Entity is a class that maps to a database table, or to a collection when using MongoDB. In the context of NestJS, which often pairs with Object-Relational Mapping tools like TypeORM, an entity functions as the data model for the application, interfacing directly with the database schema. This exemplifies the software engineering principle of data source abstraction, allowing for easier swapping of databases or migration. As a best practice, encapsulating database interactions within repository classes streamlines code maintenance and enhances testability.  

import { Column, Entity, PrimaryGeneratedColumn } from "typeorm";

@Entity("songs")
export class Song {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  title: string;

  @Column("varchar", { array: true })
  artists: string[];

  @Column({ type: "date" })
  releasedDate: Date;

  @Column({ type: "time" })
  duration: Date;

  @Column({ type: "text" })
  lyrics: string;
}

 serves to automatically increment the primary key, a feature that may be specified either here or directly within the database. 

 defines a column, allowing specification of various data types such as date, varchar, and time. This column definition offers precise mapping, crucial for efficient data querying and comprehensive schema definition.  

@Column('varchar', { array: true })
artists: string[];

An array of artists exists, serving as a data structure to hold multiple artist entities. To create this array field in a Postgres database, metadata is added to the 

 decorator in the NestJS application. As a best practice, strongly typing this array—for instance, as 

—can improve code maintainability and reduce potential runtime errors. In addition, leveraging Postgres' native array data type within the 

 decorator provides optimizations for array operations and queries.

@Column({ type: 'date' })
releasedDate: Date;

 type is specified for the release date, ensuring that no time-related properties are added to the 

 field. In NestJS, using class-validator's 

 property would further enforce type safety and validation, adhering to best practices for robust, production-ready code.

---
title: Create an Entity
privateVideoUrl: https://fullstack.wistia.com/medias/7nasttyqmk
isPublicLesson: true
---

## Create an Entity

Entity is a class that maps to a database table, or to a collection when using MongoDB. In the context of NestJS, which often pairs with Object-Relational Mapping tools like TypeORM, an entity functions as the data model for the application, interfacing directly with the database schema. This exemplifies the software engineering principle of data source abstraction, allowing for easier swapping of databases or migration. As a best practice, encapsulating database interactions within repository classes streamlines code maintenance and enhances testability.  

```ts
import { Column, Entity, PrimaryGeneratedColumn } from "typeorm";

@Entity("songs")
export class Song {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  title: string;

  @Column("varchar", { array: true })
  artists: string[];

  @Column({ type: "date" })
  releasedDate: Date;

  @Column({ type: "time" })
  duration: Date;

  @Column({ type: "text" })
  lyrics: string;
}
```

In the class Entity: `@Entity('songs')` indicates that `songs` is the name of the database table. `@PrimaryGeneratedColumn()` serves to automatically increment the primary key, a feature that may be specified either here or directly within the database. `@Column()` defines a column, allowing specification of various data types such as date, varchar, and time. This column definition offers precise mapping, crucial for efficient data querying and comprehensive schema definition.  

```ts
@Column('varchar', { array: true })
artists: string[];
```

An array of artists exists, serving as a data structure to hold multiple artist entities. To create this array field in a Postgres database, metadata is added to the `@Column` decorator in the NestJS application. As a best practice, strongly typing this array—for instance, as `string[]`—can improve code maintainability and reduce potential runtime errors. In addition, leveraging Postgres' native array data type within the `@Column` decorator provides optimizations for array operations and queries.

Haider Malik

Create an Entity

In this lesson, I'm going to teach you how to create an entity.

Entity is a class that maps to database table.

You can create entity by defining a new class and mark it with an entity

And inside the metadata, you can provide the name of the table.

In our case, I'm going to provide the songs table name, an ID which is the

And we have the title, I use the column decorator.

For artist array, postgres also supports a data type.

You have to provide the column and I'm using the var character.

You have to say this column is an array type.

You have to specify the array should be true.

And we have a release date property or release date field in the database table

I'm specifying the column decorator and we are saying this, the type of this

You can say we have the duration, I specified the date, data type.

In the postgres, you can define the time.

I don't want to save extra date field here.

I only need time properties, time related metadata.

And lyrics, lyrics could be the long text.

If you want a long, if you want to store a string with long content or long

And it is songs which is the name of the table.

And you can say I have specified the description for each field.

When you will create the entity, you also need to update the lyrics in the

We did not add lyrics property in the previous videos.

And finally we need to register the entity to the app module.

Songs.entity or song, whatever you want to call.

The file character and the type should be array.

Now it should create the songs table for us.

You are going to learn how to perform CRUD operation.

Update, delete, find one, find all and create.

This time we are going to fetch and save data to the database.

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