You can use subworkflows to define a piece of logic or a set of steps you want to call multiple times, simplifying the workflow definition. Subworkflows are similar to a function or routine in a programming language. They can accept parameters and return values, allowing you to create more complex workflows with a broader range of applications.
For information on basic workflow tasks, see Create and update an existing workflow and Execute a workflow .
Main block
If a workflow has a subworkflow, the main workflow must be placed in a main
block. Subworkflows are always defined after the main body of the workflow
definition:
YAML
main : steps : - STEP_NAME : ... ... SUBWORKFLOW_NAME : params : [ PARAMETER_1 , PARAMETER_2... ] steps : - SUBWORKFLOW_STEP_NAME : ...
JSON
{ "main" : { "steps" : [ { " STEP_NAME " : ... } ... ] }, " SUBWORKFLOW_NAME " : { "params" : " [PARAMETER_1 , PARAMETER_2...] " , "steps" : [ { " SUBWORKFLOW_STEP_NAME " : ... } ] } }
If you don't need to pass parameters to the subworkflow, delete the params
block. Note that any parameters must be enclosed in square brackets. For example:
params: [Street, ZipCode, Country]
Note that the steps
block is required inside a SUBWORKFLOW_NAME
block. It can contain the following:
Default parameters in subworkflows
Subworkflows support default values for parameters. The default parameter value is used only if a parameter isn't provided as part of a subworkflow call.
YAML
SUBWORKFLOW_NAME : params : [ PARAMETER_1 , PARAMETER_2 : DEFAULT_VALUE2... ] steps : - SUBWORKFLOW_STEP_NAME : ...
JSON
{ " SUBWORKFLOW_NAME " : { "params" : " [PARAMETER_1 , PARAMETER_2 : DEFAULT_VALUE2...] " , "steps" : [ { " SUBWORKFLOW_STEP_NAME " : ... } ] } }
For example, the following workflow can be called with or without a Country parameter, and if the Country is not specified, it defaults to "United States".
YAML
build_address : params : [ Street , ZipCode , Country : "United States" ] steps : - concatenate : return : ${Street + ", " + ZipCode + ", " + Country}
JSON
{ "build_address" : { "params" : [ "Street" , "ZipCode" , { "Country" : "United States" } ], "steps" : [ { "concatenate" : { "return" : "${Street + \", \" + ZipCode + \", \" + Country}" } } ] } }
Call a subworkflow
You call a subworkflow using the call
field within a workflow step in the main
workflow, optionally supplying arguments to pass to the subworkflow:
YAML
main : steps : - STEP_NAME : call : SUBWORKFLOW_NAME args : ARG_1 : VALUE_1 ARG_2 : VALUE_2 ... result : OUTPUT_VARIABLE SUBWORKFLOW_NAME : params : [ PARAMETER_1 , PARAMETER_2 ... ] steps : - step_1 : ...
JSON
{ "main" : { "steps" : [ { " STEP_NAME " : { "call" : " SUBWORKFLOW_NAME " , "args" : { " ARG_1 " : " VALUE_1 " , " ARG_2 " : " VALUE_2 " }, "result" : " OUTPUT_VARIABLE " } } ] }, " SUBWORKFLOW_NAME " : { "params" : [ " PARAMETER_1 , PARAMETER_2 " ... ], "steps" : [ { "step_1" : ... } ] } }
If the subworkflow accepts parameters, you can pass arguments ( ARG_1
, ARG_2
) and their values ( VALUE_1
, VALUE_2
) to the workflow. If the subworkflow returns
anything, you can store the data in the OUTPUT_VARIABLE
.
This example defines a subworkflow named name_message
and calls it from the
main workflow:
YAML
main : steps : - call_subworkflow : call : name_message args : first_name : "Ada" last_name : "Lovelace" result : output - call_subworkflow2 : call : name_message args : first_name : "Sherlock" last_name : "Holmes" result : output2 - return_message : return : ${output + " " + output2} name_message : params : [ first_name , last_name , country : "England" ] steps : - prepareMessage : return : ${"Hello " + first_name + " " + last_name + " from " + country + "."}
JSON
{ "main" : { "steps" : [ { "call_subworkflow" : { "call" : "name_message" , "args" : { "first_name" : "Ada" , "last_name" : "Lovelace" }, "result" : "output" } }, { "call_subworkflow2" : { "call" : "name_message" , "args" : { "first_name" : "Sherlock" , "last_name" : "Holmes" }, "result" : "output2" } }, { "return_message" : { "return" : "${output + \" \" + output2}" } } ] }, "name_message" : { "params" : [ "first_name" , "last_name" , { "country" : "England" } ], "steps" : [ { "prepareMessage" : { "return" : "${\"Hello \" + first_name + \" \" + last_name + \" from \" + country + \".\"}" } } ] } }
This workflow definition does the following:
- The main workflow calls the
name_messagesubworkflow twice, from the stepscall_subworkflowandcall_subworkflow2. - The two steps supply different inputs for the arguments
first_nameandlast_name, which are then passed to the subworkflow. - The subworkflow
name_messagetakes the arguments passed to it and constructs a simple message, supplying the default value ofEnglandfor thecountryvariable. - The subworkflow returns the message it constructs to the main workflow.
- The steps in the main workflow store the results as
outputandoutput2, respectively. - The main workflow combines
outputandoutput2into a single message and returns the result:Hello Ada Lovelace from England. Hello Sherlock Holmes from England.
For more information, see Calls .
Call a subworkflow in an expression
This example is identical to the preceding example except that the workflow calls the subworkflow using an expression . Note that expressions cannot contain calls to subworkflows with blocking steps.
YAML
main : steps : - call_subworkflow : assign : - output : ${name_message("Ada","Lovelace")} - call_subworkflow2 : assign : - output2 : ${name_message("Sherlock","Holmes")} - return_message : return : ${output + " " + output2} name_message : params : [ first_name , last_name , country : "England" ] steps : - prepareMessage : return : ${"Hello " + first_name + " " + last_name + " from " + country + "."}
JSON
{ "main" : { "steps" : [ { "call_subworkflow" : { "assign" : [ { "output" : "${name_message(\"Ada\",\"Lovelace\")}" } ] } }, { "call_subworkflow2" : { "assign" : [ { "output2" : "${name_message(\"Sherlock\",\"Holmes\")}" } ] } }, { "return_message" : { "return" : "${output + \" \" + output2}" } } ] }, "name_message" : { "params" : [ "first_name" , "last_name" , { "country" : "England" } ], "steps" : [ { "prepareMessage" : { "return" : "${\"Hello \" + first_name + \" \" + last_name + \" from \" + country + \".\"}" } } ] } }
Simple subworkflow
This sample implements a simple subworkflow. When a workflow has a subworkflow,
the main workflow must be placed in a main
block. Subworkflows are always
defined after the main body of the workflow definition.
