CenterView Variables

Introduction

CenterView has 3 different kinds of Variable which can be referenced in Attribute Expressions and other places where expressions are allowed. These are :

• Internal Variables - These are variables that are created and populated by CenterView when certain actions happen. E.g. _fileName is populated by CenterView and is available in the definition of Stream attribute, when the streamset has data that is coming from a fileCollector. A full list of Internal Variables, and how they are populated can be found here.
• User Defined Variables - These are variables that are defined by the user, and can be used to hold data required for complex calculations in attributes or other expressions.
• Attribute Names - These are the attribute names that are defined as part of a Stream which are subsequently available for use in other attributes or expressions. Attributes can referred to in File Collectors, and implicit attribute names come from database collectors as a special case where these are the names of the fields returned by the DB Collector query. Attribute names can be qualified with pipe names e.g. pipename.recordID.

Defining a Variable

A User Defined Variable must start with the $ character. By convention, Camel case naming convention is used (Camel case is a convention where names are made up of multiple words, with no spaces and the first letter of each word is capitalised. e.g. ThisIsCamelCase) when giving a variable a name, and variables that are local to the current function or expression should start with a lower case letter after the initial $ character. Variables whose scope extends beyond the current attribute expressions should start with an upper case letter after the initial $ character.

A User Defined variable need not be declared. The first time a variable is referred to in an expression, it is assumed that the variable is being declared and a value is being assigned to it.

$localVar = 'Smith' $GlobalVar = 'St.John-Smith'

Variable Typing

When a variable is first used, CenterView will make a best guess about what type of data is stored in that variable. e.g.

$thisNumber = 4 // A Number $thisAddress = '123 Fake St' // A String Value

When CenterView has decided what type of data is stored in a variable, that type will not change. So in the above example,

$thisNumber = $thisAddress

will cause CenterView 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, Centerview 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.

Variable Scoping

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 CenterView Timing Cycle for evaluating Models.

See Also

• Scripting
• Internal Variables