Redis data model (key-value) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a key named 'user:1' with the value 'Alice'.

Redis

SET user:1 [1]

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

Auser

BAlice

C1

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using the key name as the value

Using a number instead of the name

The SET command stores the value 'Alice' under the key 'user:1'.

2fill in blank

medium

Complete the code to get the value stored at key 'session:123'.

Redis

GET [1]

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

Auser:123

Bsession

Csession:123

D123

Attempts:

3 left

💡 Hint

Common Mistakes

Using only part of the key

Using a value instead of a key

The GET command retrieves the value stored at the key 'session:123'.

3fill in blank

hard

Fix the error in the command to delete the key 'cache:item'.

Redis

DEL [1]

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

Acache:item

Bcacheitem

Ccache_item

Dcache-item

Attempts:

3 left

💡 Hint

Common Mistakes

Replacing colon with dash or underscore

Using partial key names

The key name must match exactly. The key is 'cache:item' with a colon, not a dash or underscore.

4fill in blank

hard

Fill both blanks to set a key 'product:45' with value 'Book' and then retrieve it.

Redis

[1] product:45 Book
[2] product:45

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

ASET

BGET

CDEL

DEXPIRE

Attempts:

3 left

💡 Hint

Common Mistakes

Using DEL instead of GET to retrieve

Using EXPIRE instead of SET to store

First, use SET to store the value 'Book' at 'product:45'. Then use GET to retrieve it.

5fill in blank

hard

Fill all three blanks to set a key 'order:100' with value 'Pending', update it to 'Shipped', and then get the updated value.

Redis

[1] order:100 Pending
[2] order:100 Shipped
[3] order:100

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

ADEL

BSET

CGET

DEXPIRE

Attempts:

3 left

💡 Hint

Common Mistakes

Using DEL to update a key

Using EXPIRE instead of SET

Trying to GET before setting a value

Use SET to create and update the key's value, then GET to retrieve the latest value.

Practice

1. What is the main purpose of the key in a Redis key-value data model?

easy

A. To store multiple values together

B. To uniquely identify the stored data

C. To perform calculations on data

D. To format the data for display

Solution

1. Step 1: Understand the role of keys in Redis

   Keys in Redis act as unique names that identify each piece of data stored.

2. Step 2: Differentiate keys from values

   Values hold the actual data, while keys are used to find or access that data quickly.

3. Final Answer:

   To uniquely identify the stored data -> Option B

4. Quick Check:

   Key = Unique identifier [OK]

Hint: Keys uniquely name data for fast access [OK]

Common Mistakes:

• Thinking keys store multiple values
• Confusing keys with data formatting
• Assuming keys perform calculations

2. Which of the following is the correct Redis command syntax to set a key named user:1 with value John?

easy

A. STORE user:1 John

B. GET user:1 John

C. SET user:1 John

D. SET user:1 = John

Solution

1. Step 1: Recall the Redis command to store a key-value pair

   The command to set a key with a value is SET key value.

2. Step 2: Check each option's syntax

   SET user:1 John matches the correct syntax. Options A, B, and C use incorrect commands or syntax.

3. Final Answer:

   SET user:1 John -> Option C

4. Quick Check:

   SET key value = correct syntax [OK]

Hint: Use SET key value to store data [OK]

Common Mistakes:

• Using GET instead of SET to store data
• Adding '=' sign in command
• Using STORE command which doesn't exist

3. Given the following Redis commands executed in order:

SET counter 10
INCR counter
GET counter

What will be the output of the last command?

medium

A. 11

B. 10

C. counter

D. Error

Solution

1. Step 1: Analyze the commands executed

   First, SET counter 10 sets the key counter to string "10". Then, INCR counter increments the numeric value by 1.

2. Step 2: Understand the effect of INCR and GET

   INCR converts the string "10" to number 10, adds 1 to make 11, and stores it back. GET returns the current value, which is now "11".

3. Final Answer:

   11 -> Option A

4. Quick Check:

   10 + 1 = 11 [OK]

Hint: INCR adds 1 to numeric string values [OK]

Common Mistakes:

• Assuming GET returns the key name
• Thinking INCR works on non-numeric strings
• Expecting no change after INCR

4. You run the command INCR mykey but get an error. Which of the following is the most likely cause?

medium

A. The command syntax is incorrect

B. The key mykey does not exist

C. The Redis server is down

D. The value of mykey is not an integer

Solution

1. Step 1: Understand INCR command requirements

   INCR requires the key's value to be an integer or not exist (which initializes it to 0).

2. Step 2: Identify error cause

   If the key exists but holds a non-integer value (like a string), INCR will cause an error.

3. Final Answer:

   The value of mykey is not an integer -> Option D

4. Quick Check:

   INCR needs integer value [OK]

Hint: INCR fails if value is non-integer [OK]

Common Mistakes:

• Assuming missing key causes error
• Blaming server status without checking value
• Thinking syntax is wrong when command is correct

5. You want to store user session data in Redis using the key-value model. Which approach best ensures each session is uniquely stored and easily retrieved?

hard

A. Use a key pattern like session:{session_id} with the session data as the value

B. Store all sessions in a single key as a JSON string

C. Use the same key session for all users and overwrite values

D. Store session data as keys and user IDs as values

Solution

1. Step 1: Understand unique key requirements for sessions

   Each user session must have a unique key to avoid overwriting and allow quick access.

2. Step 2: Evaluate options for storing sessions

   Use a key pattern like session:{session_id} with the session data as the value uses a unique key pattern with session IDs, which is best practice. Store all sessions in a single key as a JSON string stores all sessions in one key, making access slow and complex. Use the same key session for all users and overwrite values overwrites data. Store session data as keys and user IDs as values reverses key-value roles, which is inefficient.

3. Final Answer:

   Use a key pattern like session:{session_id} with the session data as the value -> Option A

4. Quick Check:

   Unique keys per session = best practice [OK]

Hint: Use unique keys with session IDs for each session [OK]

Common Mistakes:

• Storing all sessions in one key
• Overwriting session data with same key
• Confusing keys and values roles