Knex as query builder alternative in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize Knex with a SQLite3 client.

Express

const knex = require('knex')({ client: '[1]', connection: { filename: './data.db' } });

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

Amysql

Boracle

Cpg

Dsqlite3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'mysql' or 'pg' when the connection is a file path.

Forgetting to specify the client.

Knex uses the client option to specify the database type. For SQLite3, use sqlite3.

2fill in blank

medium

Complete the code to select all rows from the 'users' table using Knex.

Express

knex('[1]').select('*').then(rows => console.log(rows));

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

Ausers

Borders

Citems

Dproducts

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong table name like 'items' or 'orders'.

Forgetting to call select('*').

The table name to query is 'users'.

3fill in blank

hard

Fix the error in the Knex query to insert a new user with name 'Alice'.

Express

knex('[1]').insert({ name: 'Alice' }).then(() => console.log('Inserted'));

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

Auser

Buser_table

Cusers

Daccounts

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular 'user' instead of 'users'.

Using unrelated table names.

The correct table name is 'users' for inserting user data.

4fill in blank

hard

Fill both blanks to update the email of user with id 5 to '[e-mail]'.

Express

knex('[1]').where('[2]', 5).update({ email: '[e-mail]' }).then(() => console.log('Updated'));

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

Ausers

Bid

Cemail

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong table names like 'email' or 'username' as table.

Filtering by 'email' instead of 'id'.

The table is 'users' and the column to filter by is 'id'.

5fill in blank

hard

Fill all three blanks to delete users older than 30 from the 'users' table.

Express

knex('[1]').where('[2]', '[3]', 30).del().then(() => console.log('Deleted'));

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

Ausers

Bage

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong table names.

Using '<' instead of '>' for age comparison.

We delete from 'users' where 'age' is greater than 30.

Practice

1. What is the main advantage of using Knex as a query builder in an Express app?

easy

A. It allows writing database queries using JavaScript instead of raw SQL.

B. It automatically creates database tables without any code.

C. It replaces Express middleware for handling requests.

D. It compiles JavaScript into SQL code for faster execution.

Solution

1. Step 1: Understand Knex's purpose

   Knex is designed to let developers write database queries in JavaScript instead of SQL.

2. Step 2: Compare options

   Options B, C, and D describe features Knex does not provide. It does not create tables automatically, replace Express middleware, or compile JS into SQL.

3. Final Answer:

   It allows writing database queries using JavaScript instead of raw SQL. -> Option A

4. Quick Check:

   Knex = JS query builder [OK]

Hint: Knex lets you write queries in JS, not raw SQL [OK]

Common Mistakes:

• Thinking Knex creates tables automatically
• Confusing Knex with Express middleware
• Believing Knex compiles JS to SQL code

2. Which of the following is the correct way to select all rows from a table named users using Knex?

easy

A. knex.tables('users').select('*')

B. knex.from('users').selects()

C. knex.query('SELECT * FROM users')

D. knex.select('*').from('users')

Solution

1. Step 1: Review Knex select syntax

   The common pattern is knex.select('*').from('tableName') to get all rows.

2. Step 2: Check each option

   knex.select('*').from('users') matches the correct syntax. knex.from('users').selects() uses invalid selects() method. knex.tables('users').select('*') uses knex.tables which is not standard Knex syntax. knex.query('SELECT * FROM users') uses raw SQL string which is not the Knex query builder method.

3. Final Answer:

   knex.select('*').from('users') -> Option D

4. Quick Check:

   Correct select syntax = knex.select('*').from('users') [OK]

Hint: Use knex.select('*').from('table') to get all rows [OK]

Common Mistakes:

• Using knex.tables() instead of knex.select().from()
• Using selects() instead of select()
• Trying to pass raw SQL string to knex

3. What will the following Knex query return?

knex('products').where('price', '>', 100).select('id', 'name')

medium

A. All products with price less than or equal to 100, showing id and name.

B. All products with price greater than 100, showing all columns.

C. All products with price greater than 100, showing id and name.

D. Syntax error due to incorrect method chaining.

Solution

1. Step 1: Analyze the where clause

   The query filters products where price is greater than 100.

2. Step 2: Analyze the select clause

   It selects only the 'id' and 'name' columns to return.

3. Final Answer:

   All products with price greater than 100, showing id and name. -> Option C

4. Quick Check:

   where('price', '>', 100) + select('id', 'name') = All products with price greater than 100, showing id and name. [OK]

Hint: where filters rows; select chooses columns [OK]

Common Mistakes:

• Confusing > with < in where clause
• Assuming all columns are returned
• Thinking method chaining causes syntax error

4. Identify the error in this Knex query:

knex('orders').where('status' = 'pending').select()

medium

A. Missing table name in knex call.

B. Using '=' instead of ',' inside where method.

C. select() requires column names as arguments.

D. where method cannot be chained after knex call.

Solution

1. Step 1: Check where method syntax

   The where method expects arguments separated by commas, e.g., where('status', 'pending').

2. Step 2: Identify the error

   The query uses '=' inside where which is invalid syntax in JavaScript function calls.

3. Final Answer:

   Using '=' instead of ',' inside where method. -> Option B

4. Quick Check:

   where('status' = 'pending') is invalid [OK]

Hint: Use commas, not '=' inside where() arguments [OK]

Common Mistakes:

• Using '=' instead of ',' in method arguments
• Thinking select() must have columns
• Believing where cannot be chained

5. You want to update the email of a user with id = 5 using Knex. Which query correctly performs this update?

hard

A. knex('users').where('id', 5).update({ email: '[e-mail]' })

B. knex('users').set('email', '[e-mail]').where('id', 5)

C. knex.update('users').set('email', '[e-mail]').where('id', 5)

D. knex('users').update({ email: '[e-mail]' }).where('id' = 5)

Solution

1. Step 1: Recall correct update syntax

   Knex updates usually chain where() before update() to specify which rows to change.

2. Step 2: Evaluate each option

   knex('users').where('id', 5).update({ email: '[e-mail]' }) correctly chains where('id', 5) before update({ email: ... }). knex('users').update({ email: '[e-mail]' }).where('id' = 5) uses '=' instead of ',' causing syntax error. knex('users').set('email', '[e-mail]').where('id', 5) uses invalid set() method. knex.update('users').set('email', '[e-mail]').where('id', 5) uses invalid syntax.

3. Final Answer:

   knex('users').where('id', 5).update({ email: '[e-mail]' }) -> Option A

4. Quick Check:

   where() before update() is correct pattern [OK]

Hint: Chain where() before update() to target rows [OK]

Common Mistakes:

• Using '=' instead of ',' in where arguments
• Using non-existent set() method
• Using invalid knex.update('users') syntax