LPUSH

Introduction and Use Case(s)

The LPUSH command in Redis is used to insert one or more elements at the head of a list. This can be useful for queue implementations, task scheduling, or simply maintaining a list where new entries should appear first.

Syntax

  1. LPUSH key element [element ...]

Parameter Explanations

  • key: The name of the list.
  • element: One or more elements to insert at the head of the list.

Return Values

LPUSH returns an integer representing the length of the list after the push operation.

Example:

  1. (integer) 3

Code Examples

  1. dragonfly> LPUSH mylist "world"
  2. (integer) 1
  3. dragonfly> LPUSH mylist "hello"
  4. (integer) 2
  5. dragonfly> LPUSH mylist "!"
  6. (integer) 3
  7. dragonfly> LRANGE mylist 0 -1
  8. 1) "!"
  9. 2) "hello"
  10. 3) "world"

Best Practices

  • Pre-check if the list exists to avoid unintended behavior when working with non-list data types.
  • Use LPUSH in combination with LTRIM to maintain a fixed list size, helpful for queue management.

Common Mistakes

  • Incorrect Data Type: Using LPUSH on a key that holds a non-list value will result in an error. Always ensure the key corresponds to a list.
  • Order Confusion: Remember that LPUSH adds elements to the head (left end), not the tail (right end) of the list.

FAQs

What happens if the list does not exist?

If the list does not exist, LPUSH creates it before inserting elements.

Can I insert multiple elements at once?

Yes, you can specify multiple elements, and they will be inserted in the same order as provided from left to right.

How can I ensure that the list does not grow indefinitely?

Use LTRIM in combination with LPUSH to keep the list length within a certain limit.

  1. dragonfly> LPUSH mylist "new_element"
  2. (integer) 4
  3. dragonfly> LTRIM mylist 0 2
  4. OK