Introduction

Back end expressions are a tool to get or set variables during the execution of processes, cases, or decision tables. Back end expressions can also be used to implement custom logic or to delegate that logic to a Java service deployed on the server. Examples of using expressions usage are setting dynamic task names, evaluation of sequence flows after a gateway, or create a variable of a certain type. As the name implies, these expressions run on the back end, during execution. As such they have no access to the frontend data at the time of evaluation.

In Flowable Design, expressions are allowed in fields marked with a lightning bolt: .

Flowable uses the Unified Expression Language (UEL) for resolving expressions. The documentation for UEL is a good reference for syntax and available operators. Each expression starts with ${ and ends with }.

There are two types of expressions:

• value expressions provide a value. Supported values include Boolean, string, integer, floating-point number, and null. A typical value expression is ${variable.property} or ${bean.property}.

• method expressions invoke a method with or without parameters. An example of method expression is ${bean.setPropertyValue('newValue')}. To distinguish between a value expression and a method expression without any parameters, use empty parentheses at the end of the method call. For example, ${variable.toString()}.

In theory, any Spring bean exposed to the application is available for use in backend expression, but not all classes can be serialized in a way which will allow for a proper expression evaluation.

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Certain expressions are available in scripts (e.g. for use in a BPMN or CMMN script task). A list of expressions which can be used is available as part of the backend scripting documentation.

Keywords

The process and CMMN engines support context-dependent objects. Both engines resolve hierarchy objects like root and parent and can be used to access their local properties. root stands for the object on the top of the execution hierarchy, which can be a process instance or case instance. parent is a reference to the first process or case instance immediately above the current object in the hierarchy.

For process instances and case instances definition grants access to the definition and all its attributes.

In the context of BPMN execution, additional reserved keywords are execution and authenticatedUserId.

• execution references to the current 'path of execution' or 'token'. It provides access to properties like name, businessKey, processDefinitionId, and parentExecution (technically, it is backed by the ExecutionEntity class).

• task is a reference to the current task (technically, it is backed by the TaskEntity class).

• authenticatedUserId is a string identifier of the currently authenticated user. If there is no authenticated user, the variable is not available.

The CMMN engine context supports task (see above), caseInstance, and planItemInstance.

• caseInstance references to the current case instances. It provides access to properties like name, state, businessKey, caseDefinitionId, and parentId (technically, it is backed by the CaseInstanceEntity class).

• planItemInstance references the plan item instance associated with the case.

When a process or case instance is deployed within a Flowable app, the flowApp keyword is available in both BPMN and CMMN contexts.

• flowApp provides access to app-level variables (e.g. ${flowApp.customerName}) and to the app definition via ${flowApp.definition} (e.g. ${flowApp.definition.key}). See App Expressions for more details.

Reserved Variable Names

Flowable reserves a number of names at the task, process, case, and expression layers. Using any of these as a custom variable name can lead to unexpected results. The lists below are a non-exhaustive set of names to avoid when defining custom variables.

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For form related list of reserved words see the Form Editor reference — Binding.

Task Properties

Variable	Task property
id	Task ID
name	Task name
description	Task description
state	Task state
owner	Task owner
assignee	Current task assignee
delegationState	Task delegation state (PENDING / RESOLVED)
priority	Task priority
category	Optional tag classifying the task
formKey	Form reference for the task
dueDate	Task due date
suspended	Whether the task is suspended
createTime	Task creation time
startTime	Task start time
endTime	Task end time
claimTime	Time the task was claimed
claimedBy	User who claimed the task
completedBy	User who completed the task
inProgressStartTime	Date/time when the task was put in progress
inProgressStartedBy	User who put the task in progress
inProgressStartDueDate	Due date while the task is in progress
parentTaskId	Parent task ID for sub-tasks
parentTaskName	Parent task name
executionId	Execution ID owning the task
processInstanceId	Process instance ID
processInstanceName	Process instance name
processDefinitionId	Process definition ID
processDefinitionName	Process definition name
processDefinitionCategory	Process definition category
caseInstanceName	Case instance name
caseDefinitionName	Case definition name
caseDefinitionCategory	Case definition category
taskDefinitionId	Task definition ID
taskDefinitionKey	ID of the activity in the process defining this task
scopeId	Scope ID
subScopeId	Sub-scope ID
scopeType	Scope type (bpmn, cmmn, etc.)
scopeDefinitionId	Scope definition ID
tenantId	Tenant ID
permissions	Permissions for the current user
translations	Translation values

