Topic
Definition
A TypeORM entity is a TypeScript class decorated with @Entity whose properties, marked with column decorators such as @Column, @PrimaryGeneratedColumn, @CreateDateColumn, and @UpdateDateColumn, map to the columns of a single database table.
In simpler words
An entity is the SQL table from earlier, written as a typed class so the rest of the app can read and write rows as objects instead of raw SQL strings.
User and Ticket in this repo are the entities behind every users/tickets row you have already seen in raw SQL.
Definition
@Entity({ name: ... }) associates a class with a specific table name, and @Column (with options) associates a property with a specific column, its type, and its constraints.
In simpler words
Read an entity top-to-bottom and you are reading the same information as the CREATE TABLE statement, just in TypeScript.
User maps to the users table; every @Column here corresponds 1:1 to a column you already saw in InitSchema.
Column options mirror SQL constraints: unique, nullable, default, length, and an explicit type when it differs from the TypeScript type.
@Entity({ name: 'users' })
export class User {
@PrimaryGeneratedColumn('uuid')
id!: string;
@Column({ unique: true })
email!: string;
@Column({ name: 'password_hash' })
passwordHash!: string;
@Column({ type: 'varchar', length: 20, default: 'member' })
role!: UserRole;
}@Column({ name: 'password_hash' }) maps a camelCase property to a snake_case column — property and column names do not have to match.
Definition
@PrimaryGeneratedColumn generates a primary key value automatically on insert, and @CreateDateColumn / @UpdateDateColumn automatically populate creation and last-modified timestamps without application code setting them.
In simpler words
These decorators exist so nobody has to remember to set id, created_at, or updated_at by hand on every insert or update.
@PrimaryGeneratedColumn('uuid') tells TypeORM (and the migration it generates) to default the column to a generated UUID, matching gen_random_uuid() in SQL.
@UpdateDateColumn refreshes its value on every save() — this is how Ticket.updatedAt stays accurate without manual bookkeeping.
@Entity({ name: 'tickets' })
export class Ticket {
@PrimaryGeneratedColumn('uuid')
id!: string;
@Column({ length: 200 })
title!: string;
@Column({ type: 'text', nullable: true })
description!: string | null;
@CreateDateColumn({ name: 'created_at', type: 'timestamptz' })
createdAt!: Date;
@UpdateDateColumn({ name: 'updated_at', type: 'timestamptz' })
updatedAt!: Date;
}description is explicitly nullable — its TypeScript type says so too (string | null).
Definition
Column decorator options (unique, nullable, default, length, type) directly control the constraints and type that TypeORM will generate in a migration for that column.
In simpler words
Every option you set here should have a reason traceable to a real business rule, the same discipline as choosing raw SQL types and constraints.
unique: true on email is exactly UNIQUE ("email") in SQL — TypeORM will name the constraint and generate it in a migration.
nullable: true is the TypeScript-side way of omitting NOT NULL for a column, as seen on Ticket.description and Ticket.assigneeId.
@Column({ name: 'assignee_id', type: 'uuid', nullable: true })
assigneeId!: string | null;nullable: true here matches the SQL column having no NOT NULL — an unassigned ticket is valid.
Test
At least 10 questions — mix of concept, syntax, practical, and logic. Score ≥ 80% (enforced by the API) to save progress.
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10 questions · concept 3 · syntax 2 · practical 3 · logic 2