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Query Repository

In the CQRS architecture, the Query Repository is responsible for accessing and retrieving data from the database. It is used to perform read operations, ensuring that queries return the necessary data for processing.

Implementation​

To retrieve the queried entities from the database, we use a Query Repository. This repository handles the interaction with the database, abstracting away the complexities of data access.

An implementation of a Query Repository can be found at: Task/src/useCases/read/ActiveTaskOverview/infrastructure/ActiveTaskOverviewRepository.ts.

import { OverwriteProtectionBody } from "@codebricks/codebricks-framework";
import { ActiveTaskOverviewEntity } from "shared/application/readmodels/ActiveTaskOverviewEntity";
import { AppDataSource } from "shared/infrastructure/persistence/AppDataSource";

export class ActiveTaskOverviewRepository {
    @OverwriteProtectionBody(false)
    async getAll(): Promise<ActiveTaskOverviewEntity[]> {
        return await AppDataSource.manager.find(ActiveTaskOverviewEntity, {
            where: {
            }
        });
    }
}

Code Explanation​

  • ActiveTaskOverviewRepository Class: This class acts as the Query Repository for the ActiveTaskOverviewEntity. It is responsible for fetching data from the database.

  • getAll Method:

    • This method retrieves all instances of ActiveTaskOverviewEntity from the database.
    • It uses TypeORM’s find method to perform the query. TypeORM is an ORM (Object-Relational Mapping) library that simplifies database interactions in TypeScript applications.

Key Concepts​

  • ORM (Object-Relational Mapping): A programming technique for converting data between incompatible type systems in object-oriented programming languages. TypeORM is used to map TypeScript classes to database tables.

  • TypeORM Notation: The method find is part of TypeORM’s API for querying the database. It allows specifying conditions to fetch records from the database.

Best Practices​

  • Repository Pattern: Use repositories to encapsulate data access logic and isolate it from the rest of the application. This pattern helps in managing data retrieval and manipulation efficiently.

  • Error Handling: Implement proper error handling in your repository methods to manage database errors and provide meaningful feedback.