Rules engine APIs for evaluating conditions and generating filters

Rules engine APIs for evaluating conditions and generating filters

Evaluating conditions

The rulesEngineConditionService.evaluateCondition() method allows you to evaluate a saved condition at runtime.

For example, let's imagine that we have a slideshow_slide object that allows you to configure picture, link, title, etc. for a slide in a slide show. It would be great if we could configure it to show only when the chosen condition is true (e.g. only show the promo for our Conference if you have not already booked on it). Our Preside Object might look like this:

// slideshow_slide.cfc
component {
    // ...

    // ruleContext below tells the auto generated condition picker
    // formcontrol to limit conditions to "webrequest" compatible conditions
    property name="condition" relationship="many-to-one" relatedTo="rules_engine_condition" ruleContext="webrequest";
    // ...

The logic to then decide whether or not to show the slide:

// /handlers/somehandler.cfc
component {
    property name="slidesService"               inject="slidesService";
    property name="rulesEngineConditionService" inject="rulesEngineConditionService"; 

    private string function slides() {
        var slides         = slidesService.getMySlides( ... );
        var renderedSlides = "";

        for( var slide in slides ) {
            // show the slide if it has no condition, or the condition evaluates
            // to true. notice the "webrequest" context that matches the conditions
            // that we are allowed to choose (see object definition, above)
            var showSlide = !Len( Trim( slide.condition ) ) || rulesEngineConditionService.evaluateCondition( 
                  conditionId = slide.condition
                , context     = "webrequest" 
            if ( showSlide ) {
                renderedSlides &= renderView( view="/slides/_slide", args=slide );

        return renderedSlides;


The default form control for properties that relate to rules_engine_condition and that define a ruleContext is Form control: Condition picker. You can also use this control and its options directly in your form definitions if you so need.

Using saved filters

You can use saved filters in your everyday code to enhance the user experience and flexibility of your systems. Given a saved filter ID (from the rules_engine_condition object), you can use the RulesEngineFilterService.prepareFilter() method to get an extraFilters filter array to pass to your selectData() call.

A useful example of this is a "Latest news" widget that allows you to choose a dynamic filter with which to filter the news to show. The widget form could look like this (see Form control: Filter picker for documentation on the filter picker):

<?xml version="1.0" encoding="UTF-8"?>
<form i18nBaseUri="widgets.latestnews:">
    <tab id="default" sortorder="10">
        <fieldset id="default" sortorder="10">
            <field name="title"  control="textinput" />
            <field name="filter" control="filterpicker" filterobject="news" />

The service logic to use the saved filter might then look like this:

// /services/NewsService.cfc
component {
    // ...

    public query function getLatestNews( string filter="" ) {
        var extraFilters = [];

        if ( arguments.filter.len() ) {
            extraFilters.append( rulesEngineFilterService.prepareFilter(
                  objectName = "news"
                , filterId   = arguments.filter
            ) );

        return newsDao.selectData(
              filter       = { published = true }
            , extraFilters = extraFilters
            , orderby      = "publish_date desc"

    // ...


If you are persisting a filter choice to the database (as opposed to just using in a widget), create a property with a relationship to the rules_engine_condition object. e.g.

// /preside-objects/my_object.cfc
component {
    // ...

    property name="required_filter"  relationship="many-to-one"  relatedto="rules_engine_condition" control="filterpicker" filterobject="my_object";
    property name="optional_filters" relationship="many-to-many" relatedto="rules_engine_condition" relatedvia="my_object_optional_filter" control="filterpicker" filterobject="my_object" multiple=true;

    // ...