HLEN for field count in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command HLEN do?

It returns the number of fields stored in a hash stored at a given key.

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How do you use HLEN to count fields in a hash named user:1000?

You run HLEN user:1000. It returns the count of fields inside that hash.

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What type of data structure must the key hold for HLEN to work?

The key must hold a hash data structure in Redis.

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What happens if you use HLEN on a key that does not exist?

Redis returns 0 because there are no fields in a non-existing hash.

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Can HLEN be used on other Redis data types like strings or lists?

No, HLEN only works on hashes. Using it on other types returns a type error.

What does the Redis command HLEN myhash return?

A The value of the field named 'myhash'

B Length of the string stored at 'myhash'

C Number of fields in the hash stored at key 'myhash'

D Number of elements in the list 'myhash'

HLEN returns the count of fields in a hash stored at the given key.

If the key 'profile' does not exist, what does HLEN profile return?

A 0

B An error

C null

D 1

Redis returns 0 for HLEN on a non-existing hash key.

Which Redis data type is required for HLEN to work correctly?

A Set

B List

C String

D Hash

HLEN works only on hashes.

What happens if you run HLEN on a key holding a string?

A Returns the string length

B Returns an error

C Returns 0

D Returns the number of characters

Using HLEN on non-hash types causes a type error.

Which command would you use to find how many fields are in a Redis hash?

A HLEN

B LLEN

C SCARD

D STRLEN

HLEN returns the number of fields in a hash.

Explain what the Redis command HLEN does and when you would use it.

Think about how you count items in a collection.

Describe what happens if you run HLEN on a key that holds a string instead of a hash.

Consider data types and command compatibility.