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This page summarises which variables are available in different contexts, and explains how to create and use $-variables. See also Expression Basics.
Which Variables are Available
The following tables gives some guidelines for the availability of variables, based on the PhixFlow Timing Cycle for evaluating Models.
| Location of Expression | Available Variables |
|---|---|
| Input multiplier | Some internal variables (e.g. _toDate) $-variables (i.e. 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 |
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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.
Creating and Using $-variables
Defining a $-variable
A $-variable must start with the $ character. We recommend you use a consistent style for $-variable names.
- To distinguish between $-variables that are:
- only used in the current attribute, the inital character is lower case, for example
$percent - also used in another attribute, the initial character is capitalised, for example
$Percent.
- only used in the current attribute, the inital character is lower case, for example
- For multi-word names, use no spaces and camel case, for example
$ThisIsCamelCase
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 |
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. The following expression uses do() function and $-variables for a simple calculation.
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When to Use $-variables$-variables are not really needed in simple calculations. They are useful:
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Variable Typing
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When a variable is first used, PhixFlow
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makes a best guess about what type of data is stored in that variable
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; see Parameter Types. For example:
| Expression | PhixFlow identifies data type |
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$thisNumber = 4 |
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| integer | |
$thisAddress = '123 Fake St' |
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| string |
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you usually cannot change the type. PhixFlow will reject an expression that equates different types, such as:
$thisNumber = $thisAddress
will cause PhixFlow to reject the expression you are building. In some cases a type conversion function (e.g. toDate) can be used to force a value of one type, into a variable of another type.Note : in some cases, PhixFlow will be able to convert from one type to another. e.g. from an integer to a floating point value.
A further discussion of type assignments and full list of types is available in the Parameter Types section on the help page for Scripting Basics and a discussion on how complex expressions can be defined for attributes is available here.
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When writing expressions that reference variables it is important to understand the scope of those variables.
A Variable (or an Attribute Name) can only be referenced in an Expression if that Variable has already had a value assigned to it.
Note : Attributes are evaluated in order, so Variables defined in an Attribute (or the attribute name itself) can be referenced in a later Attribute Expression, or in a dependent Expression that is referenced after that Attribute is evaluated.
E.g. you can refer in a pipe index Expression to a $variable if you have done a "lookup($variable)" in the Stream before that pipe reference (or in an Output Multiplier, or an Output Filter), but otherwise you can’t.
The following tables gives some guidelines for the availability of Variables, based on the PhixFlow Timing Cycle for evaluating Models.
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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.