Redis add element value to a set in a transaction

Question

I'm very new to redis and I'm trying to do the following inside a tranaction:

increment key add incremented value from before to a set

using redis commands it would be something like

multi
i = incr "value"
sadd "set" i
exec

Is there any redis command that would do that in one step with out needing two transactions and handling the value from the code (python code in my case)?

Many thanks

seppo0010 · Accepted Answer · 2011-11-30 01:53:31Z

3

Unfortunately you can't do that directly. You can use a MULTI/EXEC block to guarantee atomicity of the query in the following way:

do {
    WATCH value
    i = 1 + GET value
    MULTI
    set value i
    SADD set i
    result = EXEC
} while (result == nil)

answered Nov 30, 2011 at 1:53

seppo0010

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1 Comment

MarcosPri Over a year ago

Thanks! WATCH was the missing piece.

alecxe · Accepted Answer · 2013-12-08 19:54:03Z

0

There is a GETSET (http://redis.io/commands/getset) command for Redis where you can get the "old" value of a variable and set it to a new on the same command.

Almost certain that there is no method to incr a value and add it to a set because they are different data types for redis.

Hope it helps!

edited Dec 8, 2013 at 19:54

alecxe

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answered Nov 29, 2011 at 20:33

Gonzalo

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