In Redis, to store an array of objects we should use hash for the object and add its key to a list:
HMSET concept:unique_id name "concept"
...
LPUSH concepts concept:unique_id
...
I want to retrieve all hash values (or objects) in the list, but the list contains only hash keys so a two step command is necessary, right? This is how I'm doing in python:
def get_concepts():
list = r.lrange("concepts", 0, -1)
pipe = r.pipeline()
for key in list:
pipe.hgetall(key)
pipe.execute()
Is it necessary to iterate and fetch each individual item? Can it be more optimized?
You can use the SORT command to do this:
SORT concepts BY nosort GET concept:*->name GET concept:*->some_key
Where * will expand to each item in the list.
Add LIMIT offset count for pagination.
Note that you have to enumerate each field in the hash (each field you want to fetch).
Another option is to use the new (in redis 2.6) EVAL command to execute a Lua script in the redis server, which could do what you are suggesting, but server side.
Related
Using sort one can sort a set and get external keys using results from the sort component of query.
By way of example:
If the external key/value are defined as various keys using the pattern:itemkey:<somestring>
And a sorted list has list of the members then issuing command sort <lists key> by nosort get itemkey:* would get the values of the referenced keys.
I would like to be able to sort through a sorted list and delete these individual keys but it appears that sort <key> by nosort del itemkey:* is not supported.
Any suggestions on how to get list of values stored in a set and then delete the external keys?
Obviously I can do this with two commands, first getting the list of values and then by iterating through list call the delete function - but this is not desirable as I requite atomic operation.
To ensure atomic operation one can use either transactions or redis' lua scripts. For efficiency I decided to go with using script. This way the entire script is completed before next redis action/request is processed.
In code snippet below. I used loadScript in order to store script redis side reducing traffic with every call, the response from loadScript is then used as identifier to Jedis's evalsha command.
Using Scala (Note Jedis is a Java library, hence the .asJava):
val scriptClearIndexRecipe = """local names = redis.call('SORT', KEYS[1]);
| for i, k in ipairs(names) do
| redis.call('DEL', "index:recipe:"..k)
| end;
| redis.call('DEL', KEYS[1]);
| return 0;""".stripMargin
def loadScript(script: String): String = client.scriptLoad(script)
def eval(luaSHA: String, keys: List[String], args: List[String]): AnyRef = {
client.evalsha(luaSHA, keys.asJava, args.asJava)
}
For example, I have stored a value under some keys in redis with prefix doc:
doc:office:room_1
doc:office:room_2
doc:reception
Let's say I want to find key prefix doc:office:
How can I fastly search keys by prefix beside KEYS, SCAN command?
I have checked Redis Search, but it works only on fields not on the keys itself.
Can I add index keys somehow?
You could manage an index yourself. For example, you could have a Set called doc:office. Whenever you add or remove a key that starts with doc:office, you could add or remove that string from the Set. Then, if you need all the keys with that prefix, just get the members of the Set.
Like this:
> SET doc:office:room_1 data
> SADD doc:office doc:office:room_1
> SET doc:office:room_2 moardata
> SADD doc:office doc:office:room_2
> SMEMBERS doc:office
1) doc:office:room_1
2) doc:office:room_2
I am new to Redis I tried to figure out this problem going through Redis documentation but no luck. Here are the details.
Lets say I inserted Strings like below.
Set category:1 "Men"
Set category:2 "Women"
Set category:3 "Kids"
Set category:4 "Home"
Set category:5 "shoes" ...
Now I want to get all the values by querying with keys which follow certain pattern in this case category:*.
Get category:*
Is there any way to get all categories like this?
Use SCAN. SCAN is the only safe way to iterate through the keys in a Redis database. SCAN will chunk out a portion of the keyspace and return a cursor (always the first result) and any values it found in that chunk. You start with a cursor of 0.
> SCAN 0 MATCH "category:*"
1) "1904"
2) (empty list or set)
Then you pass that cursor back into the SCAN command with the same pattern:
> SCAN 1904 MATCH "category:*"
1) "0"
2) 1) "category:3"
2) "category:2"
3) "category:4"
4) "category:1"
In this case the cursor returned is 0 which is the signal that the SCAN command has completed. The second response is an array with the keys found. Note that you need to run the SCAN command in a loop and none or only part of keys that match the pattern will be returned each time.
After you get the keys, you'll need to retrieve the values as normal (GET).
Just a note: From the look of how your data is structured, you're likely using an inappropriate data type: The categories would be better organized into a hash (e.g. HSET categories 1 men then you can use HGETALL)
I have checked following, but didn't work.
https://redis.io/commands/keys
KEYS Room:*
1) "Room:120"
2) "Room:121"
3) "Room:122"
Following is the redis key/values (HMSET)
Room:120 [SocketId:mOQDJusPjDTBN5L-AAAC,TimeStamp:10-10-2017 12:10:00 AM]
Room:121 ....
Room:122 ....
...
Need to search as Room:* SocketId:mOQDJusPjDTBN5L-AAAC
How can I search for SocketId in the collection ?
Need to search with:
mOQDJusPjDTBN5L-AAAC
The question is not so clear
as u mentioned hmset i am assuming that you are using hashes to store your data.
As per your data,
'room120' should be the key, 'socketId' should be the field and 'mOQDJusPjDTBN5L-AAAC' should be the value.
so in order to search for socketId you can use hscan,where hscan iterates through the field of a particular key.https://redis.io/commands/scan
in case if you are just using key/value storage i.e
'socketId' being the key ,'mOQDJusPjDTBN5L-AAAC' being the value.
here u can just use the command Keys *socket*to search for the key socketId
I'm iterating through data and dumping some to a Redis DB. Here's an example:
hmset id:1 username "bsmith1" department "accounting"
How can I increment the unique ID on the fly and then use that during the next hmset command? This seems like an obvious ask but I can't quite find the answer.
Use another key, a String, for storing the last ID. Before calling HMSET, call INCR on that key to obtain the next ID. Wrap the two commands in a MULTI/EXEC block or a Lua script to ensure the atomicity of the transaction.
Like Itamar mentions you can store your index/counter in a separate key. In this example I've chosen the name index for that key.
Python 3
KEY_INDEX = 'index'
r = redis.from_url(host)
def store_user(user):
r.incr(KEY_INDEX, 1) # If key doesn't exist it will get created
index = r.get(KEY_INDEX).decode('utf-8') # Decode from byte to string
int_index = int(index) # Convert from string to int
result = r.set('user::%d' % int_index, user)
...
Note that user::<index> is an arbitrary key chosen by me. You can use whatever you want.
If you have multiple machines writing to the same DB you probably want to use pipelines.