Gentics CMS-OSS Documentation

Chapters

1. Configuration and usage

2. ExpressionParser Syntax

   • Binary Operations

   • Unary Operators

   • Constants

   • Literals

   • Names and Variables

   • Functions

   • Evaluation priority

3. Examples

   • Conditionally choose a value to be written in the tagmap

   • Concatenate two or more values before writing them in to the tagmap

1 Configuration and usage

To enable the ExpressionParser for the column “tagname” of the Tagmap set the feature ‘tagmap_useexpressionparser’ to true.

feature:
	tagmap_useexpressionparser: true

When the feature is enabled it is possible to use Expressions in the column “tagname” instead of simple references to object properties or tag values. These Expressions are evaluated each time the object is published and the result of this evaluation is written to the ContentRepository.

2 ExpressionParser Syntax

This section describes the valid syntax for expressions. In general an Expression is any legal combination of Operations, Constants, Literals, Names and Functions.

2.1 Binary Operations

Binary Operations define how operators (left hand side [lhs] operator and righ hand side [rhs] operator) shall be combined to calculate other values. The supported values of the operators and the generated value depend on the Operator and are listed below.

2.2 Unary Operators

Unary Operations modify values of a single operand.

2.3 Constants

There are three constants: true, false and null (empty value).

2.4 Literals

There exist four types of literals: integer numbers, floating point numbers, strings and arrays.

Examples of literals in expressions

42 (decimal integer)
-99 (signed decimal integer)
0xff (hexadecimal integer, decimal value: 255)
010 (octal integer, decimal value: 8)
-18.98e+1 (floating point integer, value: -189.8)
31.415926e-1 (floating point integer, value: 3.1415926)
"Franz" (string literal)
'Sepp' (string literal)
"\"'\n\t" (string literal, containing escaped characters)
["Franz", 42, true] (array)
[['Sepp', 1.95], ['Franz', 1.84]] (nested arrays)

2.5 Names and Variables

All character sequences that are not operators, literals, constants or functions (see below) and for which the rules for Java identifiers apply, are interpreted as names. Sequences of names that are only separated by . (dots) are interpreted as name-paths. When expression containing names are evaluated, name-paths are resolved into their current values (which might be null). Special name-paths starting with object. are interpreted as variables. When the expression is used as filter for datasource queries, the variables are placeholders for attributes of the filtered objects and their properties. For details on Java identifiers, see the Javadoc for Character.isJavaIdentifierPart() .

2.6 Functions

Functions are Names followed by parenthesis () . Functions might have function parameters that can be Literals, Constants, Name-paths, Functions or even Expressions.

2.7 Evaluation priority

The evaluation priority of different expression parts can be seen in the following table (operations with highest priority listed on top):

1. Constants, Literals, Names and Functions
2. Unary operations
3. Multiplicative calculation operations
4. Additive calculation operations
5. Comparison operations
6. Boolean operations
7. Assignments

Sequences of operations with the same priority level are evaluated from right to left. It is legal to use parenthesis within expressions to modify the evaluation order.

3 Examples

3.1 Conditionally choose a value to be written in the tagmap

If the tag-part “email” of the “author” tag in the page is filled (!isempty()) the contents of the tag-part will be written into the tagmap, otherwise the email of the page creator (CMS-User).

if(!isempty(page.tags.author.email.text), page.tags.author.email, page.creator.email)

3.2 Concatenate two or more values before writing them in to the tagmap

concat(object.author.firstname, " ", object.author.lastname, " (", object.author.email, ")")

This would produce, given the object property with the given parts exists, an output like “Jane Doe (jane.doe@example.com)” for the attribute value in the ContentRepository.