I am getting following error while performing update operation:
Property 'price' is not available for write access.
updateStatement :
update istream FaultyStream set price = 100 where id = 7;
My Event class implements java.io.Serializable. Still unable to perform update.
For POJO event classes, I generate getter and setter methods. The IDE does that for me. Esper calls the setter method and that be
public void setPrice(...) {...}.
Related
I wanted to write a simple behavior in Dart to be used by a custom element.
#behavior
abstract class AlignmentBehavior implements PolymerBase {
#Property()
bool alignTop = false;
// more properties ...
ready() {
updateAlignment();
}
#reflectable
updateAlignment([_,__]) {
// reference to the element the Behavior is attached to.
// 1) Is that the correct way?
var ele = Polymer.dom(root);
// We need to inherit from PolymerBase to access set(...)
// 2) Is that the correct way?
set('alignTop', aTop);
// .. to more stuff
}
}
My first two questions are already written in the code. How do I access the element the behavior is attached to? What's the proper way of doing this? I currently use Polymer.dom(root) but I don't know if that even works since I have some runtime errors which I am going to explain later in this post. What is the official way of accessing the underlying element? Is it using the JsObject? Is it calling a Behavior function from the parent PolymerElement and pass this, or should you not access it at all?
Another question is whether I have to inherit from PolymerBase or not. The Behavior example at the Github wiki doesn't do so, but in order to access methods such as set to modify a #Property I have to inherit from it. What's the proper way of doing so?
My last two questions are about errors I get. One error asks me to implement getters and setters for my properties, such as adding a getter and setter for alignTop.
And last but not least, I cannot invoke updateAlignment() from my custom element. It says Class 'MainApp' has no instance method 'updateAlignment'.
1)
var ele = Polymer.dom(root);
If you want to access the DOM of the element, this fine.
Just root gives you the same AFAIK.
If you want to access the elements class instance, there is nothing to do. It's this but that is implicit in Dart anyway.
You can only access what is known in the mixin. To make "things" known to the mixin you can create an interface class.
abstract class MyComponentInterface {
void someFunction();
int someField;
String get someValue;
set someValue(String value);
...
}
Then implement the interface in the mixin and the element class and you have a shared contract.
abstract class AlignmentBehavior implements MyComponentInterface, PolymerBase {
The mixin can now access the members because the implementsMyComponentInterface` claims they will exist and
class MyComponent extends PolymerElement with AlignmentBehavior {
will force you to implement it to fulfill the contract of the mixin.
2) looks fine
3)
Another question is whether I have to inherit from PolymerBase or not.
Is basically the same as 1) Any Polymer element in Dart has to extend PolymerBase. To be able to access the members of PolymerBase from within the mixin it has to implement it as well. This doesn't result in any limitations because the classes that the mixin will be applied to, will fulfill that contract anyway.
If you don't need to access any members provided by PolymerBase there is no need to implement it.
So I just joined this forum because I could not find an answer to my simple question.
I want to declare a read-only property, and it should read from a private members read-only property. It seems like that won't work. Can I work myself around that blockade?
Here is the code snippet:
property Mine: TMineType read mMine.MineType;
Edit: Maybe I should clarify. mMine is of class TMine, which has a property MineType. MineType is of type TMineType and is read-only.
A property getter can be one of two things:
A field, or
A function.
Your code attempts to implement the getter with a property, and that does not meet the requirement stated above.
The documentation contains all the details: http://docwiki.embarcadero.com/RADStudio/en/Properties
On a practical level, you could do something like this:
function GetMineType : TMineType;
begin
result := mMine.MineType;
end;
property Mine: TMineType read GetMineType;
If you declare the GetMineType function as inline it will not generate any code.
Based on your additional information that you provided in your comments (such information should be put into the original question itself right from the start) I believe I can provide an answer which would hopefully provide solution to the problem you are facing.
In the code bellow I'm showing of how you can make parent class property accessible through descendant class by using property forwarding or property publishing.
//Base class we use
TBaseClass = class(TObject)
//Private section. Methods, fields and properties declared here are only visible from within classes declared in same unit
//but not from classes or method declared in other units.
private
FPrivateField: Integer;
function GetPrivateField: Integer;
procedure SetPrivateField(AValue: Integer);
//This property is making use of getter and setter methods in order to access FPrivateField
property PrivateFieldProperty: Integer read GetPrivateField write SetPrivateField;
//Strict private section. Methods, fields and properties declared here are only visible from descendant classes and their
//methods but not from other classes and their methods even if they are declared in the same unit.
strict private
FStrictPrivateField: Integer;
function GetStrictPrivateField: Integer;
procedure SetStrictPrivateField(AValue: Integer);
//Public section. Methods, Field and properties declared here are visible from any other class or methods regardless of
//where they are declared
public
//This property is accessing its field directly
property DirectPrivateFieldProperty: Integer read FPrivateField write FPrivateField;
//This property is making use of getter and setter methods in order to access FStrictPrivateField
property StrictPrivateFieldProperty: Integer read GetStrictPrivateField write SetStrictPrivateField;
end;
//Sub class is actually a descendant class from our base class
TSubClass = class(TBaseClass)
public
//If your parent class already has declared certain property and you want to use that property in your descendant
//class you can use so called "property forwarding" approach where you only specify the parents property name that
//you want to make available to your descendant class. This approach only allows accessing fields that are declared
//in parents class.
