Base Data Sources and Type Safety in Xeno

Base Data Sources & Type Safety

In a Clean Architecture setup, the infrastructure layer is responsible for database communication.To maintain strict type safety with Drizzle ORM while avoiding union - type resolution conflicts between different SQL engines, Xeno provides specialized base classes: BasePostgresSqlDataSource and BaseSqliteSqlDataSource.

This guide explains how to implement domain contracts and choose the correct base data source according to your target database driver.

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Architecture Overview

A Data Source sits strictly within the Infrastructure Layer.It implements a persistence contract defined by the Domain layer(e.g., IUserDataSource) and uses Drizzle ORM via this.db to execute queries safely.

Depending on your database setup, you extend either:

• `BasePostgresSqlDataSource` for PostgreSQL(NodePgDatabase)
• `BaseSqliteSqlDataSource` for SQLite / libSQL(LibSQLDatabase)

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Implementation Guide

Step 1: Implement the Contract

Your data source class must implement the specific persistence contract expected by your repository.

Step 2: Extend the Appropriate Base Class

Pass your database schema to the generic base class. This automatically types this.db to your specific driver, giving you full autocompletion and compile - time safety without any manual casting.

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3. Code Example(UserDataSource)

Below is an example of a concrete implementation using PostgreSQL:

import {  } from '@xeno-js/core'
import type { IWriteDataSource, Optional, UserContext } from '@xeno-js/core'
import { AppError, and, Enumerable, eq, Guards } from '@xeno-js/core'
import { UserDto, users } from '../schemas/user.schema'
import type { DbSchema } from '../../../schema'
import { BasePostgresSqlDataSource } from './base-postgres-sql.datasource'

export class UserDataSource extends BasePostgresSqlDataSource<DbSchema> implements IWriteDataSource<UserDto> {

    public async findById(
        id: string | number,
        ctx: UserContext,
        signal: Optional<AbortSignal>
    ): Promise<Optional<UserDto>> {
        AppError.throwIfAborted(signal, 'UserDataSource.findById')

        const conditions = [eq(users.id, String(id))]
        if (Guards.isDefined(ctx.tenantId)) {
            conditions.push(eq(users.tenantId, ctx.tenantId))
        }

        // 'this.db' is fully typed as NodePgDatabase<DbSchema>
        const result = await this.db
            .select()
            .from(users)
            .where(and(...conditions))
            .limit(1)
            .execute()

        return Enumerable.firstOrDefault(result)
    }

    // Implement remaining methods (findAll, insert, update, delete, etc.)
}

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Summary of Base Classes

Database Engine	Base Class to Extend	Inferred Type for this.db
PostgreSQL	BasePostgresSqlDataSource<TSchema>	NodePgDatabase<TSchema>
SQLite / libSQL	BaseSqliteSqlDataSource<TSchema>	LibSQLDatabase<TSchema>

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