Accessing execution data from the Context object in Step Functions
Managing state and transforming data
Step Functions recently added variables and JSONata to manage state and transform data.
Learn about Passing data with variables and Transforming data with JSONata.
The Context object is an internal JSON structure that is available during an execution,
and contains information about your state machine and execution. The context provides your
workflows information about their specific execution. Your workflows can reference the
Context object in a JSONata expression with $states.context
.
Accessing the Context object
To access the Context object in JSONata
To access the Context object in JSONata states, use $states.context
in a
JSONata expression.
{
"ExecutionID", "{% states.context.Execution.Id %}"
}
To access the Context object in JSONPath
To access the Context object in JSONPath, you first append .$
to the end of
the key to indicate the value is a path. Then, prepend the value with $$.
to select a node in the Context object.
{
"ExecutionID.$": "$$.Execution.Id"
}
JSONPath states can refer to the context ($$.
) from the following JSONPath
fields:
-
InputPath
-
OutputPath
-
ItemsPath
(in Map states) -
Variable
(in Choice states) -
ResultSelector
-
Parameters
-
Variable to variable comparison operators
Context object fields
The Context object includes information about the state machine, state, execution, and task. This JSON object includes nodes for each type of data, and is in the following format.
{
"Execution": {
"Id": "String
",
"Input": {},
"Name": "String
",
"RoleArn": "String
",
"StartTime": "Format: ISO 8601
",
"RedriveCount": Number
,
"RedriveTime": "Format: ISO 8601
"
},
"State": {
"EnteredTime": "Format: ISO 8601
",
"Name": "String
",
"RetryCount": Number
},
"StateMachine": {
"Id": "String
",
"Name": "String
"
},
"Task": {
"Token": "String
"
}
}
During an execution, the Context object is populated with relevant data.
RedriveTime
Context object is only available if you've
redriven an execution. If you've redriven a Map Run, the RedriveTime
context
object is only available for child workflows of type Standard. For a
redriven Map Run with child workflows of type Express,
RedriveTime
isn't available.
Content from a running execution includes specifics in the following format.
{
"Execution": {
"Id": "arn:aws-cn:states:us-east-1:123456789012:execution:stateMachineName:executionName",
"Input": {
"key": "value"
},
"Name": "executionName",
"RoleArn": "arn:aws-cn:iam::123456789012:role...",
"StartTime": "2019-03-26T20:14:13.192Z"
},
"State": {
"EnteredTime": "2019-03-26T20:14:13.192Z",
"Name": "Test",
"RetryCount": 3
},
"StateMachine": {
"Id": "arn:aws-cn:states:us-east-1:123456789012:stateMachine:stateMachineName",
"Name": "stateMachineName"
},
"Task": {
"Token": "h7XRiCdLtd/83p1E0dMccoxlzFhglsdkzpK9mBVKZsp7d9yrT1W"
}
}
Note
For Context object data related to Map
states, see Context object data for Map states.
Context object data for Map states
Managing state and transforming data
Step Functions recently added variables and JSONata to manage state and transform data.
Learn about Passing data with variables and Transforming data with JSONata.
There are two additional items available in the Context object when processing a Map state: Index
and Value
. For each Map
state iteration, Index
contains the index number for the array item that is being currently processed, while
Value
contains the array item being processed. Within a Map
state, the Context object includes the following data:
"Map": {
"Item": {
"Index": Number
,
"Value": "String
"
}
}
These are available only in a Map
state, and can be specified in the ItemSelector (Map)
field.
Note
You must define parameters from the Context object in the ItemSelector
block of the main Map
state, not within the states included in the
ItemProcessor
section.
Given a state machine using a JSONPath Map
state, you can inject information
from the Context object as follows.
{ "StartAt": "ExampleMapState", "States": { "ExampleMapState": { "Type": "Map", "ItemSelector": { "ContextIndex.$": "$$.Map.Item.Index", "ContextValue.$": "$$.Map.Item.Value" }, "ItemProcessor": { "ProcessorConfig": { "Mode": "INLINE" }, "StartAt": "TestPass", "States": { "TestPass": { "Type": "Pass", "End": true } } }, "End": true } } }
If you execute the previous state machine with the following input, Index
and Value
are inserted in the output.
[ { "who": "bob" }, { "who": "meg" }, { "who": "joe" } ]
The output for the execution returns the values of Index
and Value
items for each of the three iterations as follows:
[
{
"ContextIndex": 0,
"ContextValue": {
"who": "bob"
}
},
{
"ContextIndex": 1,
"ContextValue": {
"who": "meg"
}
},
{
"ContextIndex": 2,
"ContextValue": {
"who": "joe"
}
}
]