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Data in a data store can be updated through two different paths. The first is by giving a key-value pair for a domain by raising wrangler:ds_update and then responding to wrangler:ds_updated. The second is by changing all the key-value mappings under a domain by raising wrangler:ds_assign_map_to_domain with a new key-value map and reacting to wrangler:ds_domain_updated. It is recommended to use the latter way of updating sparingly, such as for data migration purposes.
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/* An example of a rule that increments a counter value in the datastore */
rule incrementDS {
select when test incrementDS
pre {
currentCounter = datastore:getItem(meta:rid, "counter")o.picolabs.wrangler.profile that selects on the initialization of the datastore
newValue = currentCounter.isnull() => 0 | currentCounter + 1
}
always {
raise wrangler event "ds_update" attributes {
"domain":meta:rid, // The domain of the key-value pairings you want to manipulate
"key":"counter", // The key of the value you want to change
"value":newValue // The new value for the store
}
}
}
/* This rule reacts to wrangler:ds_updated to ensure that the counter we are incrementing
above is always even by checking if the new value in the store is divisible by 2 */
rule makeCounterEven {
select when wrangler ds_updated
pre {
domain = event:attr("domain")
key = event:attr("key")
value = event:attr("value")
}
if domain == meta:rid && key == "counter" && value % 2 == 1 then
noop()
fired {
raise wrangler event "ds_update" attributes event:attrs.put("value", value + 1)
}
} |
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