I just learned that when a list is empty, EXISTS returns 0.
I am processing a list using this:
rpoplpush source target
When I am done processing, I still want to look at the source to see if it is empty, but also if the key exists. But since the list is empty, it is returning 0.
EXISTS source
(integer) 0
Is there a way to know that your list is empty, but the key does exist still in redis?
In redis, empty list can't exist. If after popping an element list becomes empty, it is deleted.
if (listTypeLength(o) == 0) {
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",
c->argv[1],c->db->id);
dbDelete(c->db,c->argv[1]);
}
Related
I'm new to Aerospike and am probably missing something fundamental, but I'm trying to see an enumeration of the Keys in a Set (I'm purposefully avoiding the word "list" because it's a datatype).
For example,
To see all the Namespaces, the docs say to use SHOW NAMESPACES
To see all the Sets, we can use SHOW SETS
If I want to see all the unique Keys in a Set ... what command can I use?
It seems like one can use client.scan() ... but that seems like a super heavy way to get just the key (since it fetches all the bin data as well).
Any recommendations are appreciated! As of right now, I'm thinking of inserting (deleting) into (from) a meta-record.
Thank you #pgupta for pointing me in the right direction.
This actually has two parts:
In order to retrieve original keys from the server, one must -- during put() calls -- set policy to save the key value server-side (otherwise, it seems only a digest/hash is stored?).
Here's an example in Python:
aerospike_client.put(key, {'bin': 'value'}, policy={'key': aerospike.POLICY_KEY_SEND})
Then (modified Aerospike's own documentation), you perform a scan and set the policy to not return the bin data. From this, you can extract the keys:
Example:
keys = []
scan = client.scan('namespace', 'set')
scan_opts = { 'concurrent': True, 'nobins': True, 'priority': aerospike.SCAN_PRIORITY_MEDIUM }
for x in (scan.results(policy=scan_opts)): keys.append(x[0][2])
The need to iterate over the result still seems a little clunky to me; I still think that using a 'master-key' Record to store a list of all the other keys will be more performant, in my case -- in this way, I can simply make one get() call to the Aerospike server to retrieve the list.
You can choose not bring the data back by setting includeBinData in ScanPolicy to false.
I want to check if an entity is part of the users input.
Example:
entities['#PRODUKT_INTENT_STOP_LIST']?.contains($variables.tmpEntity)
As you can see by this example, the value of the entity#PRODUKT_INTENT_STOP_LIST
is a variable. I put this at a condition for a node, but this is not working.
If I use a hardcoded string instead of the variable it is working fine.
entities['#PRODUKT_INTENT_STOP_LIST']?.contains('Chart') works fine
but setting $variables.tmpEntity to 'Chart' a and then ask for
entities['#PRODUKT_INTENT_STOP_LIST']?.contains($variables.tmpEntity)
is not working.
Can someone tells me what's wrong here?
Still trying to understand what you are trying to do.But if you want to check whether an entity exist in your input or not you can do it by applying condition on size of that entity.
"context":{
"size":"<?#Entity.size()?>"
}
now if size is equals to 0 then entity does not exist.
I know this is a longer way but it also tells you how many times does that entity exist in your input.
Hi I used the wrong statement.
This statement should work:
entities[PRODUKT_INTENT_STOP_LIST]?.get($variables.countEntity).value==$variables.$variables.tmpEntity
$variables.countEntity : counter to iterate thru entity array #PRODUKT_INTENT_STOP_LIST to check if an entity value is equal $variables.tmpEntity
Regards
I tried adding some sample score-value pairs to redis sorted set using below code:
String key = "set";
redis.zadd(key, 5, "1034");
redis.zadd(key, 2, "1030");
redis.zadd(key, 1, "1089");
and tried retrieving it using byteArray and BitSet
byte[] byteArr = redis.get(key.getBytes());
BitSet bitSet = fromByteArrayReverse(byteArr);
System.out.println(bitset.toString()));
also i tried executing
System.out.println(redis.get(key.getBytes()));
which is supposed to give me an address of the byte-array
But for both of these commands i get the error
" ERR Operation against a key holding the wrong kind of value"
So can anyone please tell me why does this error occur in the first place and also the correct redis command/code to retrieve values from a redis sorted-set??
What you want is calling
ZSCORE key "1034"
Or in the case of wanting only elements between two particular scores
ZRANGEBYSCORE key lower upper
Since you also have "rank" (position or index, as in a list) you can also ask for example for the first three elements in your set
ZRANGEBYRANK key 0 2
The error you are getting is because once you assign a value to a key, that value defines the type of the internal structure on redis, and you can only use commands for that particular structure (or generic key commands such as DEL and so on). In your case you are trying to mix sorted sets with byte operations and it doesn't match.
To see all sorted set commands, please refer to http://redis.io/commands#sorted_set
Is there any way to do an atomic set only if not already set in Redis?
Specifically, I'm creating a user like "myapp:user:user_email" and want Redis to give me back an error if "user_email" is already taken, instead of silently replacing the old value. Something like declare, not replace.
See SETNX
Set key to hold string value if key does not exist. In that case, it is equal to SET. When key already holds a value, no operation is performed. SETNX is short for "SET if N ot e X ists".
You can check the return value. If it is 0, the key was not set, implying it already existed.
How can we avoid multiple iteration to search for an object's property and if found then assign it to a variable else search for another key ?
eq we have Video Class with one of the field as videoType which can have values as hq(high-quality),normal(normal), def(default)..etc and so on.
From an array containing multiple video objects, how can we search and return a particular object in an order that if the array contains object with property hq then first return it,else search for normal and proceed so on. if a set of n keys are to be tested in the key set (hq,normal,def,....) then do we always need to iterate the entire array "n" times unless the key is found.
Can this be done is single iteration ? Do we need to first sort the original array in the order of occurrence of the keys in desired key set. I hope my problem statement is clear.
One possible solution for this would be to create separate NSMutableArrays for each videoType. Then, as you iterate once over your array of video objects, you check its array type and add the video to the correct array.
After you finished iterating, you create the final mutable array by concatenating the other array with addObjectsFromArray.
If you have a lot or variable list of video types, you can create the separate mutable arrays as values in an NSDictionary, where the keys are the video types. This way, you can get the target array with one step, by fetching it from the dictionary.