====== Expression Generator ======


===== About =====
A ''expression generator'' is a [[column|column data generator]] that can [[generator|generate]] data created from:
  * other columns (known as ''parent columns'') 
  * by giving an ''expression (or formula)''.
===== Howto =====
<related pattern="howto:*" />


===== Syntax =====

<code yaml>
columns:
  - name: columnName
    DataGenerator:
      type: expression
      ColumnParents: 
           - columnParentName1 # variable x
           - columnParentName2 # variable y
           - ...... # variable "z", "a", "b", "c", "d","e","f"
      expression: "javascriptExpression"  # See below for example
</code>



^ Mandatory Key ^  Description ^
| ''ColumnParents'' | The column generator used in the expression | 
| ''expression'' | The expression in javascript where the parents columns maps by order to the following variables "x", "y", "z", "a", "b", "c", "d","e", "f" |

===== How to hide intermediate columns ?=====

When creating an expression generator, you may want to create columns that should not appear in the data generated.
For this purpose, you can use the ''hidden'' property.

Example:
<code yaml>
- name: columnToHide
  Hidden: true  # The column will not be added to the output.
  Description: An hidden column
  DataGenerator:
    type: entity
</code>


===== Snippet of expression =====
This section is showing snippet of expression (Javascript).

==== Time ====

  * Month where ''x'' represents the ''date'' value of the first parent columns
<code javascript>
x.getMonth()+1 // Month
</code>
  * Month names. The below snippet use a ''date'' column as parent and lookup an array to get the month name.
<code javascript>
var monthNames = ['Jan', 'Feb', 'Maa', 'Apr', 'Mei', 'Jun', 'Jul', 'Aug', 'Sep', 'Okt', 'Nov', 'Dec']; 
monthNames[x.getMonth()]
</code>
  * Year number
<code javascript>
x.getFullYear()
</code>
==== Email ====
Email String concatenation where:
      * ''x'' would be a name from the first parent column
      * ''y'' would be a company name from the second parent column 
      * ''z'' would be a TLD domain extension (''.com'', ...)
<code javascript>
x+'@'+y+'.'+z
</code>

===== Data Type =====

The below data type are supported:

^ Data Type ^
| Integer |
| Float |
| Double | 
| Numeric | 
| Decimal |
| Date |
| Timestamp |
| Varchar |