This page summarises which variables are available in different contexts, and explains how to create and use $-variables. See also Expression Basics.
The following tables gives some guidelines for the availability of variables, based on the PhixFlow Timing Cycle for evaluating analysis models.
| Location of Expression | Available Variables |
|---|---|
| Input multiplier | Some internal variables e.g. _toDate $-variables declared locally in the input multiplier |
| Database collector SQL script | %USERNAME%, %PASSWORD% $-variables |
| Output Multiplier | internal variables e.g. _toDate $-variables |
| Attribute expression | internal variables e.g. _toDate All <pipeName> values e.g. inpipe.accountVal All _out.value where value is the name of the attribute and it is before the current attribute in the stream All user defined variables created in a prior attribute expression |
| Output filter expression | internal variables e.g. _toDate All _out.attribute values All user defined variables created in any Attribute expression |
| Pipe index expression on a lookup pipe | internal variables <pipename>.attribute - the name on an input pipe All _out.value where value is the name of the attribute and it is before the current attribute in the stream |
Variable Scoping
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When writing expressions that reference variables it is important to understand whether PhixFlow has "seen" the variable yet. This is the scope of the variable.
In a stream, output multiplier or output filter, the attributes have a specified order. When you run analysis on a model, PhixFlow processes each attribute in order, evaluating their expressions. This means you cannot reference:
- an attribute name before PhixFlow has processed it. So in the first attribute in a stream, you cannot use a value from the third attribute in the stream.
- a $-variable before PhixFlow has processed the expression where it is set.
You can only reference:
- an attribute name in a subsequent attribute
- a $-variable after it has been set or evaluated.
Internal Variables
PhixFlow has a list of Internal Variables. For example, some common ways to reference attributes in a stream:
| Variable | Syntax | Example | Details |
|---|---|---|---|
. | <pipe_name>.<attribute_name> | in.AppleHarvestDate | Indicates the source of the attribute is the incoming pipe. The default name for a pipe is "in". |
| _out | _ | _out.AppleHarvestDate | PhixFlow processes stream attributes in their specified order. _ |
| toDate | see toDate | if( _out.AppleHarvestDate < _toDate('20210101'), 1, 0) | In this case one of the arguments in an if statement is an internal variable, that indicates the date up-to which PhixFlow will process a record. |
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If your expression is not working, check the order of the stream attributes. Make sure anything the expression references has already been processed or evaluated by PhixFlow. If the expression is referencing something with a higher order number, PhixFlow has not processed it yet, so cannot find it. |
In applications, some commonly-used internal variables are
- _grid: to refer to a data grid in a stream view or layout.
- _form: to refer to a form on a layout.
- _context: to refer to a Context Parameter
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The internal variables that you can use in an expression depend on context. Remember to check the properties page for the item on which you are working; see Property TabsProperties, Windows, Menus and Toolbars. |
Creating and Using $-variables
Defining a $-variable
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PhixFlow assumes that you are declaring a variable and setting its value the first time it occurs in the expression.
$localVar = 'Smith' $GlobalVar = 'St.John-Smith'
Using $-Variables in Expressions
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In expressions that have complex calculations, you may need a variable to hold the result of a calculation. You can then reference the variable later in the expression, or in other attribute expressions for the same stream. The following expression uses do() function and $-variables for a simple calculation.
When to Use $-variables$-variables are not really needed in simple calculations. They are useful:
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Using $-variables Throughout an Application
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$-variables can have different "scope". They can be:
- only used withn an expression or within a stream attribute.
- used more widely, in multiple expressions or for different stream attributes.
Although the variables are the same, to distinguish between these two usages we use the terms local and global respectively.
There are some situations where you want to set a $-variable to use throughout your application. For example:
- Users can access your application on a desktop or mobile platform. The form-factor affects which styles you want want to use to display the application.
Also see Using Size and Position for Responsive Design/wiki/spaces/HELP100/pages/9106729471. - You application is used by people in different countries. This could affect different aspects of the application, such as showing the relevant flag on a dashboard.
Also see Translating an Application Interface.
In both these examples, you want to reference a $-variable that identifies the device or country. You then use the $-variable to select an appropriate formatting rule to customise the application's appearance.
To make a $-variable available throughout the application, you need to set it on something that always happens and is then always available. You can acheive this by:
- Setting a $-variable as a context parameter on the application's open action.
- Linking the context parameter it to something on the first screen that opens, such as the application home screen.
The steps in more detail are:
- In the repository, find the action that opens the application. In its properties, add a Context Parameter; see Table-Action.
- In the context parameter's Expression field, set the $-variable; see Context Parameter.
- In the repository, find the application's first screen. Right-click and select Display. On the dashboard:
- From the palette drag in a simple form field onto an area.
For example, use the palette Basic Components →StringField. A field is a type of layout component; see LayoutComponent. - Give the field exactly the same as the context parameter.
- In the field properties tab, at the end of the Style Settings section, tick Hidden.
- From the palette drag in a simple form field onto an area.
- To display the dashboard property tab, right-click to display the context menu. Select Show Dashboard Details or Dashboard Options → Show Details.
- In the properties tab Basic Settings section, tick Keep Data.
You have now created a $-variable that PhixFlow always knows about, but which is not visible to users. To reference this variable in any expression or script, use:
<dashboard>.<field>
For example, if the dashboard is called HomePage, and the field is called Mobile, you would reference HomePage.Mobile. The field name effectively redirects PhixFlow to the context parameter where the $-variable is set.
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If you need to find the name of something on a dashboard, right-click on the component and select Show Element. PhixFlow opens the properties tab for the component. |
Variable Typing
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When a variable is first used, PhixFlow makes a best guess about what type of data is stored in that variable; see Parameter Types. For example:
| Expression | PhixFlow identifies data type |
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$thisNumber = 4 | integer |
$thisAddress = '123 Fake St' | string |
$thisNumber = $thisAddress
The cases where you may be able to change a data type are
- integer to a floating point value: PhixFlow may be able to convert between these.
- by using type conversion function, such as toDate. This forces a value of one type into a variable of another type.