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


===== About =====
A ''expression data-supplier'' is a [[data-supplier|column data supplier]] that can generate data created from:
  * other columns (known as ''parent columns'')
  * by giving an ''expression (or formula)''.


===== Example =====

  * [[:howto:generator:expression]]
===== Syntax =====

<code yaml>
columns:
  - name: column_name
    data-supplier:
      type: expression
      arguments:
          # The name of a column used in the expression
          column-variable: columnVariableName # becomes in the expression, the variable columnvariablename 
          # A list of column name used in the expression
          column-variables:
              - columnVariableName1 # becomes in the expression, the variable columnvariablename1 
              - columnVariableName2 # becomes in the expression, the variable columnvariablename2
              - ...... 
          # The expression
          expression: "javascriptExpression"  
</code>

==== Arguments ====


The [[:docs:conf:parameter|arguments]] of the [[:docs:generator:data-supplier|data supplier node]] are:

^ Name ^ Description ^
| ''column-variable'' | A column name used in the expression as variable |
| ''column-variables'' | A list of column names used in the expression as variables |
| ''expression'' | The [[#expression]] |

===== What are Expressions ?=====

Expressions are Javascript expressions.


Tabulify pass the data as native javascript [[docs:data_type:data_type|data type]] in a variable with the name of the column in lowercase.
You don't need to instantiate the variables, Tabulify do.



Note:
  * For [[docs:data_type:date_time|date/timestamp/time data type]], we create a [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date|Date]] as this is the only temporal data type of javascript.
  * For all numbers (Double, Integer, ...) , we create a [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number|Number]] as this is also the only number data type of javascript.

Example for ''2009/10/01'' and the column name ''date'' or ''DATE'', Tabulify would create the `date` variable like this:
<code javascript>
date = new Date("2009","10","01")
</code>
And if you want the month, you expression would use [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getMonth|getMonth]] :
<code javascript>
date.getMonth()+1
</code>



===== 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
  data-supplier:
    type: entity
</code>






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

The below [[docs:data_type:data_type|data type]] are supported:

^ Data Type ^ Java script Equivalent ^
| [[:docs:data_type:integer|Integer]] | [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number|Number]] |
| [[:docs:data_type:double_real_float|Double/Float]] | [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number|Number]] |
| [[:docs:data_type:numeric_decimal|Numeric/Decimal]] | [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number|Number]] |
| [[:docs:data_type:date_time|Date/Timestamp]] | [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date|Date]] |
| [[..:data_type:character|Varchar/Char]] | [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String|String]] |