Let's say we are constructing our very first entities for a new web application. There is an entity for users:
@Entity()
export class User {
@PrimaryGeneratedColumn()
id: number;
@Column()
username: string;
@Column()
password: string;
@OneToOne(() => Author)
author: Author;
Users can be Authors after registration. So there's a one-to-one relationship between users and authors table. Let's say we have another table called books, an author can have multiple books.
export class Author {
@PrimaryGeneratedColumn()
id: number;
@Column()
Name: string;
@OneToMany(() => Book, (Book) => Book.Author)
Book: Book[];
@OneToOne(() => User)
@JoinColumn()
User: User;
Here is a sample entity for Books repository:
export class Book {
@PrimaryGeneratedColumn()
id: number;
@Column()
Name: string;
@Column()
ISIN: string;
@OneToOne(() => Author)
@JoinColumn()
Author: Author;
The question is, when we migrated these entities and built our very first/clean database, how can we insert the data via calling API? A sample service for API Post method:
@Injectable()
export class BookService {
constructor(
@InjectRepository(Book)
private BookRepository: Repository<Book>,
) {}
async create(createBookDto: CreateBookDto) {
await this.BookRepository.insert(createBookDto);
}
}
And the Controller:
@Controller('books')
export class BookController {
constructor(private readonly BookService: BookService) {}
@Post('/Book')
create(@Body() createBookDto: CreateBookDto) {
return this.BookService.create(createBookDto);
}
}
The problem here is that when I want to create a new book by POSTing data to the API route, it needs the Author to be defined. So how can I post existing user-books-author data into the database via this service?
The best option I think of is to create a new instance of the classes, get the data from request @Body and assign it to the objects of the class then save it to the database.
But I think it's not a good solution, as it's very preferred to use repositories instead of object-class type.
I think you do a mistake in your entity definition. There is OneToMany relation between Author to Book.
Modify your book entity like this
export class Book {
@PrimaryGeneratedColumn()
id: number;
@Column()
Name: string;
@Column()
ISIN: string;
@ManyToOne(() => Author, author=> author.book, { nullable: true })
@JoinColumn()
Author: Author;
{ nullable: true } this will allow you to save your book data without having an author.
Modify your service to save the book information
public async create(createBookDTO: CreateBookDTO) {
try {
if (
createBookDTO.hasOwnProperty('author') &&
createTaskDTO.author
) {
const author = await this.connection.manager.findOne(Author, {
where: {
id: createBookDTO.author,
},
});
if (author) {
createBookDTO.author = author;
} else {
throw new NotAcceptableException('Author not found');
}
}
return await this.bookRepo.save(createBookDTO);
} catch (err) {
throw new HttpException(err, err.status || HttpStatus.BAD_REQUEST);
}
}