The HMGET
command in Redis is commonly used when there's a need to retrieve multiple field values from a hash stored at a specific key. In the context of Python, Redis' HMGET
is often used in applications that require high-speed access to structured data like user profiles, stateful data, or cached web pages.
Let's say we have a hash representing a User, with fields like "name", "email", and "age". You can use HMGET
to fetch multiple fields at once.
Here's an example using the redis-py library:
import redis r = redis.Redis(host='localhost', port=6379, db=0) # Set some initial values r.hmset("user:1000", {"name": "Jack", "email": "jack@example.com", "age": 30}) # Get multiple field values values = r.hmget("user:1000", "name", "email") print(values) # Output: [b'Jack', b'jack@example.com']
The hmget
method takes the key of the hash and the field names you want to retrieve. It returns a list of values corresponding to the given field names.
HMGET
will return a None
value for that field.HMGET
instead of multiple HGET
commands if you need to get multiple fields from a hash. It reduces the number of round-trip times between your application and Redis server.HMGET
on non-hash keys: If the key exists in the database but its associated value is not a hash, an error will be returned.None
values in the return list: If a field does not exist in the hash, HMGET
will return None
for that field.Q: Can I use HMGET to get all fields from a hash?
A: No, HMGET
requires you to specify the fields you want to retrieve. If you want to get all fields and their values, use HGETALL
.
Q: What if the specified key does not exist in Redis?
A: If the key does not exist, HMGET
simply returns None
values for all requested fields.
Dragonfly is fully compatible with the Redis ecosystem and requires no code changes to implement.