layer-data

Multi-data source data layer for apps.

Basics

Initialize a SQLite database

// Path of the database file
const db_path = 'data/my-data.db';

// Initialize database
const db = new SQLite(db_path);

// Retrieve a "Hello World"
const data = await db.queryData(`SELECT 'Hello World'`);

// Prints "Hello World"
console.log(data[0]);

Object-Relational Mapping

Aims to be not too complex, just useful enough.

Define Entity, Schema, Mapper and Repo

export interface PersonEntity{
    id: number;
    name: string;
}

export const PersonEntitySchema: SchemaOf<PersonEntity> = {
    properties:{
        "id": {type: "number"},
        "name": {type: "string"},
    },
    required: ["id", "name"]
};

export const PersonEntityMapper: EntityMapper<PersonEntity> = {
    table: "person",
    primaryKey: "id",
    autoIncrement: "id"
};

export class PersonRepo extends EntityRepository<PersonEntity>{
    constructor(readonly db: DataSource){
        super(db, PersonEntitySchema, PersonEntityMapper);
    }
}

Basic Use Cases

Initialize:

// Initialize DB
const db = new SQLite('my-data.db');

// Initialize Repo
const repo = new PersonRepo(db);

Insert an Entity

const person  = repo.insert({id: 0, name: "John Doe"});

// Prints 1, since id is auto-increment
console.log(person.id);

Retrieve an Entity

const person = repo.getOne(1);

// Prints "John Doe"
console.log(person.name);

Update an Entity

person.name = 'John Smith';

// Updates on DB
repo.update(person);

Delete an Entity

repo.delete(person);

const person = repo.getOne(1);

// person is undefined

Migrations Support

Migrations are loaded from a directory on a flat structure of .sql files.

Basic rules:

• Migrations must be .sql files
• Migrations need a version identifier
• Double underscore __ separates version from migration name
• Migrations should not change once applied
• Migrations are persisted in a database table called schema_migration
• It only takes one line to initialize the migrations support:

   migrationManager.makeSureMigrationsAreUpToDate();

Example directory:

/data
  V1__Base_Schema.sql
  V2__Add_Table_Product.sql
  V3__Add_Column_Price.sql

Typical Initialization:

 // Initialize DB
 const db = new SQLite('my-data.db');

// Path to folder where migrations are contained
schemaPath = 'data/migrations/sqlite';

// Initialize MigrationManager
MigrationManager mm = new MigrationManager(db, {schemaPath});

// Run migration manager
mm.makeSureMigrationsAreUpToDate();