Sets an attribute value by following a reference from one attribute to another, where the first attribute contains the name of the desired (second) attribute. The referenced value is retrieved and assigned to a new attribute.
Typical Uses
- Carry out a join where there is no join key, but one attribute is a pointer to the required value
How does it work?
The AttributeDereferencer receives the name of an attribute in the Source Attribute parameter. The Source Attribute’s value references (is the name of) another attribute, and the value of this secondary attribute will be added to a newly created Destination Attribute.
Example: Using the AttributeDereferencer with a User Parameter
In this example, we start with a simple tabular dataset of Ice Cream sales numbers for a year.
To extract the sales numbers for any given month, we create a simple workspace that contains a User Parameter called Month. It has been configured as a Choice parameter, and the possible Month values provided. Upon running the workspace (with Prompt), the user selects the month “Jul”, which becomes the current value assigned to the Month parameter.
In the workspace, the features are routed through a ParameterFetcher and then on to the AttributeDereferencer.
In the ParameterFetcher, the Month parameter’s value - “Jul” - is assigned to a new attribute named _Month.
Then, in the AttributeDereferencer, the Source Attribute is _Month, and the newly created Destination Attribute has the default name _dereferenced.
The output features now have a _dereferenced attribute, the contents of which are determined by the User Parameter choice - in this case, “Jul”.
Configuration
Input Ports
Input
Features with attributes.
Output Ports
Output
Features with a copy of the value of the referenced source attribute.
Parameters
Parameters
| Source Attribute | The attribute containing a reference to another attribute. |
| Destination Attribute | The new attribute that will contain a copy of the referenced value. |
Editing Transformer Parameters
Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click 
beside the applicable parameter. For more information, see Transformer Parameter Menu Options.
Defining Values
There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters. There are a number of tools and shortcuts that can assist in constructing values, generally available from the drop-down context menu adjacent to the value field.
How to Set Parameter Values
Using the Text Editor
The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.
Using the Arithmetic Editor
The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.
Conditional Values
Set values depending on one or more test conditions that either pass or fail.
Parameter Condition Definition Dialog
Content
Expressions and strings can include a number of functions, characters, parameters, and more - whether entered directly in a parameter or constructed using one of the editors.
Content Types
| These functions manipulate and format strings. | |
| A set of control characters is available in the Text Editor. | |
| Math functions are available in both editors. | |
| These operators are available in the Arithmetic Editor. | |
| These return primarily feature-specific values. | |
| FME and workspace-specific parameters may be used. | |
| Working with User Parameters | Create your own editable parameters. |
Reference
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Processing Behavior |
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Feature Holding |
No |
| Dependencies | None |
| FME Licensing Level | FME Base Edition and above |
| Aliases | |
| History | |
| Categories |
FME Knowledge Center
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Examples may contain information licensed under the Open Government Licence – Vancouver