Expressions (beta)

App spec expressions functionality is in beta testing and may be subject to change.
An expression is a special form of an attribute value. It is dynamically executed in the context of other fields and variables. A return value of the expression determines the value of the attribute.
Currently, expressions can be applied to the following attributes of the field:
​"Visible" field attribute​
​"Mandatory" field attribute​
Expressions can include field paths, variables, literals, operators. Expressions can be nested and can include other expressions.
Field paths
A field path can be used to access other field values within the expression. The path can be absolute or relative to the current execution scope.
Absolute path
An absolute field path is specified with the following form:
 "$$<GLOBAL_SCOPE>.<field_key>"
Available global scopes for project fields:
$$PROJECT_FIELDS - contains values for all app setup fields of the project.
Available global scopes for event fields:
$$PROJECT_FIELDS - contains values for all app setup fields of the project.
$$EVENT_FIELDS - contains values for all event settings fields of the event.
Available global scopes for element fields:
$$PROJECT_FIELDS - contains values for all app setup fields of the project.
$$EVENT_FIELDS - contains values for all event settings fields of the event.
$$ELEMENT_FIELDS - contains values for all element custom fields of the element.
Available global scopes for question fields:
$$PROJECT_FIELDS - contains values for all app setup fields of the project.
$$EVENT_FIELDS - contains values for all event settings fields of the event.
$$ELEMENT_FIELDS - contains values for all element custom fields of the element.
$$QUESTION_FIELDS - contains values for all question fields of the element.
Available global scopes for option fields:
$$PROJECT_FIELDS - contains values for all app setup fields of the project.
$$EVENT_FIELDS - contains values for all event settings fields of the event.
$$ELEMENT_FIELDS - contains values for all element custom fields of the element.
$$QUESTION_FIELDS - contains values for all question fields of the element.
$$OPTION_FIELDS - contains values for all option fields of the element.
Examples of absolute field paths:
"$$PROJECT_FIELDS.appMode"
"$$PROJECT_FIELDS.footerEnabled"
"$$EVENT_FIELDS.IosVersion"
Relative path
A relative field path has the following form:
"$<field_key>"
The path is automatically resolved to the scope of expression execution. For example, if the expression is used on a top-level app setup field, the relative path "$appMode" is an equivalent of the absolute path "$$PROJECT_FIELDS.appMode".
Besides global scopes, there is also a collection item implicit scope. If an expression is used on a field in a collection item, relative field paths are resolved to fields of the same collection item.
Examples of relative field paths:
"$slideDisplayMode"
"$itemDisabled"
Field types and return values
Not all fields can be directly referenced with a field path.
Currently supported field types are:
Field type
Returned value type
freetext
string
list
string
boolean
boolean
number
number
For fields that support localisation, the value of the default locale is returned.
Variables
A variable can be specified to access project's related values within the expression. The variable can be absolute to the current execution scope only.
A variable contains a value of a specific type and is specified with the following form: 
"$$<VARIABLE_PATH>"
Variable can be nested. In that case, variable path contains . as a separator.
Built-in variables
The following built-in variables are defined:
$$PROJECT_ELEMENTS - an object containing project element attributes grouped by element's content_type. An attribute can be accessed with the following syntax:
"$$PROJECT_ELEMENTS.<element_content_type>.<attribute>"
Attribute
Type
Description
 visible
boolean
Return true if element is enabled on Project Settings -> Elements 
Example: 
mandatory": { 
  "$eq": ["$$PROJECT_ELEMENTS.rpoll-custom.visible", false] 
}
Literals
Literals are static values that can be used in comparison expressions.
Literal type
Examples
Text
number
123
3.14
​
string
"some string"
​
boolean
true
false
​
Operators
An expression operator has the following form:
"<operator>": [<argument1>, <argument2>...]
The argument of an operator is another expression - literal, operator, field path etc.
Operator
Description
Arguments
Return value
$eq
Checks if all arguments are equal
Count: 2+
All arguments must be of the same type.
boolean
$ne
Checks if any argument is not equal to others
Count: 2+
All arguments must be of the same type.
boolean
$or
Checks if any argument is true
Count: 2+
All arguments must be of a boolean type.
boolean
$and
Checks if all arguments are true
Count: 2+
All arguments must be of a boolean type.
boolean
Examples
A field is mandatory if language_selector_position field has value "left".
"mandatory": { 
  "$eq": ["$$PROJECT_FIELDS.language_selector_position", "left"] 
}
​
A field is visible if banner_left_enabled has value true or banner_right_enabled has value true. In other words, a field is visible if at least one of the boolean fields is true.
"visible": {
  "$or": [
    { "$eq": ["$$PROJECT_FIELDS.banner_left_enabled", true] },
    { "$eq": ["$$PROJECT_FIELDS.banner_right_enabled", true] },
    { "$eq": ["$$PROJECT_ELEMENTS.rpoll-custom", true] }
  ]
}
​
A field is mandatory in a collection item if has_title field of the same collection item is true.
"mandatory": {
  "$eq": ["$has_title", true]
}
​
A field is visible if poll element is enabled in Project Settings.
"visible": { 
  "$eq": ["$$PROJECT_ELEMENTS.poll.visible", true] 
}

Field type	Returned value type
`freetext`	`string`
`list`	`string`
`boolean`	`boolean`
`number`	`number`

Attribute	Type	Description
`visible`	`boolean`	Return `true` if element is enabled on Project Settings -> Elements

Literal type	Examples	Text
number	`123` `3.14`
string	`"some string"`
boolean	`true` `false`

Operator	Description	Arguments	Return value
`$eq`	Checks if all arguments are equal	Count: 2+ All arguments must be of the same type.	`boolean`
`$ne`	Checks if any argument is not equal to others	Count: 2+ All arguments must be of the same type.	`boolean`
`$or`	Checks if any argument is `true`	Count: 2+ All arguments must be of a boolean type.	`boolean`
`$and`	Checks if all arguments are `true`	Count: 2+ All arguments must be of a boolean type.	`boolean`

Project settings spec (Experience Setup)

Data Sources (beta)

Last modified 8mo ago