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Erik Bruchez edited this page Sep 24, 2015 · 8 revisions

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Scenarios

Make a control read-only based on the value of another control

Scenario: Make a control read-only if the value of the first-name control is blank:

Expression:

normalize-space($first-name) = ''

Explanation:

  • $first-name returns the value of the control with name "first-name"
  • normalize-space() is a standard XPath function which removes all leading and trailing white space and combine internal white space. Using this function ensures that, even if the value contains spaces, it resolves to an empty string.
  • = '' compares the result of the function to the empty string

Setting a dynamic initial value

Scenario: As a form author, you can set a static initial value for a control simply by setting that value at design time. For example:

  • Enter a value in an input field
  • Select an item in a dropdown list

But not all initial values can be static. For example, you might want a date selection control to contain the current date until the user changes it. In this case, you can use an "Initial Value" expression.

Initial Value expression:

current-date()

Explanation:

  • current-date() is a standard XPath function returning the current date.

Simple calculated values

Scenario: compute the sum of two numbers entered by the user in two fields, "quantity1" and "quantity2".

Calculated Value expression:

if ($quantity1 castable as xs:integer and $quantity2 castable as xs:integer)
then $quantity1 + $quantity2
else ''

Explanation:

  • if (...) then ... else ... evaluates a condition and then returns one of two alternatives
  • the condition quantity1 castable as xs:integer checks that the value from the field "quantity1" is an integer
  • quantity1 + $quantity2 simply adds the two values
  • the value '' represents an empty string This can be specified for example on a Text Output control.

NOTE: If the value of a control is calculated, by default it is also marked as read-only. If you want a calculated control to be still editable by the user, set its Read-Only property explicitly to false().

Sum of values in a repeat

[SINCE Orbeon Forms 4.0]

Scenario: compute the sum of values in multiple repeat iterations.

Say you have:

  • a repeat called my-repeat
  • with a decimal field called number on each row

Calculated value expression:

sum($my-repeat/number[. castable as xs:decimal])

Explanation:

  • $my-repeat points to the repeat data's enclosing XML elements
  • the nested /number path points to the number field within each iteration
  • [. castable as xs:decimal] excludes values that are blank or not decimal number
  • sum() is a standard XPath function to compute the sum of a sequence of items

Access a control in a particular repeat iteration

Given this form and a control called name within a repeat:

  • $name[2]: return the value of the control in the second iteration
  • string-join($name, ', '): join all values with commas
  • count($name): return the number of values

NOTE: This works when the expression is outside repeat iterations. For expressions within the same repeat, $name returns the closest control.

See also Model bind variables and this StackOverflow question.

Check the role(s) of the current user

See Form Fields.

Check the Form Runner mode

A special XPath variable named $fr-mode is exposed by Form Runner to all XPath expressions. Its value can be one of:

  • new
  • edit
  • view
  • pdf
  • email

You can test the mode as follows, for example in a Visibility expression:

$fr-mode = 'edit'

Access HTTP request parameters and HTTP headers

It can be useful to access HTTP headers to set default values upon form initialization, for example when single sign-on systems use HTTP headers as a way of communicating information to an application.

XPath expressions have access to a special function, xxf:request-header(), which allows retrieving a header by name. Example of setting the default value of a field using an initial value:

xxf:get-request-header('full-name')

NOTE: With Orbeon Forms 3.8 and 3.9, headers cannot be reliably accessed after the form is initialized, so this function should be used for setting initial values on controls only. See the next scenario for a workaround.

Check the type of an attachment

Scenario: field my-attachment must be a PDF file.

Constraint expression:

ends-with(lower-case($my-attachment/@filename), '.pdf')

Explanation:

  • Form Runner stores information about a file into XML attributes:
    • @filename accesses the file name as sent by the user's browser
    • @mediatype accesses the file type as sent by the user's browser
    • @size accesses the file size
  • $my-attachment/@filename returns the file name associated with attachment "my-attachment"
  • The lower-case() function converts that name to a lower case value
  • The ends-with() function checks whether its first argument ends with the second argument

Similarly, you can test the file type:

$my-attachment/@mediatype = 'application/pdf'

NOTE: Because the file name and file type are sent by the client's browser, they cannot be trusted. This should only be considered a first level of data validation, and further validation based on the content must be performed at a later time if needed. See also issue #1838.

Validate the length of a value

Scenario: the maximum length of the "last-name" control is 30 characters.

Constraint expression:

string-length($last-name) <= 30

Explanation:

  • The standard string-length() function returns the length of its argument
  • The <= or lt comparator means "lower than or equal to"

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