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NestJS API CRUD Operation Using PostgreSQL Relational Database


NestJS API is a server-side framework that runs on NodeJS frameworks like Express. NestJS application has the ability to talk with both SQL and Non-SQL databases.

Here we will develop a sample NestJS API application that communicates with the PostgreSQL relational database.

NestJS Database Communication Flow:

The 'pg'(PostgreSQL NodeJS library) library was used for communicating with the PostgreSQL database. The 'typeorm'(NodeJS library) library is a framework used for querying the database or manipulating the database using the specified database library(in our case 'pg' node library). The 'typeorm' will be used for all database configurations also. The '@nestjs/typeorm'(NestJS ORM library) is an overlay or wrapper for the 'typeorm'(NodeJS library). By using '@nestjs/typeorm' it gives the advantage of Typescript compatibility and additional feature over 'typeorm'(NodeJS library). So while implementing NestJS application in max scenarios we will only use the '@nestjs/typeorm' library which will internally communicate with 'typeorm'(NodeJS library).

PostgreSQL Database Using ElephantSQL Cloud Service:

So for our application, we need to set up a PostgreSQL relational database. Here I'm going to set up a free cloud service PostgreSQL database provided by ElephantSQL for our demo purpose. It is a very easy setup, to do it takes 3-5minutes to setup, click here for steps to configure the ElephantSQL cloud service.

Create A Sample NestJS App:

Let's begin our sample by creating a NestJS application. Here we use NestJS CLI(command line interface) to create app.
Command To Install Nest CLI:

npm i -g @nestjs/cli
NestJS CLI Command To Create APP:

nest new your_project_name
By default NestJS application configured to run on portnumber '3000'. So execute the below command to start the application.
Commands To Start App:

npm run start
   or
npm run start:dev ---> runs application in watch mode prefered for development time
   or
npm run start:prod ---> production mode 

Npm Packages:

Install the following npm packages that are needed to accomplish our sample NestJS application.
Install NestJS Typeorm:

npm install --save @nestjs/typeorm
Install NodeJS Typeorm:

npm install --save typeorm
Install NodeJS PostgreSQL:

npm install --save pg

typeorm Decorators For Table Entities:

To make our typescript entity or model as table related entity, then we need to use decorators that are provided by the 'typeorm'(node js library).

@Entity() - This decorator is used to mark classes that will be an entity(table or document depends on database type). A database scheme will be created for all classes decorate with it, and the repository can be retrieved and used for it.

@PrimaryColumn() - This decorator is used to mark the property of an entity as a primary column of the table. It has the capability of the incremental integer value to save.

@Column() - This decorator is used to mark the property of class as the column of the table.

Create An Employee Table Entity:

In this sample, we are going to develop CRUD operations on the Employee table in the PostgreSQL relational database.

As a first step lets create a typescript Employee class that represents the database table.
src/Employee/employee.entity.ts:
import { Entity, PrimaryGeneratedColumn, Column } from 'typeorm';

@Entity()
export class Employee {
  @PrimaryColumn()
id: number; @Column() name: string; @Column() salary: number; @Column() age: number; }
  • (Line: 1) all required decorators are imported from the 'typeorm'(NodeJS library)
  • (Line: 3) typescript class Employee decorated with '@Entity()' decorator to make it as table class.
  • (Line: 5) 'id' property decorated with '@PrimaryColumn' decorator to make compatible with the primary column of the table.
  • @column() decorator was used on all other properties of the typescript class to represent the table columns.

TypeOrmModule Of @nestjs/typeorm:

TypeOrmModule of @nestjs/typerorm(NestJs library) will be used to configure database settings, register table entities, register injectable repositories of entity types, etc. TypeOrmModule implements static overloaded methods like:
  • forRoot() - this method takes configuration like database settings to set up communication between the NestJS application and the database. This method always registered in the parent or root module of the application like the 'app module'.
  • forFeature() - this method is similar to the forRoot() method but it will be registered for child modules of the 'appmodule'.
  • forRootAsync() - this async form forRoot() method.

Add PostgreSQL Configuration To AppModule:

To establish communication with the PostgreSQL database need to add configuration in TypeOrmModule at app.module.ts file to register globally.
src/app.module.ts:
import { TypeOrmModule } from '@nestjs/typeorm';
import { Employee } from './Employee/employee.entity';
// some code hidden for display purpose
@Module({
  imports: [
    TypeOrmModule.forRoot({
      type: 'postgres',
      host: 'lallah.db.elephantsql.com',
      port: 5432,
      username: '-----------',
      password: '-----------',
      database: '-----------',
      entities: [Employee],
    })
  ]
})
export class AppModule {}
  • (Line: 7) 'type' defines the database will be used since we are using the PostgreSQL database so we can pass the constant value of 'postgres'. 
  • (Line: 8) 'host' database server hosted
  • (Line: 9) the port number, '5432' is the default port number for the PostgreSQL database.
  • (Line: 10&11&12) database username, password, name of the database
  • (Line: 13) entities of the database need to register, it takes an array of entity types.
  • Click here for identifying PostgreSQL configurations

Pre-defined Repository Of typeorm:

The 'typeorm'(NodeJS library) provides Pre-defined 'Repository<TEntity>'. This pre-defined 'Repository' is supposed to work with our entity objects. It responsibilities are like 'find entities', 'insert', 'update', 'delete', etc.

InjectRepository Decorator From @nestjs/typeorm:

The '@nestjs/typeorm'(NestJS library) provides 'InjectRepository' decorator. This 'InjectRepository' decorator helps to inject the 'Repository<TEntity>' from 'typeorm'(NodeJS library) into the service files constructor of our application.

