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A series of property names may be specified, separated by periods: "user.name", which is equivalent to either getUser().getName() or getUser().setName(), depending on context (whether the expression is being read or updated).
The "." is called the "dereference operator". In addition, there is a a "safe dereference operator", "?.", which works the same as "." except that it allows any of the properties to be null. When reading, a null short-circuits the expression (which returns null). When writing to a property, an intermediate null value will cause the value to be discarded without error.
In other words, "user?.name" works, even when the user property may be null.
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Property expressions are compiled to Java classes at runtime; there is no runtime reflection (unlike the OGNL expression language used in prior releases of Tapestry 4 and earlier).
Grammar
Expressed in simplified Backus–Naur Form, the grammar of property expressions is as follows:
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| Example | Notes |
|---|---|---|
Keyword | this |
|
Keyword | null |
|
Property Name | userName | Calls getUserName() or setUserName, depending on context |
Property Chain | user.address.city | Calls getUser().getAddress().getCity() or getUser().getAddress().setCity(), depending on context |
Property Chain | user?.name | Calls getUser() and, if the result is not null, calls getName() on the result |
Method Invocation | groupList.size() | calls getGroupList().size() |
Method Invocation | members.findById(user.id)?.name | Calls getMembers().findById(getUser().getId())?.getName() (unless findById returns null) |
Range | 1..10 | Iterates between integers 1 and 10 |
Range | 1..groupListmyList.size() | Iterates between 1 and the result of getGroupListgetMyList().size() |
Literal String | 'Beer is proof that God loves us and wants us to be happy.' | Use single quotes |
List | [user.name, user.email, user.phone] |
|
Not Operator | ! user.deleted | the boolean negation of getUser().getDeleted() |
Not, Coerced | ! user.middleName | true only if getUser.getMiddleName() returns null or an empty string |
Map | { 'framework' : 'Tapestry', 'version' : version } | Keys are string literals (in single quotes), but could be properties as well |