Process Instance Properties

Variable	Description
id	Execution ID
processInstanceId	Process instance ID
name	Process instance name
businessKey	Process business key
businessStatus	Business status
businessStatusLabel	Translated business status label
suspended	Whether the process instance is suspended
suspensionState	Suspension state
isActive	Whether the execution is currently active
ended	Whether the process instance has ended
completed	Whether the process instance has completed
activityId	Current activity ID
startActivityId	Starting activity ID
startTime	Process start time
endTime	Process end time
startUserId	User who started the process
assignee	Process assignee
owner	Process owner
dueDate	Process due date
claimTime	Time the process was claimed
claimedBy	User who claimed the process
callbackId	Callback ID
callbackType	Callback type
referenceId	Reference ID
referenceType	Reference type
parentId	Parent execution ID
superExecutionId	Super execution ID for call activities
rootProcessInstanceId	Root process instance ID
propagatedStageInstanceId	CMMN parent stage instance ID for executions inside a case stage
processDefinitionId	Process definition ID
processDefinitionKey	Process definition key
processDefinitionName	Process definition name
processDefinitionDescription	Process definition description
processDefinitionCategory	Process definition category
processDefinitionVersion	Process definition version
processDefinitionDeploymentId	Process definition deployment ID
deploymentId	Deployment ID
tenantId	Tenant ID
permissions	Permissions for the current user
translations	Translation values

Case Instance Properties

Variable	Description
id	Case instance ID
name	Case instance name
businessKey	Case business key
businessStatus	Business status
businessStatusLabel	Translated business status label
parentId	Parent case instance ID
state	Case instance state
completed	Whether the case has completed
completeable	Whether the case can complete
started	Time the case started
startTime	Case start time
ended	Time the case ended
startUserId	User who started the case
startedByUserId	User who started the case
lastReactivationTime	Last time the case was reactivated
lastReactivationUserId	User who last reactivated the case
assignee	Case assignee
owner	Case owner
dueDate	Case due date
claimTime	Time the case was claimed
claimedBy	User who claimed the case
customViewKey	Custom view key
agentInstanceId	Agent instance ID
callbackId	Callback ID
callbackType	Callback type
referenceId	Reference ID
referenceType	Reference type
caseDefinitionId	Case definition ID
caseDefinitionKey	Case definition key
caseDefinitionName	Case definition name
caseDefinitionDescription	Case definition description
caseDefinitionCategory	Case definition category
caseDefinitionVersion	Case definition version
caseDefinitionDeploymentId	Case definition deployment ID
tenantId	Tenant ID
permissions	Permissions for the current user
translations	Translation values

Multi-Instance Loop Variables

A BPMN multi-instance activity automatically sets the following variables.

Variable	Description
nrOfInstances	Total number of instances in the loop, set on the multi-instance root execution
nrOfActiveInstances	Number of currently active instances, set on the multi-instance root execution
nrOfCompletedInstances	Number of completed instances, set on the multi-instance root execution
loopCounter	Index of the current iteration, set as a local variable on each child execution

The default loopCounter name can be overridden per activity via the elementIndexVariable attribute on the multi-instance loop characteristics.

Reserved Internal Prefixes

Flowable reserves variable names starting with __flowable or __flw for engine-internal use, and may add further internal names under these prefixes in future releases without notice.