainability.

Installation

Install via npm:

npm install @denis_bruns/base-database-service

Or via yarn:

yarn add @denis_bruns/base-database-service

Basic Usage

Below is a simplified example showing how to extend BaseDatabaseService and build a custom expression builder.

1. Create Your Expression Builder

import {
  BaseExpressionBuilder,
  IFilterQuery,
  IDatabaseExpression,
} from '@denis_bruns/web-core-ts';

// Custom expression interface
export interface MyExpression extends IDatabaseExpression {
  filterExpression: string;
  expressionValues: Record<string, any>;
}

// Extend the base expression builder to handle your filters
export class MyExpressionBuilder extends BaseExpressionBuilder<MyExpression> {
  buildFilterExpression(filters: IFilterQuery[]): MyExpression {
    // Example of building a simple 'field = value' expression
    const filterExpression = filters
      .map((f, idx) => `${f.field} ${f.operator} :val${idx}`)
      .join(' AND ');

    const expressionValues = filters.reduce((acc, f, idx) => {
      return { ...acc, [`:val${idx}`]: f.value };
    }, {});

    return { filterExpression, expressionValues };
  }
}

2. Create Your Query Executor

import { IQueryExecutor } from '@denis_bruns/web-core-ts';
import { MyExpression } from './MyExpressionBuilder';

export class MyQueryExecutor implements IQueryExecutor<MyExpression, any> {
  constructor(private readonly dataSource: any[]) {
    // 'dataSource' could be an array (for testing) or a real database client
  }

  async executeQuery(params: MyExpression, _client: any): Promise<any[]> {
    // This is just a mock example; you'd integrate with your real DB logic
    // For demonstration, let's just return the full dataSource:
    return this.dataSource;
  }
}

3. Extend `BaseDatabaseService`

import {
  BaseDatabaseService,
  IGenericFilterQuery,
  IPaginationQuery,
} from '@denis_bruns/base-database-service';
import { MyExpressionBuilder, MyExpression } from './MyExpressionBuilder';
import { MyQueryExecutor } from './MyQueryExecutor';

export class MyDatabaseService extends BaseDatabaseService<MyExpression, any> {
  constructor(
    tableName: string,
    private readonly mockData: any[]
  ) {
    super(
      tableName,
      'id', // primary key name
      new MyExpressionBuilder(),
      new MyQueryExecutor(mockData)
    );
  }

  protected async prepareQueryParameters(query: IGenericFilterQuery) {
    const { filters = [], pagination = {} } = query;
    const { limit, offset, page } = this.calculatePaginationValues(pagination as IPaginationQuery);

    // Build the expression using our custom builder
    const params = this.expressionBuilder.buildFilterExpression(filters);

    return {
      params,
      limit,
      offset,
      page,
      pagination
    };
  }

  protected processResults<T>(
    items: any[],
    limit: number,
    offset: number
  ): T[] {
    // Example: slice items for pagination
    return items.slice(offset, offset + limit) as T[];
  }

  protected handleError(error: any): void {
    console.error('Database error:', error);
  }
}

4. Use Your Derived Service

import { IGenericFilterQuery } from '@denis_bruns/web-core-ts';

async function example() {
  // Sample data to simulate a store
  const dataSource = [
    { id: '1', name: 'Item 1' },
    { id: '2', name: 'Item 2' },
    { id: '3', name: 'Item 3' },
  ];

  const dbService = new MyDatabaseService('my-table', dataSource);

  const query: IGenericFilterQuery = {
    filters: [{ field: 'name', operator: '=', value: 'Item 1' }],
    pagination: { page: 1, limit: 10 },
  };

  const results = await dbService.fetchWithFiltersAndPagination(query, null);
  console.log('Paginated and filtered results:', results);
}

Additional Utilities

validatePagination: Ensures page/limit/offset are integers.
validateValue: Checks for forbidden patterns ($where, $regex, etc.) to prevent potential NoSQL injection.
calculatePaginationValues: Converts page, limit, and optional offset to final integers used by your database queries.

Related Packages

@denis_bruns/web-core-ts

Foundational interfaces and types for building modular, testable web applications.
@denis_bruns/nosql-mongodb-service

Ready-to-use NoSQL data service built on MongoDB.
@denis_bruns/nosql-dynamodb-service

A DynamoDB-specific implementation leveraging expression builders and typed queries.