[[transform]]
=== Transform

A _transform_ processes the payload in the watch execution context to prepare the payload for  watch actions. 

NOTE: If no transforms are defined, the actions have access to the payload as loaded by the watch input. 

You can define transforms in two places:

1.  As a top level construct in the watch definition. In this case, the payload is
    transformed before any of the watch actions are executed.

2.  As part of the definition of a particular action. In this case, the payload is 
    transformed before that action is executed. The transformation is only applied to the payload for that specific action.

If all actions require the same view of the payload, define a transform as part of the watch definition. If each action requires a different view of the payload, define different
transforms as part of the action definitions so each action has the payload prepared by its own dedicated transform.

The following example defines two transforms, one at the watch level and one as part of the definition of the `my_webhook` action.

[source,json]
.Watch Transform Constructs
--------------------------------------------------
{
  "trigger" : { ...}
  "input" : { ... },
  "condition" : { ... },
  "transform" : { <1>
    "search" : {
      "body" : { "query" : { "match_all" : {} } }
    }
  }
  "actions" : {
    "my_webhook": {
      "transform" : { <2>
      	"script" : "return ctx.payload.hits"
      }
      "webhook" : {
      	"host" : "host.domain",
      	"port" : 8089,
      	"path" : "/notify/{{ctx.watch_id}}"
      }
    }
  ]
  ...
}
--------------------------------------------------

<1> A watch level `transform`
<2> An action level `transform`

Watcher supports three types of transforms: <<transform-search, `search`>>, <<transform-script, `script`>>
and <<transform-chain, `chain`>>.

include::transform/search.asciidoc[]

include::transform/script.asciidoc[]

include::transform/chain.asciidoc[]