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Redis HMSET in Ruby (Detailed Guide w/ Code Examples)

Use Case(s)

Using HMSET command in Redis with Ruby is common when you need to set multiple field-value pairs to a hash stored at key. It is extensively used where applications need to store and fetch data like user profiles, session information, etc., in a structured manner.

Code Examples

In Ruby, we use the redis-rb gem to interact with a Redis server. Below are some examples of using the HMSET command:

  1. Setting multiple field-value pairs to a hash:
require 'redis' redis = # Set multiple fields to a hash redis.hmset("user:1001", "name", "John Doe", "email", "")

This code connects to a local Redis server, then it uses hmset to set two fields ('name' and 'email') with their corresponding values for the hash at key 'user:1001'.

  1. Using a Hash argument instead:
require 'redis' redis = # Set multiple fields using a Hash argument user_info = {"name" => "John Doe", "email" => ""} redis.mapped_hmset("user:1001", user_info)

Here, we're using the mapped_hmset method which allows us to pass a Ruby Hash object, mapping the field names to their respective values.

Best Practices

  • Try to group related fields together in one hash. This improves readability and maintainability.
  • The field names should be descriptive enough to understand the context without needing additional comments or documentation.

Common Mistakes

  • Make sure the Redis server is running and accessible from your Ruby application.
  • Field-value pair arguments must come in pairs. If they don't, you'll get a 'wrong number of arguments' error.


  1. Can I update the values of existing fields using HMSET? Yes, if a field already exists in the hash, its value will be updated with the new value provided.

  2. What happens if the key does not exist when I try to use HMSET? Redis will automatically create a new hash and then set the field-value pairs.

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