SISMEMBER for membership check in Redis - Mini Project: Build & Apply

Check Membership in a Redis Set Using SISMEMBER

📖 Scenario: You are managing a Redis database that stores a set of usernames who have access to a special feature on your website.You want to check if a particular user is in this set to grant or deny access.

🎯 Goal: Build a Redis command sequence to create a set of usernames, add users to it, and check if a specific username is a member of that set using the SISMEMBER command.

📋 What You'll Learn

Create a Redis set called feature_users with the usernames alice, bob, and charlie

Add a configuration variable check_user with the value bob

Use the SISMEMBER command to check if check_user is in the feature_users set

Complete the command sequence to perform the membership check

💡 Why This Matters

🌍 Real World

Checking user permissions or feature access quickly using Redis sets is common in web applications for fast membership tests.

💼 Career

Understanding Redis set commands and membership checks is valuable for backend developers and system administrators managing caching and user access control.

1

Create the Redis set feature_users with usernames

Write the Redis command to create a set called feature_users and add the usernames alice, bob, and charlie to it using the SADD command.

Redis

# Your Redis command here

Hint

Use the SADD command followed by the set name and the usernames separated by spaces.

2

Set the username to check in check_user

Write the Redis command to set a variable called check_user with the value bob using the SET command.

Redis

SADD feature_users alice bob charlie
# Your Redis command here

Hint

Use the SET command to assign the value bob to the key check_user.

3

Use SISMEMBER to check membership of check_user in feature_users

Write the Redis command to check if the value stored in check_user is a member of the set feature_users using the SISMEMBER command with the key feature_users and the value bob.

Redis

SADD feature_users alice bob charlie
SET check_user bob
# Your Redis command here

Hint

Use SISMEMBER with the set name and the username to check membership.

4

Complete the membership check command sequence

Add the final Redis command to retrieve the value of check_user using the GET command, so you can confirm which username you are checking membership for.

Redis

SADD feature_users alice bob charlie
SET check_user bob
SISMEMBER feature_users bob
# Your Redis command here

Hint

Use the GET command with the key check_user to retrieve its value.

Practice

1. What does the Redis command SISMEMBER do?

easy

A. Adds a value to a set

B. Removes a value from a set

C. Checks if a value is a member of a set and returns 1 or 0

D. Returns all members of a set

Solution

1. Step 1: Understand SISMEMBER purpose

   The SISMEMBER command checks membership of a value in a Redis set.

2. Step 2: Identify return values

   It returns 1 if the value is in the set, otherwise 0.

3. Final Answer:

   Checks if a value is a member of a set and returns 1 or 0 -> Option C

4. Quick Check:

   SISMEMBER returns 1 or 0 [OK]

Hint: SISMEMBER returns 1 if present, else 0 [OK]

Common Mistakes:

• Confusing SISMEMBER with SADD or SREM
• Expecting SISMEMBER to return the value itself
• Thinking SISMEMBER returns all set members

2. Which of the following is the correct syntax to check if 'apple' is in the set 'fruits' using Redis?

easy

A. SISMEMBER(fruits, apple)

B. SISMEMBER 'fruits' 'apple'

C. SISMEMBER fruits, apple

D. SISMEMBER fruits apple

Solution

1. Step 1: Recall Redis command syntax

   Redis commands use space-separated arguments without commas or parentheses.

2. Step 2: Match correct syntax

   Correct syntax is SISMEMBER key member, so SISMEMBER fruits apple is correct.

3. Final Answer:

   SISMEMBER fruits apple -> Option D

4. Quick Check:

   Redis commands use spaces, no commas or quotes needed [OK]

Hint: Use space-separated arguments without quotes or commas [OK]

Common Mistakes:

• Adding commas between arguments
• Using parentheses like a function call
• Adding quotes around arguments unnecessarily

3. Given the Redis set 'colors' contains {"red", "blue", "green"}, what is the output of SISMEMBER colors yellow?

medium

A. 0

B. 1

C. red

D. Error

Solution

1. Step 1: Check if 'yellow' is in the set 'colors'

   The set contains "red", "blue", and "green" but not "yellow".

2. Step 2: Understand SISMEMBER return value

   SISMEMBER returns 1 if member exists, else 0. Since "yellow" is not in the set, it returns 0.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Member absent = 0 [OK]

Hint: If value not in set, SISMEMBER returns 0 [OK]

Common Mistakes:

• Assuming it returns the value itself
• Confusing 0 with an error
• Thinking it returns the whole set

4. You run the command SISMEMBER colors without specifying a member. What will happen?

medium

A. Syntax error

B. Returns 1

C. Returns 0

D. Returns all members

Solution

1. Step 1: Check command argument requirements

   SISMEMBER requires exactly two arguments: the set key and the member to check.

2. Step 2: Analyze missing argument effect

   Omitting the member argument causes a syntax error in Redis.

3. Final Answer:

   Syntax error -> Option A

4. Quick Check:

   Missing arguments cause syntax error [OK]

Hint: SISMEMBER needs two arguments; missing one causes error [OK]

Common Mistakes:

• Expecting default member to be checked
• Thinking it returns 0 if member missing
• Assuming it returns all members

5. You have a Redis set 'users' with members {"alice", "bob", "carol"}. You want to check if 'dave' is a member and add him only if he is not already present. Which sequence of commands correctly does this?

hard

A. SISMEMBER users dave
SREM users dave

B. SISMEMBER users dave
SADD users dave

C. SADD users dave
SISMEMBER users dave

D. SREM users dave
SADD users dave

Solution

1. Step 1: Check membership before adding

   Use SISMEMBER to see if 'dave' is already in 'users'.

2. Step 2: Add 'dave' only if not present

   If SISMEMBER returns 0, then use SADD to add 'dave'.

3. Final Answer:

   SISMEMBER users dave SADD users dave -> Option B

4. Quick Check:

   Check membership then add if absent [OK]

Hint: Check with SISMEMBER before SADD to avoid duplicates [OK]

Common Mistakes:

• Adding before checking membership
• Removing member instead of adding
• Checking membership after adding