Migrations in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the migrations module in NestJS.

NestJS

import { [1] } from '@nestjs/typeorm';

Drag options to blanks, or click blank then click option'

ATypeOrmModule

BMigrationService

CMigrationsModule

DMigrationModule

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent module like MigrationService.

Confusing MigrationModule with TypeOrmModule.

The TypeOrmModule is imported to use migrations with NestJS and TypeORM.

2fill in blank

medium

Complete the code to configure migrations in the TypeOrmModule.

NestJS

TypeOrmModule.forRoot({
  migrations: ["[1]"],
  migrationsRun: true,
});

Drag options to blanks, or click blank then click option'

Amigrations/*.js

Bmigrations/*.ts

CMigrationFiles

DMigrationScripts

Attempts:

3 left

💡 Hint

Common Mistakes

Using TypeScript files path instead of JavaScript.

Using undefined variables like MigrationFiles.

The migrations array expects the path to compiled JavaScript migration files, usually migrations/*.js.

3fill in blank

hard

Fix the error in the migration class name to follow NestJS migration conventions.

NestJS

export class [1] implements MigrationInterface {
  async up(queryRunner: QueryRunner): Promise<void> {
    // migration code
  }
  async down(queryRunner: QueryRunner): Promise<void> {
    // revert code
  }
}

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Acreateusertable

BcreateUserTable

Ccreate_user_table

DCreateUserTable

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase or snake_case for class names.

Starting class names with lowercase letters.

Migration class names should be PascalCase starting with a capital letter, like CreateUserTable.

4fill in blank

hard

Fill both blanks to correctly run migrations using the CLI command.

NestJS

npm run [1] -- [2]

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Atypeorm

Bmigration:run

Cstart

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' or 'build' instead of 'migration:run'.

Using wrong npm script names.

The command npm run typeorm -- migration:run runs the migrations using the TypeORM CLI.

5fill in blank

hard

Fill all three blanks to create a migration file with the correct CLI command and naming.

NestJS

npm run [1] -- [2] [3]

Drag options to blanks, or click blank then click option'

Atypeorm

Bmigration:create

CAddProductsTable

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' instead of 'typeorm' for the npm script.

Using 'migration:run' instead of 'migration:create'.

Using lowercase or snake_case for migration names.

The command npm run typeorm -- migration:create AddProductsTable creates a new migration file named AddProductsTable.

Practice

1. What is the main purpose of migrations in a NestJS project using TypeORM?

easy

A. To handle HTTP requests and responses

B. To safely update the database schema step-by-step

C. To write business logic for the application

D. To manage user authentication

Solution

1. Step 1: Understand what migrations do

   Migrations help change the database structure safely without losing data.

2. Step 2: Identify the correct purpose in NestJS context

   They are not for business logic or HTTP handling but for database schema updates.

3. Final Answer:

   To safely update the database schema step-by-step -> Option B

4. Quick Check:

   Migrations = safe database updates [OK]

Hint: Migrations change database structure safely [OK]

Common Mistakes:

• Confusing migrations with business logic
• Thinking migrations handle HTTP requests
• Assuming migrations manage authentication

2. Which command correctly runs all pending migrations in a NestJS project using TypeORM?

easy

A. npx typeorm migration:create

B. npx typeorm migration:revert

C. npx typeorm migration:generate

D. npx typeorm migration:run

Solution

1. Step 1: Recall commands for migrations

   migration:run applies pending migrations to the database.

2. Step 2: Differentiate from other commands

   migration:create creates a new migration file, migration:generate generates migration from schema changes, and migration:revert undoes the last migration.

3. Final Answer:

   npx typeorm migration:run -> Option D

4. Quick Check:

   Run migrations = migration:run [OK]

Hint: Run migrations with migration:run command [OK]

Common Mistakes:

• Using migration:create to run migrations
• Confusing migration:generate with migration:run
• Using migration:revert to apply migrations

3. Given this migration class, what will happen when up() is run?

export class AddAgeColumn1678901234567 {
  async up(queryRunner) {
    await queryRunner.query(`ALTER TABLE users ADD COLUMN age int`);
  }
  async down(queryRunner) {
    await queryRunner.query(`ALTER TABLE users DROP COLUMN age`);
  }
}

medium

A. Creates a new table called 'age'

B. Removes the 'age' column from the 'users' table

C. Adds a new integer column 'age' to the 'users' table

D. Throws a syntax error because of missing semicolons

Solution

1. Step 1: Analyze the up() method

   The up() method runs SQL to add a column named 'age' of type integer to the 'users' table.

2. Step 2: Understand the effect of the query

   This modifies the existing 'users' table by adding the new column; it does not remove columns or create new tables.

