mydal

A simple JavaScript data access layer and table gateway implementation for MySQL.

By Joe Fallon

MyDAL has the following features:

• Promise support.
• Full suite of unit tests.
• It can be integrated into any existing project.
• Can be fully understood in just a few moments.
• The library implements the data mapper design patter (a.k.a. table gateway).
• The mysql npm package is used for all data access.
• Connection pooling is used by default.
• Written in TypeScript.

Installation

The easiest way to install MyDAL is with npm.

npm install mydal --save

Usage

There are two main classes that are used to represent all of the relationships within the database.

TableGateway
JoinTableGateway

Additionally, there is a factory called ConnectionPoolFactory for creating MySQL connection pools.

public static create(poolConfig: PoolConfig): Pool;

Entities

An entity represents a single row within a database. Another name for this type of object is data transfer object (DTO). Here is an example entity class for a row in a products table.

export class Product {
    public id:          number;
    public name:        string;
    public description: string;
    public price:       number;
    public created:     string;
    public updated:     string;

    public constructor() {
        this.created     = '';
        this.description = null;
        this.id          = 0;
        this.name        = '';
        this.price       = 0;
        this.updated     = '';
    }
}

TableGateway

Both of these classes are designed to be wrapped by classes that you create. The classes that you create can selectively expose the functionality provided.

The TableGateway class is designed to access all tables in the database that are not join (or associative) tables.

At a minimum, a class accessed by the TableGateway needs a primary key. The name of the primary key will default to id if one is not provided.

Optionally, two additional columns are provided for created and updated timestamps. The name of those to columns is configurable by you.

The TableGateway provides the following constructor:

// If no primary key is supplied, then "id" is assumed.
constructor(connectionPool: Pool, tableName: string, primaryKey = 'id');

The TableGateway provides the following promise style data access and modification methods:

// Returns the inserted row with the inserted primary key (e.g. id) added.
createRow(row: any): Promise<any>;

retrieveRow(id: number): Promise<any>;

updateRow(row: any): Promise<number>;

deleteRow(id: number): Promise<number>;

retrieveRows(fieldName: string, fieldValue: any): Promise<any[] | null>;

retrieveRowsByIds(ids: number[]): Promise<any[]>;

retrieveRowsByIsNull(fieldName: string): Promise<any[]>;

retrieveRowsByNotEqual(fieldName: string, fieldValue: any): Promise<any[]>;

setFieldNullWhere(fieldName: string, fieldValue: any): Promise<number>;

deleteRowsBy(fieldName: string, fieldValue: any): Promise<number>;

countRowsByValue(fieldName: string, fieldValue: any): Promise<number>;

The the following methods are used to set the optional created and updated timestamp columns names:

setCreatedColumnName(value: string): void;
setUpdatedColumnName(value: string): void;

Example Products Table Schema

Name        Type            Options
----------- --------------- ---------------------------
id          interger        non-null, autoincrement, pk
name        string          non-null
description string          nullable
price       decimal(10,2)   non-null
created     string          non-null
updated     string          non-null

Example ProductsGateway

import {Pool} from "mysql";

import {TableGateway} from "../../src/TableGateway";
import { Product } from '../entities/Product';

export class ProductsGateway {
    private static readonly TABLE_NAME = 'products';

    private readonly _tableGateway: TableGateway;

    constructor(connectionPool: Pool) {
        this._tableGateway = new TableGateway(connectionPool, ProductsGateway.TABLE_NAME);
        this._tableGateway.setCreatedColumnName('created');
        this._tableGateway.setUpdatedColumnName('updated');
    }

    /**
     * @returns The inserted Product.
     */
    public async createRow(product: Product): Promise<Product> {
        return this._tableGateway.createRow(product);
    }

    /**
     * @returns Retrieves the row with the given id if found, null otherwise.
     */
    public async retrieveRow(id: number): Promise<Product> {
        return this._tableGateway.retrieveRow(id);
    }

    /**
     * @returns Returns the number of affected rows (0 or 1).
     */
    public async updateRow(product: Product): Promise<number> {
        return this._tableGateway.updateRow(product);
    }

    /**
     * @returns Returns the number of affected rows (0 or 1).
     */
    public async deleteRow(id: number): Promise<number> {
        return this._tableGateway.deleteRow(id);
    }

    /**
     * @returns Returns an array of products.
     */
    public async retrieveByDescription(description: string): Promise<Product[]> {
        return this._tableGateway.retrieveRows('description', description);
    }

    /**
     * @returns Returns an array of Products.
     */
    public async retrieveByIds(ids: number[]): Promise<Product[]> {
        return this._tableGateway.retrieveRowsByIds(ids);
    }

    /**
     * @returns Returns an array of Products.
     */
    public async retrieveByNullDescription(): Promise<Product[]> {
        return this._tableGateway.retrieveRowsByIsNull('description');
    }

    /**
     * @returns Returns an array of Products.
     */
    public async retrieveByDescriptionNotEqual(description: string): Promise<Product[]> {
        return this._tableGateway.retrieveRowsByNotEqual('description', description);
    }

    /**
     * @returns Returns the number of affected rows.
     */
    public async setDescriptionNullWhereNameIs(value: string): Promise<number> {
        return this._tableGateway.setFieldNullWhere('description', value);
    }

    /**
     * @returns Returns the number of affected rows.
     */
    public async deleteWhereNameIs(name: string): Promise<number> {
        return this._tableGateway.deleteRowsBy('name', name);
    }

    /**
     * @returns Returns the count.
     */
    public async countProductsByName(name: string): Promise<number> {
        return this._tableGateway.countRowsByValue('name', name);
    }
}

It is also possible to forgo data mappers and return the results directly.

JoinTableGateway

The JoinTableGateway is used to manage access to an associative table that represents a many-to-many relationship.

As a review, a join table must consist of two fields, at a minimum. Each field is a foreign-key to another table. Optionally, a column with a timestamp to represent the time created is provided as well. It is assumed that the combination of the two foreign key fields is unique.

Example JoinTableGateway

import {Pool} from "mysql";
import {JoinTableGateway} from "../../src/JoinTableGateway";

export class OrdersProductsGateway {
    private readonly tableName = 'orders_products';
    private readonly id1Name   = 'table1_id';
    private readonly id2Name   = 'table2_id';

    private joinTableGateway: JoinTableGateway;

    constructor(connectionPool: Pool) {
        let table = this.tableName;
        let id1   = this.id1Name;
        let id2   = this.id2Name;
        this.joinTableGateway = new JoinTableGateway(connectionPool, table, id1, id2);
        this.joinTableGateway.setCreatedColumnName('created');
    }

    public createRow(id1: number, id2: number): Promise<boolean> {
        return this.joinTableGateway.createRow(id1, id2);
    }

    public retrieveRow(id1: number, id2: number): Promise<any> {
        return this.joinTableGateway.retrieveRow(id1, id2);
    }

    public deleteRow(id1: number, id2: number): Promise<number> {
        return this.joinTableGateway.deleteRow(id1, id2);
    }

    public retrieveByTable1Id(id1: number): Promise<any[]> {
        return this.joinTableGateway.retrieveById('table1_id', id1);
    }

    public deleteByTable1Id(id1: number): Promise<number> {
        return this.joinTableGateway.deleteById('table1_id', id1);
    }
}