![]() Let's get all the individuals that were born up to 1950 inclusive. It is possible to return scores as well, using the WITHSCORES argument: > zrange hackers 0 -1 withscores Use ZREVRANGE instead of ZRANGE: > zrevrange hackers 0 -1 What if I want to order them the opposite way, youngest to oldest? Here just as it does in the case of the LRANGE command). Note: 0 and -1 means from element index 0 to the last element (-1 works Good, but when we ask for sorted elements Redis does not have to do any work atĪll, it's already all sorted: > zrange hackers 0 -1 Implementation note: Sorted sets are implemented via aĭual-ported data structure containing both a skip list and a hash table, soĮvery time we add an element Redis performs an O(log(N)) operation. ![]() With sorted sets it is trivial to return a list of hackers sorted by theirīirth year because actually they are already sorted. Pairs, even if this is not used in the example above. ZADD is also variadic, so you are free to specify multiple score-value (placed before the element to be added) which is the score. > zadd hackers 1940 "Alan Kay"Īs you can see ZADD is similar to SADD, but takes one additional argument Sorted set elements, with their year of birth as "score". Let's start with a simple example, adding a few selected hackers names as B and A strings can't be equal since sorted sets only have unique elements. If B and A have exactly the same score, then A > B if the A string is lexicographically greater than the B string.If B and A are two elements with a different score, then A > B if A.score is > B.score.They are ordered according to the following rule: Ordered on request, order is a peculiarity of the data structure used to Moreover, elements in a sorted set are taken in order (so they are not (this is why the type is also similar to a hash, since every element However while elements inside sets are not ordered, every element inĪ sorted set is associated with a floating point value, called the score String elements, so in some sense a sorted set is a set as well. Like sets, sorted sets are composed of unique, non-repeating You can think of sorted sets as a mix between a Set andĪ Hash. In particular, you can use a sorted set to build a sliding-window rate limiter to prevent excessive API requests. ![]() For example, you can use sorted sets to easily maintain ordered lists of the highest scores in a massive online game. When more than one string has the same score, the strings are ordered lexicographically. Import and use BackgroundTasks with parameters in path operation functions and dependencies to add background tasks.A Redis sorted set is a collection of unique strings (members) ordered by an associated score. To see an example, check the Project Generators, they all include Celery already configured.īut if you need to access variables and objects from the same FastAPI app, or you need to perform small background tasks (like sending an email notification), you can simply just use BackgroundTasks. ![]() They tend to require more complex configurations, a message/job queue manager, like RabbitMQ or Redis, but they allow you to run background tasks in multiple processes, and especially, in multiple servers. If you need to perform heavy background computation and you don't necessarily need it to be run by the same process (for example, you don't need to share memory, variables, etc), you might benefit from using other bigger tools like Celery. You can see more details in Starlette's official docs for Background Tasks. It's still possible to use BackgroundTask alone in FastAPI, but you have to create the object in your code and return a Starlette Response including it. It is imported/included directly into FastAPI so that you can import it from fastapi and avoid accidentally importing the alternative BackgroundTask (without the s at the end) from starlette.background.īy only using BackgroundTasks (and not BackgroundTask), it's then possible to use it as a path operation function parameter and have FastAPI handle the rest for you, just like when using the Request object directly. The class BackgroundTasks comes directly from starlette.background. If there was a query in the request, it will be written to the log in a background task.Īnd then another background task generated at the path operation function will write a message using the email path parameter. In this example, the messages will be written to the log.txt file after the response is sent. From fastapi import BackgroundTasks, FastAPI app = FastAPI () def write_notification ( email : str, message = "" ): with open ( "log.txt", mode = "w" ) as email_file : content = f "notification for
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