Overview
OGNL is the Object Graph Navigation Language - see http://www.ognl.org for the full documentation of OGNL. In this document we will only show a few examples of OGNL features that co-exist with Webwork.
Basic Expressions
To review basic concepts, refer to OGNL
Collections (Maps, Lists)
Dealing with collections(map,list) in webwork comes often, so here are a few examples using the select tag:
Syntax for list: {e1,e2}. This creates a List containing the String "name1" and "name2."
<webwork:select label="'lebal'" name="'nmae'" list="{'name1','name2'}" />
Syntax for map: #{key1:value1,key2:value2}. This creates a map that maps the string "foo" to the string "foovalue" and "bar" to the string "barvalue":
<webwork:select label="'lebal'" name="'nmae'" list="#{'foo':'foovalue', 'bar':'barvalue'}" />
You may need to determine if an element exists in a collection. You can accomplish this with the operations in
and not in
<ui:if test="'foo' in {'foo','bar'}"> muhahaha </ui:if> <ui:else> boo </ui:else> <ui:if test="'foo' not in {'foo','bar'}"> muhahaha </ui:if> <ui:else> boo </ui:else>
To select a subset of a collection (called projection), you can use a wildcard within the collection.
- ? - All elements matching the selection logic
- ^ - Only the first element matching the selection logic
- $ - Only the last element matching the selection logic
To obtain a subset of just male relatives from the object person:
person.relatives.{?this.gender == 'male'}
Lambda Expressions
For all you math majors who didn't think you would ever see this one again.
fibonacci: if n==0 return 0; elseif n==1 return 1; else return fib(n-2)+fib(n-1);
fib(0) = 0
fib(11) = 89
The lambda expression is everything inside the brackets. The #this variable holds the argument to the expression, which is initially starts at 11.
<ui:property value="#fib =:[#this==0 ? 0 : #this==1 ? 1 : #fib(#this-2)+#fib(#this-1)], #fib(11)" />
Note: You are expected to have that memorized after one minute