TypeORM Basics — Series 3

Preview — 3 of 10 questions

What is the practical difference?

javascript

@PrimaryGeneratedColumn('uuid') id: string;      // (1)
@PrimaryGeneratedColumn() id: number;            // (2)

AForm (1) is faster to index because the values are shorter

BForm (2) is required whenever the table has relations

CForm (2) produces a sequential integer — compact and index-friendly, but it leaks how many rows exist and lets anyone guess neighbouring ids — while form (1) produces an unguessable identifier that can be generated by the application before the row is written, at the cost of a wider index

DForm (1) guarantees uniqueness only within one table, unlike form (2)

What does the argument do?

javascript

@Entity('cats')
export class Cat { /* ... */ }

AIt sets the table name explicitly, instead of letting the naming strategy derive one from the class name

BIt names the entity for the repository token, without affecting the table

CIt creates a database schema called cats

DIt registers an alias used only in QueryBuilder expressions

What column does this create by default, and how would it become created_by_user_id?

javascript

@Column() createdByUserId: string;

Acreated_by_user_id, since snake_case is TypeORM's default

BCREATEDBYUSERID, because identifiers are upper-cased

CIt cannot be changed without renaming the property

DcreatedByUserId by default — the property name is used verbatim — and a project-wide SnakeNamingStrategy (or an explicit @Column({ name: 'created_by_user_id' })) is what produces the snake_case form

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