Using boolean conditions

Boolean conditions are queries that compare two values with each other (e.g. with == or >=) and then returns the value true or false. Which values are interpreted as true or false by Fluid depends on the data type. A number for example is evaluated as true if it is greater than 0.

Tip

You find a complete list of all evaluating possibilities in appendix C in the section “Boolean expressions”.

With the help of conditions you can hide or show certain parts of a template. A typical scenario is the display of search results: If search results are found, they were displayed; if none results are found an appropriate message should be displayed. In Fluid the IfViewHelper enables such case-by-case analysis.

Simple if queries (without an else term) looks like this:

<f:if condition="{blog.posts}">
This is only shown if blog posts are available.
</f:if>

Tip

If none comparison operator like == is given, per default empty lists are interpreted as false and list with at least one element as true.

Using the inline notation it looks like this:

<div class="{f:if(condition: blog.posts, then: 'blogPostsAvailable')}">
This div has the CSS class 'BlogPostAvailable', if blog posts are available.
</div>

Also if-then-else structures are possible. In that case the then tag is required:

<f:if condition="{blog.posts}">
<f:then>
This is only shown if blog posts are available.
</f:then>
<f:else>
No blog posts available.
</f:else>
</f:if>

This is also possible in the inline notation:

<div class="{f:if(condition: blog.posts, then: 'blogPostsAvailable', else: 'noPosts')}">
This div has the CSS class 'BlogPostAvailable', if blog posts are available.
If no posts are available this div container gets the CSS class 'noPosts' assigned.
</div>

Realize complex comparisons

Until now we have employed with simplest boolean evaluations. With the syntax you have learned until now, no comparisons or modulo operations are possible. Fluid supports these conditions as well. Here is a short example:

<f:if condition="{posts.viewCount} % 2">
viewCount is an even number.
</f:if>

Note the enhanced syntax inside the condition. The compare operators >, >=, <, <=, ==, != and % are available. The parameter left and right of the operators could be numbers, object accessors, arrays and ViewHelpers in inline notation, but not strings.

Tip

Comparisons with strings, like <f:if condition="{gender} == 'male'">....</f:if>, are not possible with Fluid yet because of the complex implementation. If you need such a condition, you have to write a ViewHelper that returns the needed string. Then you can compare the object accessor with the output of the ViewHelper:

<f:if condition="{gender} == {my:male()}">...</f:if>

The just shown detailed notation for comparisons and modulo operations is not only available for the if ViewHelper but for all ViewHelpers which have a parameter of the type boolean.

Tip

Once you develop an own ViewHelper - like described in the section “<xref linkend=”Fluid_custom_viewHelper” />” later on in this chapter - you can use boolean expressions as arguments. Therefore the ViewHelper has to mark all arguments where those expressions are to be used as boolean. The just explained functionality is not only available in the if ViewHelper, but rather available in self developed ViewHelper.<remark> ??? Sentence is not very clear</remark>

Upon engaged with many functionalities for the author of templates in this section, we would show you now how to develop your own ViewHelper.<remark>??? Does anyone understand the first part of the sentence?</remark>