HMSET and HMGET for bulk in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set multiple fields in a Redis hash using HMSET.

Redis

HMSET user:1000 [1]

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

A"name" "Alice"

B"name" "Alice" "age" "30"

C"user" "1000"

D"age" "30"

Attempts:

3 left

💡 Hint

Common Mistakes

Providing only one field-value pair when multiple are needed.

Using incorrect syntax without quotes around strings.

The HMSET command requires field-value pairs to set multiple fields at once. Option B provides both fields and their values.

2fill in blank

medium

Complete the code to retrieve multiple fields from a Redis hash using HMGET.

Redis

HMGET user:1000 [1]

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

A"email"

B"user" "1000"

C"name"

D"name" "age"

Attempts:

3 left

💡 Hint

Common Mistakes

Requesting only one field when multiple are needed.

Using the key as a field name.

HMGET retrieves the values of the specified fields. To get multiple fields, list them all after the key.

3fill in blank

hard

Fix the error in the HMSET command to correctly set multiple fields.

Redis

HMSET user:1000 [1]

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

A"name" "Alice" "age" "30"

Bname Alice age 30

C"name" "Alice" age 30

Dname, Alice, age, 30

Attempts:

3 left

💡 Hint

Common Mistakes

Using commas between fields and values.

Not quoting string values.

HMSET requires each field and value to be quoted strings without commas. Option A is the correct syntax.

4fill in blank

hard

Fill both blanks to set and then get multiple fields in Redis.

Redis

HMSET user:2000 [1]
HMGET user:2000 [2]

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

A"city" "Paris" "country" "France"

B"city" "country"

C"Paris" "France"

D"country" "city"

Attempts:

3 left

💡 Hint

Common Mistakes

Using values instead of field names in HMGET.

Mixing order of fields and values.

HMSET needs field-value pairs (option A). HMGET needs the field names to retrieve (option B).

5fill in blank

hard

Fill all three blanks to set multiple fields, then retrieve them in Redis.

Redis

HMSET user:3000 [1]
HMGET user:3000 [2]
HMGET user:3000 [3]

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

A"first_name" "John" "last_name" "Doe"

B"first_name" "last_name"

C"John" "Doe"

D"age" "email"

Attempts:

3 left

💡 Hint

Common Mistakes

Using values instead of field names in HMGET.

HMSET sets fields and values (A). The first HMGET retrieves the name fields (B). The second HMGET retrieves other fields (D).

Practice

1. What does the Redis command HMSET do?

easy

A. Retrieves all keys from the database.

B. Deletes a hash key and all its fields.

C. Stores multiple fields and their values in a single hash key at once.

D. Increments a numeric value in a hash field.

Solution

1. Step 1: Understand HMSET purpose

   The HMSET command is used to save many fields and their values inside one hash key in Redis.

2. Step 2: Compare with other commands

   Other commands like DEL delete keys, and INCR increments values, so they do not match HMSET's bulk saving role.

3. Final Answer:

   Stores multiple fields and their values in a single hash key at once. -> Option C

4. Quick Check:

   HMSET saves many fields at once = B [OK]

Hint: HMSET saves many fields in one hash key at once [OK]

Common Mistakes:

• Confusing HMSET with commands that delete keys
• Thinking HMSET retrieves data instead of saving
• Mixing HMSET with single field commands like HSET

2. Which of the following is the correct syntax to set multiple fields in a hash named user:1 using HMSET?

easy

A. HMSET user:1 ["name", "Alice", "age", 30, "city", "NY"]

B. HMSET user:1 (name, "Alice", age, 30, city, "NY")

C. HMSET user:1 {name: "Alice", age: 30, city: "NY"}

D. HMSET user:1 name "Alice" age 30 city "NY"

Solution

1. Step 1: Recall HMSET syntax

   HMSET expects the key followed by field and value pairs separated by spaces, without brackets or braces.

