Difference between revisions of "NVelocity"

Latest revision as of 21:39, 24 July 2009

NVelocity is an open source templating engine employed by AbleCommerce to accomplish certain features - most notably the email template system. By using special script and formatting codes, templates can be processed to include dynamic content. Below is an overview of some of the most basic syntax for editing email templates.

Variable Substitution

Variables are indicated by a dollar sign, and may be enclosed in curly braces. Variables can appear anywhere within the template.

Standard Syntax: $variable_name

Hello $user.PrimaryAddress.FirstName!

Explicit Syntax: ${variable_name}

Hello ${user.PrimaryAddress.FirstName}!

Standard syntax cannot be used if your variable is part of a larger string where the variable name would not be clearly defined. Below shows an example of incorrect use of the standard syntax, where explicit syntax must be used instead:

Incorrect with Standard syntax:

some_text$variable_namesome_more_text

Correct with Explicit syntax:

some_text${variable_name}some_more_text

When you reference variables you are accessing the object through the .NET framework. You can use traditional .NET syntax to access properties and methods. A common example might be to provide string formats:

$user.LastLoginDate.ToString("mm-ddd-yyyy")

nVelocity Scripting

With the nVelocity scripting language you can implement conditional logic and looping to create dynamic output. Any line that begins with a # pound sign is interpreted as a line of script.

Conditional Statements

You can employ conditional logic in your email templates with the if-end statement. For example:

#if($user.IsAnonymous)

    You can register now to get the great benefits of membership!

#else

    Welcome back $User.Username!

#end

Looping

You can loop over collections of items with the foreach-end statement. For example:

Current exchange rates for currencies:

<table>

<tr><th>Currency</th><th>Rate</th></tr>

#foreach($currency in $store.Currencies)

<tr><td>$currency.Name</td><td>$currency.ExchangeRate</td></tr>

#end

</table>

Advanced Looping

The foreach statement supports additional features to enable things like alternating rows, headers, and footers.

#foreach($i in $items)

#each

text which appears for each item

#before

text which appears before each item

#after

text which appears after each item

#between

text which appears between each two items

#odd

text which appears for every other item, including the first

#even

text which appears for every other item, starting with the second

#nodata

Content rendered if $items evaluated to null or empty

#beforeall

text which appears before the loop, only if there are items matching condition

#afterall

text which appears after the loop, only of there are items matching condition

#end

Set Statement

You can create new nVelocity variables using the set statement.

#set ($counter = 1)

Currencies provided by $Store.Name:<br />

#foreach($currency in $Store.Currencies)

$counter. $currency.Name<br />

#set ($counter = $counter + 1)

#end

<br />

All transactions are conducted in $store.PrimaryCurrency.Name.

Including Comments

You can include comments in your nVelocity script. Single line comments are created by starting a line with a ## double pound sign.

## single line comment will not be output

Multi line comments can also be included, by using the #* ... *# syntax:

#* This is a

comment that spans

multiple lines and will

not be displayed

*#

Licensing

NVelocity is distributed under the Apache License, version 1.1. AbleCommerce links to a modified version of the Castle fork of NVelocity. The modification is made from Castle's 5837 SVN revision, and is limited to adding the AllowPartiallyTrustedCallers attribute to the library. This allows the portions of the library used by AbleCommerce to work in partially trusted ASPNET environments. Our modified version of the NVelocity source code is available for download from our ftp site at ftp://ftp.ablecommerce.com/thirdparty.