Create EmployeeService:

In general, all our logical code will be implemented in our 'service' files.
src/Employee/employee.service.ts:
import { Injectable } from '@nestjs/common';
import { Repository } from 'typeorm';
import { InjectRepository } from '@nestjs/typeorm';


@Injectable()
export class EmployeeService {
  constructor(@InjectRepository(Employee) private employeeRepo: Repository<Employee>) {}
}
  • (Line: 6) 'Injectable' decorator used on 'EmployeeService' to make it as an injectable service
  • (Line: 8) 'Repository<Employee>' injected into the service class with the help of '@InjectRepository()' decorator.

Add Fetch All Employee Logic:

Now in service using the repository, we are going to query the PostgreSQL relational database. Repository from 'typeorm'(NodeJS library) is built with a predefined query method which makes our logic simple and easy for database communication. Now here we will implement the method to fetch all our employee data.
src/Employee/employee.service.ts:
import { Employee } from './employee.entity';
// code hidden for display purpose
@Injectable()
export class EmployeeService {
   findAll(): Promise<Employee[]> {
    return this.employeeRepo.find();
  }
}
  • The 'find()' method from the repository which will take optional filter parameters to query against the database. If no filter parameters passed it return all the data from the database.
  • The 'find()' method returns a promise of an array of the entity type.

Create Employee Controller With Read Operation:

Now let's add the Employee controller for our sample application. Create an endpoint to read all the employees from the PostgreSQL relational database.
src/Employee/employee.controller.ts:
import { Controller, Get } from '@nestjs/common';
import {EmployeeService} from './employee.service';
import {Employee} from './employee.entity';

@Controller('employee')
export class EmployeeController {
    constructor(private readonly employeeService: EmployeeService){}

    @Get('all')
    async getAll():Promise<Employee[]>{
        return await this.employeeService.findAll();
    }
}
  • '@Controller()' decorator that makes class as Nest controller that can receive the inbound request and produce the response.
  • '@Get()' decorator is a route handler decorator. Routes Http Get request to the specified path.
  • (Line: 7) injected 'EmployeeService'
  • (Line: 9-12)Http method that executes read operation to fetch all the employee data.

Create An Employee Module:

In NestJS implementation each business logic will be developed as simple separate modules. These Modules acts entry point to register all configuration like 'controllers', 'services', 'entities', etc. So here we need to create an Employee module for our business.
src/Employee/employee.module.ts:
import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';

import { EmployeeController } from './employee.controller';
import { Employee } from './employee.entity';
import { EmployeeService } from './employee.service';

@Module({
  imports: [TypeOrmModule.forFeature([Employee])],
  providers: [EmployeeService],
  controllers: [EmployeeController],
})
export class EmployeeModule {}
  • 'TypeOrmModule.forFeature([Employee])' makes the 'Emplyee' entity schema available to 'Repository' from the 'typeorm'(NodeJS library) to query the database.
  • 'EmployeeService' registered to providers array to load the service for the Employee module.
  • 'EmployeeController' registered to controllers array to expose the routes.

Register Child Modules To AppModule:

Now to load or expose the child modules in an application we need to import those child modules in the app.module.ts file.
src/app.module.ts:
import { EmployeeModule } from './Employee/employee.module';

// code hidden for display purpose
@Module({
  imports: [
    EmployeeModule,
  ]
})
export class AppModule {}
Now start the application and access the newly created endpoint and output shows as below.

Create Operation:

Now we are going to implement a create operation to create new employees.
src/Employee/employee.service.ts:
create(newEmploye){
 this.employeeRepo.insert(newEmploye)
}
'insert()' method provided by the 'Repository' imported from 'typeorm'(NodeJS library). This method inserts a given entity. Executes fast and efficient Insert queries. Doesn't check if the entity exists in the database, so the query will fail if a duplicate entity tries to insert.

Now in the controller let's add a post-action method.
src/Employee/employee.controller.cs:
import { Controller, Get, Post, Body, HttpCode } from '@nestjs/common';

@Post('add')
@HttpCode(201)
createEmployee(@Body() newEmployee:any){
	this.employeeService.create(newEmployee);
}
  • '@Post()' request handler decorator. Routes Http Post request to the specified path.
  • '@HttpSatatusCode' request method decorator. Defines the Http response status code. Overrides default status code for the decorated request method. '201' status code stands for created successfully.
  • '@Body()' route handler parameter decorator. Extract the entire body object from the request object and populate the decorated parameter with the value of the body.



Update Operation:

Add the following code to update a record.
src/Employee/employee.service.ts:
update(employeetoUpdate){
    this.employeeRepo.update(employeetoUpdate.id,employeetoUpdate);
}
'update()' method from 'Repository' imported from 'typeorm'. This method is an overloaded method. It has the capability to do a partial update without effecting other column's data.
src/Employee/employee.controller.cs:
@Post('update')
@HttpCode(200)
updateEmployee(@Body() employeeToUpdate:any){
	this.employeeService.update(employeeToUpdate);
}


Delete Operation:

src/Employee/employee.service.ts:
delete(id){
  this.employeeRepo.delete(id);
}
'delete()' method of 'Repository' from 'typeorm'. Bypassing the primary key id is enough to remove the record from the database.
src/Employee/employee.controller.ts:
@Delete('delete/:id')
@HttpCode(200)
deleteEmployee(@Param('id') id){
	this.employeeService.delete(id);
}
  • '@Delete()' route handler decorator. Routes Http Delete requests to the specified path.
  • '@Param()' this decorator is to extract the data from the route.

Wrapping Up:

Hopefully, I think this article delivered some useful information on creating a sample of NestJS CRUD operations using the relational database PostgreSQL. I love to have your feedback, suggestions, and better techniques in the comment section below.

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