Eel, FlowQuery and Fizzle

Eel - Embedded Expression Language

Besides simple Fusion assignments such as myObject.foo = 'bar', it is possible to write expressions using the Eel language such as myObject.foo = ${q(node).property('bar')}.

The Embedded Expression Language (Eel) is a building block for creating Domain Specific Languages. It provides a rich syntax for arbitrary expressions, such that the author of the DSL can focus on its Semantics.

In this section, the focus lies on the use of Eel inside Fusion.

Syntax

Every Eel expression in Fusion is surrounded by ${...}, which is the delimiter for Eel expressions. Basically, the Eel syntax and semantics is like a condensed version of JavaScript:

Most things you can write as a single JavaScript expression (that is, without a ;) can also be written as Eel expression.
Eel does not throw an error if null values are dereferenced, i.e. inside ${foo.bar} with foo being null. Instead, null is returned. This also works for calling undefined functions.
Eel does not support control structures or variable declarations.
Eel supports the common JavaScript arithmetic and comparison operators, such as +-*/% for arithmetic and == != > >= < <= for comparison operators. Operator precedence is as expected, with multiplication binding higher than addition. This can be adjusted by using brackets. Boolean operators && and || are supported.
Eel supports the ternary operator to allow for conditions <condition> ? <ifTrue> : <ifFalse>.
When object access is done (such as foo.bar.baz) on PHP objects, getters are called automatically.
Object access with the offset notation is supported as well: foo['bar']

This means the following expressions are all valid Eel expressions:

${foo.bar}         // Traversal
${foo.bar()}       // Method call
${foo.bar().baz()} // Chained method call

${foo.bar("arg1", true, 42)} // Method call with arguments

${12 + 18.5}         // Calculations are possible
${foo == bar}      // ... and comparisons

${foo.bar(12+18.5, foo == bar)} // and of course also use it inside arguments

${[foo, bar]}           // Array Literal
${{foo: bar, baz: test}} // Object Literal

Semantics inside Fusion

Eel does not define any functions or variables by itself. Instead, it exposes the Eel context array, meaning that functions and objects which should be accessible can be defined there.

Because of that, Eel is perfectly usable as a “domain-specific language construction kit”, which provides the syntax, but not the semantics of a given language.

For Eel inside Fusion, the semantics are as follows:

All variables of the Fusion context are made available inside the Eel context.
The special variable this always points to the current Fusion object implementation.
The function q() is available, which wraps its argument into a FlowQuery object. FlowQuery is explained below.

By default the following Eel helpers are available in the default context for Eel expressions:

String, exposing Neos\Eel\Helper\StringHelper
Array, exposing Neos\Eel\Helper\ArrayHelper
Date, exposing Neos\Eel\Helper\DateHelper
Configuration, exposing Neos\Eel\Helper\ConfigurationHelper
Math, exposing Neos\Eel\Helper\MathHelper
Json, exposing Neos\Eel\Helper\JsonHelper
Security, exposing Neos\Eel\Helper\SecurityHelper
Translation, exposing Neos\Flow\I18n\EelHelper\TranslationHelper
Neos.Node, exposing Neos\Neos\Fusion\Helper\NodeHelper
Neos.Link, exposing Neos\Neos\Fusion\Helper\LinkHelper
Neos.Array, exposing Neos\Neos\Fusion\Helper\ArrayHelper
Neos.Rendering, exposing Neos\Neos\Fusion\Helper\RenderingHelper

See: Eel Helpers Reference

This is configured via the setting Neos.Fusion.defaultContext.

Additionally, the defaultContext contains the request object, where you have also access to Arguments. e.g. ${request.httpRequest.arguments.nameOfYourGetArgument}

FlowQuery

FlowQuery, as the name might suggest, is like jQuery for Flow. It’s syntax has been heavily influenced by jQuery.

FlowQuery is a way to process the content (being a Neos ContentRepository node within Neos) of the Eel context. FlowQuery operations are implemented in PHP classes. For any FlowQuery operation to be available, the package containing the operation must be installed. Any package can add their own FlowQuery operations. A set of basic operations is always available as part of the Neos.Eel package itself.

In Neos.Neos, the following FlowQuery operations are defined:

property: Adjusted to access properties of a Neos ContentRepository node. If property names are prefixed with an underscore, internal node properties like start time, end time, and hidden are accessed.
filter: Used to check a value against a given constraint. The filters expressions are given in Fizzle, a language inspired by CSS selectors. The Neos-specific filter changes instanceof to work on node types instead of PHP classes.
children: Returns the children of a Neos ContentRepository node. They are optionally filtered with a filter operation to limit the returned result set.
parents: Returns the parents of a Neos ContentRepository node. They are optionally filtered with a filter operation to limit the returned result set.

A reference of all FlowQuery operations defined in Neos.Eel and Neos.Neos can be found in the FlowQuery Operation Reference.

Operation Resolving

When multiple packages define an operation with the same short name, they are resolved using the priority each implementation defines, higher priorities have higher precedence when operations are resolved.

The OperationResolver loops over the implementations sorted by order and asks them if they can evaluate the current context. The first operation that answers this check positively is used.

FlowQuery by Example

Any context variable can be accessed directly:

${myContextVariable}

and the current node is available as well:

${node}

There are various ways to access its properties. Direct access is possible, but should be avoided. It is better to use FlowQuery instead:

${q(node).getProperty('foo')} // Possible, but discouraged
${q(node).property('foo')} // Better: use FlowQuery instead

Through this a node property can be fetched and assigned to a variable:

text = ${q(node).property('text')}

Fetching all parent nodes of the current node:

${q(node).parents()}

Here are two equivalent ways to fetch the first node below the left child node:

${q(node).children('left').first()}
${q(node).children().filter('left').first()}

Fetch all parent nodes and add the current node to the selected set:

${node.parents().add(node)}

The next example combines multiple operations. First it fetches all children of the current node that have the name comments. Then it fetches all children of those nodes that have a property spam with a value of false. The result of that is then passed to the count() method and the count of found nodes is assigned to the variable ‘numberOfComments’:

numberOfComments = ${q(node).children('comments').children("[spam = false]").count()}

The following expands a little more on that. It assigns a set of nodes to the collection property of the comments object. This set of nodes is either fetched from different places, depending on whether the current node is a ContentCollection node or not. If it is, the children of the current node are used directly. If not, the result of this.getNodePath() is used to fetch a node below the current node and those children are used. In both cases the nodes are again filtered by a check for their property spam being false.

comments.collection = ${q(node).is('[instanceof Neos.Neos:ContentCollection]') ?
        q(node).children("[spam = false]") : q(node).children(this.getNodePath()).children("[spam = false]")}

Querying for nodes of two or more different node types

elements = ${q(node).filter('[instanceof Neos.NodeTypes:Text],[instanceof Neos.NodeTypes:TextWithImage]').get()}

Fizzle

Filter operations as already shown are written in Fizzle. It has been inspired by the selector syntax known from CSS.

Property Name Filters

The first component of a filter query can be a Property Name filter. It is given as a simple string. Checks against property paths are not currently possible:

foo          //works
foo.bar      //does not work
foo.bar.baz  //does not work

In the context of Neos the property name is rarely used, as FlowQuery operates on Neos ContentRepository nodes and the children operation has a clear scope. If generic PHP objects are used, the property name filter is essential to define which property actually contains the children.

Using Multiple Filters

It is possible to combine multiple filters:

[foo][bar][baz]: All filters have to match (AND)
[foo],[bar],[baz]: Only one filter has to match (OR)