3. Final Answer:

   Adds a new integer column 'age' to the 'users' table -> Option C

4. Quick Check:

   up() adds column 'age' [OK]

Hint: up() applies changes like adding columns [OK]

Common Mistakes:

• Confusing up() with down() method
• Thinking it creates a new table
• Assuming syntax error due to semicolons

4. You wrote this migration but get an error when running npx typeorm migration:run. What is the likely problem?

export class RemoveEmailColumn1678901234568 {
  async up(queryRunner) {
    await queryRunner.query(`ALTER TABLE users DROP email`);
  }
  async down(queryRunner) {
    await queryRunner.query(`ALTER TABLE users ADD email varchar(255)`);
  }
}

medium

A. The SQL syntax for dropping a column is incorrect

B. The migration class name is invalid

C. Missing async keyword in down() method

D. The migration file is not saved

Solution

1. Step 1: Check the SQL in up() method

   The query ALTER TABLE users DROP email is incorrect SQL syntax for dropping a column.

2. Step 2: Correct SQL syntax for dropping a column

   The correct syntax is ALTER TABLE users DROP COLUMN email. Missing 'COLUMN' causes the error.

3. Final Answer:

   The SQL syntax for dropping a column is incorrect -> Option A

4. Quick Check:

   DROP COLUMN keyword required in SQL [OK]

Hint: Use DROP COLUMN to remove columns in SQL [OK]

Common Mistakes:

• Omitting COLUMN keyword in DROP statement
• Assuming class name causes error
• Forgetting async keyword (not the cause here)

5. You want to create a migration that renames a column 'username' to 'user_name' in the 'accounts' table and can be reverted. Which up() and down() methods are correct?

hard

A. async up(queryRunner) {
await queryRunner.query(`ALTER TABLE accounts RENAME COLUMN username TO user_name`);
}
async down(queryRunner) {
await queryRunner.query(`ALTER TABLE accounts RENAME COLUMN user_name TO username`);
}

B. async up(queryRunner) {
await queryRunner.query(`ALTER TABLE accounts CHANGE username user_name varchar(255)`);
}
async down(queryRunner) {
await queryRunner.query(`ALTER TABLE accounts CHANGE user_name username varchar(255)`);
}

C. async up(queryRunner) {
await queryRunner.query(`ALTER TABLE accounts DROP COLUMN username`);
await queryRunner.query(`ALTER TABLE accounts ADD COLUMN user_name varchar(255)`);
}
async down(queryRunner) {
await queryRunner.query(`ALTER TABLE accounts DROP COLUMN user_name`);
await queryRunner.query(`ALTER TABLE accounts ADD COLUMN username varchar(255)`);
}

D. async up(queryRunner) {
await queryRunner.query(`RENAME COLUMN username TO user_name`);
}
async down(queryRunner) {
await queryRunner.query(`RENAME COLUMN user_name TO username`);
}

Solution

1. Step 1: Identify correct SQL syntax for renaming columns

   The standard SQL syntax supported by many databases is ALTER TABLE table_name RENAME COLUMN old_name TO new_name.

2. Step 2: Check each option's SQL correctness and revert logic

   async up(queryRunner) {
     await queryRunner.query(`ALTER TABLE accounts RENAME COLUMN username TO user_name`);
   }
   async down(queryRunner) {
     await queryRunner.query(`ALTER TABLE accounts RENAME COLUMN user_name TO username`);
   }

   uses correct syntax for both up() and down() to rename and revert the column name.

   async up(queryRunner) {
     await queryRunner.query(`ALTER TABLE accounts CHANGE username user_name varchar(255)`);
   }
   async down(queryRunner) {
     await queryRunner.query(`ALTER TABLE accounts CHANGE user_name username varchar(255)`);
   }

   uses MySQL-specific CHANGE syntax which may not be portable.

   async up(queryRunner) {
     await queryRunner.query(`ALTER TABLE accounts DROP COLUMN username`);
     await queryRunner.query(`ALTER TABLE accounts ADD COLUMN user_name varchar(255)`);
   }
   async down(queryRunner) {
     await queryRunner.query(`ALTER TABLE accounts DROP COLUMN user_name`);
     await queryRunner.query(`ALTER TABLE accounts ADD COLUMN username varchar(255)`);
   }

   drops and adds columns, losing data.

   async up(queryRunner) {
     await queryRunner.query(`RENAME COLUMN username TO user_name`);
   }
   async down(queryRunner) {
     await queryRunner.query(`RENAME COLUMN user_name TO username`);
   }

   misses the table name in the query, causing error.

3. Final Answer:

   ALTER TABLE accounts RENAME COLUMN username TO user_name -> Option A

4. Quick Check:

   Rename column with ALTER TABLE RENAME COLUMN [OK]

Hint: Use ALTER TABLE RENAME COLUMN for renaming columns [OK]

Common Mistakes:

• Dropping and adding columns instead of renaming
• Omitting table name in ALTER TABLE
• Using database-specific syntax without checking compatibility