Object storage with hashes in Redis - Mini Project: Build & Apply

Object Storage with Hashes in Redis

📖 Scenario: You are managing a small online bookstore. You want to store information about books such as title, author, and price in Redis using hashes. This will help you quickly retrieve and update book details.

🎯 Goal: Build a Redis hash to store book details with fields for title, author, and price. Then add a helper variable for a book ID, update the hash with core book data, and finally add a field for stock quantity.

📋 What You'll Learn

Create a Redis hash key named book:1001 to store book details

Add a variable book_id with the value 1001

Use HSET to add fields title, author, and price to the hash

Add a new field stock with the value 30 to the hash

💡 Why This Matters

🌍 Real World

Storing objects like books in Redis hashes allows fast access and updates for web applications such as online stores.

💼 Career

Understanding Redis hashes is useful for backend developers working with caching, session storage, or real-time data storage.

1

Create a Redis hash key for the book

Create a Redis hash key named book:1001.

Redis

# Your code here to create the hash key book:1001

Hint

Use the HSET command with the key book:1001 and field book_id value "1001".

2

Add a variable for the book ID

Create a variable called book_id and set it to the string "1001".

Redis

HSET book:1001 book_id "1001"
# Your code here to create the variable book_id

Hint

Assign the string "1001" to the variable book_id.

3

Add book details to the hash

Use HSET with the key book:1001 to add fields title with value "Redis Basics", author with value "Jane Doe", and price with value 19.99.

Redis

HSET book:1001 book_id "1001"
book_id = "1001"
# Your code here to add title, author, and price fields

Hint

Use one HSET command to add all three fields and their values.

4

Add stock quantity to the book hash

Add a new field stock with the value 30 to the Redis hash key book:1001 using HSET.

Redis

HSET book:1001 book_id "1001"
book_id = "1001"
HSET book:1001 title "Redis Basics" author "Jane Doe" price "19.99"
# Your code here to add stock field

Hint

Use HSET again to add the stock field with value 30.

Practice

1. What does a Redis hash store?

easy

A. A set of unique keys without duplicates

B. Only a single string value per key

C. A list of keys without values

D. Multiple fields and their values under one key

Solution

1. Step 1: Understand Redis hash structure

   Redis hashes store multiple field-value pairs grouped under a single key.

2. Step 2: Compare options with hash definition

   Only Multiple fields and their values under one key correctly describes storing multiple fields and values under one key.

3. Final Answer:

   Multiple fields and their values under one key -> Option D

4. Quick Check:

   Hashes = multiple fields + values [OK]

Hint: Hashes group fields and values under one key [OK]

Common Mistakes:

• Thinking hashes store only one value
• Confusing hashes with lists or sets
• Assuming keys are stored without values

2. Which Redis command correctly adds a field 'name' with value 'Alice' to a hash key 'user:1'?

easy

A. HGET user:1 name Alice

B. HSET user:1 name Alice

C. SET user:1 name Alice

D. HMGET user:1 name Alice

Solution

1. Step 1: Identify command to add/update hash field

   HSET is the Redis command to set a field in a hash.

2. Step 2: Check command syntax

   HSET key field value is correct; so HSET user:1 name Alice is valid.

3. Final Answer:

   HSET user:1 name Alice -> Option B

4. Quick Check:

   HSET adds/updates hash fields [OK]

Hint: Use HSET to add or update hash fields [OK]

Common Mistakes:

• Using HGET instead of HSET to add data
• Using SET which is for strings, not hashes
• Confusing HMGET (retrieves multiple fields) with HSET

3. Given the following Redis commands executed in order:
HSET user:2 age 30
HSET user:2 name Bob
HGETALL user:2
What is the output of HGETALL user:2?

medium

A. ["age", 30, "name", "Bob"]

B. ["user:2", "age", "30", "name", "Bob"]

C. ["age", "30", "name", "Bob"]

D. ["name", "Bob"]

Solution

1. Step 1: Understand HSET commands

   HSET adds fields 'age' with '30' and 'name' with 'Bob' to hash 'user:2'.

2. Step 2: Understand HGETALL output format

   HGETALL returns an array of field-value pairs as strings in order added.

3. Final Answer:

   ["age", "30", "name", "Bob"] -> Option C

4. Quick Check:

   HGETALL returns all fields and values as string pairs [OK]

Hint: HGETALL returns flat list of field-value strings [OK]

Common Mistakes:

• Expecting key name in output
• Mixing data types (number vs string)
• Only getting one field instead of all

4. You run the command HGET user:3 email but get a null response. What could be the reason?

medium

A. The field 'email' does not exist in the hash 'user:3'

B. The key 'user:3' is a string, not a hash

C. The Redis server is down

D. The command syntax is incorrect

Solution

1. Step 1: Understand HGET behavior

   HGET returns null if the field does not exist in the hash.

2. Step 2: Check other options

   Key being a string would cause an error, not null; server down or syntax error would cause different errors.

3. Final Answer:

   The field 'email' does not exist in the hash 'user:3' -> Option A

4. Quick Check:

   Missing field in hash returns null [OK]

Hint: Null means field missing, not syntax or server error [OK]

Common Mistakes:

• Assuming null means server or syntax error
• Confusing key type errors with missing field
• Expecting error instead of null for missing field

5. You want to store user profiles with fields 'name', 'age', and 'email' in Redis hashes. Which approach is best to retrieve all user data efficiently?

hard

A. Store each user as a separate hash with key 'user:<id>' and use HGETALL to get all fields

B. Store all users in one hash with fields like 'user1_name', 'user1_age', 'user2_name', etc.

C. Store each field as a separate key like 'name:<id>', 'age:<id>', 'email:<id>'

D. Store user data as JSON strings in simple keys

Solution

1. Step 1: Analyze storage options

   Storing each user as a separate hash groups related fields logically and allows efficient access.

2. Step 2: Evaluate retrieval efficiency

   Using HGETALL on 'user:<id>' fetches all fields at once, simpler and faster than scattered keys or complex parsing.

3. Final Answer:

   Store each user as a separate hash with key 'user:<id>' and use HGETALL to get all fields -> Option A

4. Quick Check:

   Separate hashes per user = organized and efficient [OK]

Hint: Use one hash per user for grouped fields and easy retrieval [OK]

Common Mistakes:

• Mixing all users in one hash causing complex keys
• Using separate keys for each field complicates retrieval
• Storing JSON loses Redis hash benefits