2. Step 2: Check each option

   HMSET user:1 name "Alice" age 30 city "NY" matches the correct syntax: key, field, value, field, value... Options B, C, and D use invalid brackets or JSON-like syntax not accepted by Redis.

3. Final Answer:

   HMSET user:1 name "Alice" age 30 city "NY" -> Option D

4. Quick Check:

   HMSET syntax is key + field value pairs space-separated = A [OK]

Hint: HMSET uses space-separated field-value pairs, no brackets [OK]

Common Mistakes:

• Using brackets or braces in HMSET command
• Putting fields and values inside parentheses
• Confusing HMSET with JSON syntax

3. Given the following commands executed in Redis:
HMSET product:100 name "Laptop" price 1200 stock 30
HMGET product:100 name price
What will be the output of the HMGET command?

medium

A. ["Laptop", "1200"]

B. ["Laptop", 1200]

C. ["name", "price"]

D. ["Laptop"]

Solution

1. Step 1: Understand HMSET stored data

   The HMSET command stores fields 'name' with value "Laptop" and 'price' with value "1200" (as string) in the hash 'product:100'.

2. Step 2: Understand HMGET output

   HMGET fetches the values of the requested fields in order, returning an array of strings: ["Laptop", "1200"].

3. Final Answer:

   ["Laptop", "1200"] -> Option A

4. Quick Check:

   HMGET returns values as strings in array = A [OK]

Hint: HMGET returns values as strings in array order [OK]

Common Mistakes:

• Expecting numeric types instead of strings
• Confusing HMGET output with field names
• Getting only one value instead of array

4. You run the command HMGET user:5 name age but get (nil) for both fields. What is the most likely reason?

medium

A. Redis server is down.

B. The hash key user:5 does not exist or has no such fields.

C. HMGET cannot fetch multiple fields at once.

D. HMGET syntax requires brackets around field names.

Solution

1. Step 1: Interpret (nil) results

   Getting (nil) means the requested fields or the hash key do not exist in Redis.

2. Step 2: Check command syntax and server status

   HMGET syntax is correct without brackets, and if the server was down, no response would be received.

3. Final Answer:

   The hash key user:5 does not exist or has no such fields. -> Option B

4. Quick Check:

   (nil) means missing key or fields = D [OK]

Hint: (nil) means key or fields missing, not syntax error [OK]

Common Mistakes:

• Adding brackets around fields in HMGET
• Assuming HMGET cannot fetch multiple fields
• Thinking server down causes (nil) responses

5. You want to store user profile data with fields name, email, and age in Redis using HMSET, then retrieve only email and age with HMGET. Which sequence of commands is correct?

hard

A. HMSET user:10 name "Bob" email "[e-mail]" age 25HMGET user:10 email age

B. HMSET user:10 {name: "Bob", email: "[e-mail]", age: 25}HMGET user:10 [email, age]

C. HMSET user:10 (name "Bob", email "[e-mail]", age 25)HMGET user:10 (email age)

D. HMSET user:10 name="Bob" email="[e-mail]" age=25HMGET user:10 email age

Solution

1. Step 1: Write correct HMSET command

   HMSET requires key followed by field-value pairs separated by spaces without brackets or equals signs, so HMSET user:10 name "Bob" email "[e-mail]" age 25
   HMGET user:10 email age is correct.

2. Step 2: Write correct HMGET command

   HMGET takes the key and list of fields separated by spaces, so HMSET user:10 name "Bob" email "[e-mail]" age 25
   HMGET user:10 email age's HMGET is correct.

3. Final Answer:

   HMSET user:10 name "Bob" email "[e-mail]" age 25
   HMGET user:10 email age -> Option A

4. Quick Check:

   HMSET and HMGET use space-separated fields and values = C [OK]

Hint: Use space-separated fields and values, no brackets or equals [OK]

Common Mistakes:

• Using JSON or bracket syntax in HMSET
• Adding parentheses around fields in HMGET
• Using equals signs in HMSET command