HKEYS and HVALS in Redis - Mini Project: Build & Apply

Using HKEYS and HVALS in Redis

📖 Scenario: You are managing a small online store's inventory using Redis. You want to store product details in a hash and then retrieve all the product names and their prices separately.

🎯 Goal: Build a Redis hash to store product names and prices, then use HKEYS to get all product names and HVALS to get all prices.

📋 What You'll Learn

Create a Redis hash called products with exact entries: "apple": "1.20", "banana": "0.50", "cherry": "2.00"

Set a variable hash_name to the string "products"

Use the HKEYS command on products to get all product names

Use the HVALS command on products to get all product prices

💡 Why This Matters

🌍 Real World

Redis hashes are useful for storing related data like product details, user profiles, or settings in a fast and organized way.

💼 Career

Knowing how to use Redis hashes and commands like HKEYS and HVALS is valuable for backend developers and database administrators working with caching and fast data retrieval.

1

DATA SETUP: Create the Redis hash with product data

Create a Redis hash called products with these exact entries: "apple": "1.20", "banana": "0.50", and "cherry": "2.00" using the HSET command.

Redis

# Use HSET to create the products hash with the given entries
# Your code here

Hint

Use HSET followed by the hash name products and then pairs of field and value.

2

CONFIGURATION: Set the hash name variable

Set a variable called hash_name to the string "products".

Redis

HSET products apple 1.20 banana 0.50 cherry 2.00
# Set hash_name variable to "products"
# Your code here

Hint

Use the SET command to assign the string "products" to hash_name.

3

CORE LOGIC: Retrieve all product names using HKEYS

Use the HKEYS command on products to get all the product names stored in the hash.

Redis

HSET products apple 1.20 banana 0.50 cherry 2.00
SET hash_name "products"
# Use HKEYS products to get all product names
# Your code here

Hint

Use HKEYS followed by the hash name to get all keys (product names).

4

COMPLETION: Retrieve all product prices using HVALS

Use the HVALS command on products to get all the product prices stored in the hash.

Redis

HSET products apple 1.20 banana 0.50 cherry 2.00
SET hash_name "products"
HKEYS products
# Use HVALS products to get all product prices
# Your code here

Hint

Use HVALS followed by the hash name to get all values (product prices).

Practice

1. What does the Redis command HKEYS myhash return?

easy

A. All the field names (keys) inside the hash myhash

B. All the values inside the hash myhash

C. The number of fields in the hash myhash

D. Deletes the hash myhash

Solution

1. Step 1: Understand the purpose of HKEYS

   The command HKEYS is used to get all the field names (keys) from a Redis hash.

2. Step 2: Apply to the given hash

   When you run HKEYS myhash, it returns all the keys inside myhash, not the values or count.

3. Final Answer:

   All the field names (keys) inside the hash myhash -> Option A

4. Quick Check:

   HKEYS returns keys = A [OK]

Hint: HKEYS always lists keys, not values or counts [OK]

Common Mistakes:

• Confusing HKEYS with HVALS
• Thinking it returns values instead of keys
• Assuming it returns the count of fields

2. Which of the following is the correct syntax to get all values from a Redis hash named user:100?

easy

A. HVALS user:100

B. HKEYS user:100

C. HGETALL user:100

D. HVALS(user:100)

Solution

1. Step 1: Identify the command to get all values

   The Redis command to get all values from a hash is HVALS.

2. Step 2: Check syntax correctness

   The correct syntax is HVALS keyname, so HVALS user:100 is correct. Parentheses are not used in Redis commands.

3. Final Answer:

   HVALS user:100 -> Option A

4. Quick Check:

   HVALS syntax = HVALS key [OK]

Hint: HVALS command syntax: HVALS key (no parentheses) [OK]

Common Mistakes:

• Using parentheses like a function call
• Mixing HKEYS and HVALS commands
• Using HGETALL instead of HVALS for values only

3. Given a Redis hash product:1 with fields and values:
{"name": "Pen", "color": "blue", "price": "1.5"}
What will HVALS product:1 return?

medium

A. ["name", "color", "price"]

B. ["Pen", "blue", "1.5"]

C. ["product:1"]

D. An error because HVALS needs a list

Solution

1. Step 1: Understand what HVALS returns

   HVALS returns all the values stored in the hash fields, not the keys.

2. Step 2: Apply to the given hash

   The values are "Pen", "blue", and "1.5". So the command returns these values as a list.

3. Final Answer:

   ["Pen", "blue", "1.5"] -> Option B

4. Quick Check:

   HVALS returns values list = A [OK]

Hint: HVALS returns only values, not keys or errors [OK]

Common Mistakes:

• Confusing keys with values
• Expecting field names instead of values
• Thinking HVALS returns the hash key name

4. You run HKEYS myhash but get an empty list even though you know myhash has data. What could be the problem?

medium

A. The Redis server is down

B. You typed HVALS myhash instead of HKEYS

C. myhash is not a hash type but a string or other type

D. The hash myhash is empty

Solution

1. Step 1: Check the data type of the key

   If myhash is not a hash but a string or other type, HKEYS returns an empty list.

2. Step 2: Understand why other options are incorrect

   Typing HVALS would return values, not empty list. Server down causes connection errors, not empty list. An empty hash would return empty list but question says it has data.

3. Final Answer:

   myhash is not a hash type but a string or other type -> Option C

4. Quick Check:

   Wrong type key = empty HKEYS result [OK]

Hint: Empty HKEYS often means key is wrong type, not empty hash [OK]

Common Mistakes:

• Assuming empty list means empty hash
• Ignoring key data type
• Thinking server down returns empty list

5. You want to list all field names and values from a Redis hash session:123 but only want the values that are not empty strings. Which approach using HKEYS and HVALS is best?

hard

A. Use HVALS session:123 and remove empty strings from the returned list

B. Use HKEYS session:123 only, empty values are not returned

C. Use HGETALL session:123 and filter out empty values in your application

D. Use HKEYS session:123 to get keys, then filter values by fetching each with HGET and checking for empty strings

Solution

1. Step 1: Understand what HKEYS and HVALS return

   HKEYS returns all field names, HVALS returns all values including empty strings.

2. Step 2: Choose a method to filter empty values

   Since HVALS returns all values without keys, filtering empty strings is hard without knowing which value belongs to which key. Using HKEYS to get keys, then fetching each value with HGET allows filtering empty strings precisely.

3. Step 3: Evaluate other options

   HVALS alone does not provide keys, so filtering loses context. HGETALL returns all keys and values but question asks about HKEYS and HVALS usage. Using only HKEYS does not get values.

4. Final Answer:

   Use HKEYS to get keys, then fetch and filter values with HGET -> Option D

5. Quick Check:

   Filter empty values by keys + HGET = B [OK]

Hint: Get keys first, then fetch values to filter empty strings [OK]

Common Mistakes:

• Filtering values without keys loses context
• Assuming HVALS excludes empty strings
• Using only HKEYS without fetching values