//If you need to access field declared in descendant class then its property must directly access that field or use
//getter and/or setter methods declared in descendant class. Such approach is called property overloading.
property DirectPrivateFieldProperty;
property PrivateFieldProperty;
//If you want to limit the access level of a descendants class property (making it read only) you need to follow standard
//property declaration guideline where you declare property type and the field to which it is accessing either directly or
//by using getter or setter methods
property ReadOnlyPrivateFieldProperty1: Integer read FPrivateField;
property ReadOnlyPrivatefieldProperty2: Integer read GetPrivateField;
//You can also declare forwarded descendant class property with different visibility of the one declared in parent class.
//Such approach is usually referred as property publishing.
property StrictPrivateFieldProperty;
end;
Note the above approaches only work when accessing properties or fields of a parent class from a descendant class but not for accessing fields or properties of other classes.
The reason for this is that property may only directly access fields of its own class or any parent classes.
Also property can only use getter and setter methods that are declared either in its own class or in any of the parent classes.
I hope this answer of mine might give you better idea about working with properties.
Now at the moment I guess properties might look a bit confusing to you but believe me when you will learn to work with them you will realize of how powerful they can actually be. I must admit that I'm still finding out new ways to use them in my projects every now and then.
I'm trying to annotate fields over my domain classes but I'm not able to get them at runtime by reflection as usual Java fields.
My annotated domain class looks like:
class MyDomainClass {
#MyAnnotation
String myField
}
The Java way to access myField by reflection doesn't work:
MyDomainClass.class.getField("myField") //throws java.lang.NoSuchFieldException
The Grails way to inspect domain classes doesn't expose field annotations:
new DefaultGrailsDomainClass(MyDomainClass).getPersistentProperty("myField").??? //there is nothing similar to getAnnotations()
How can I retrieve the annotations associated with a domain field?
That's not a field, it's a property. When you declare a class-scope variable like that with no scope modifier (public, protected, etc.) in a Groovy class, the Groovy compiler converts it to a private field with the same type and name, and a getter and setter method, essentially
class MyDomainClass {
#MyAnnotation
private String myField
public String getMyField() {
return myField
}
public void setMyField(String s) {
myField = s
}
}
It won't overwrite an existing getter or setter though.
When you access the property you end up calling the getter or setter, which you can see if you add those methods and include println statements. This way Java classes can access the property via those methods, and Groovy pretends that you're directly reading or writing a field but under the hood you end up calling the same methods that you would from Java.
One benefit of this is that if you decide later that you want to add some logic when setting or getting the value, you can define the corresponding method(s) and add what you want without needing to change the code that accesses the property since in Groovy you can still treat it like a field and your custom methods will be called, and Java classes will have been calling the setter and getter all along.
getFields() returns only public fields, but getDeclaredFields() returns all of them, so since the actual field is private that's why getDeclaredFields() (or the property access form declaredFields) is necessary.
Grails doesn't use annotations because Graeme (and others) feel that they're ugly and bulky, not because they're not accessible.
public function setAlbumTable(AlbumTable $albumTable)
{
$this->albumTable = $albumTable;
return $this;
}
I am talking about first parameter ( it's not parameter btw) looks like datatype ? what is it ? constant ? I encounter this when trying to develop app in zend framework 2
This is PHP's type hinting. It means that the first parameter to this function - $albumTable - must be an instance of the AlbumTable class or a class that inherits from it.
class Car {}
class BlueCar extends Car {}
function drive_the_car(Car $car) {}
drive_the_car(42); // error, first parameter must be an instance of Car
drive_the_car(new stdClass()); // error
drive_the_car(new Car()); // works
drive_the_car(new BlueCar()); // works
The piece of code you're showing is an example of dependency injection via setter method. The setter is passed an instance of AlbumTable and assignes this instance to a class field.
Your method is passed ONLY ONE parameter: $albumTable.
The AlbumTable before the parameter is a type hint and makes sure that only a instance of AlbumTable or a deriving class can be passed to the setter.
It forces the actual parameter ($albumTable) to be an instance of AlbumTable class. PHP will give a fatal error if anything else is passed to the function.
This is useful so you don't have to check what type of variable/object you received in order to make use of it's functions and properties.
[Bindable]
/**
* Display output of video device.
*/
public var videoLocal : Video;
Anyone knows?
[Bindable] is a one of several meta tags that you can use in flex ActionScript code. It can be applied to properties, or methods that are marked in any scope. It cannot be used with static class members.
The key to using the [Bindable] meta tag is understanding what is going on under the hood when you use it. Essentially using data binding is a type of shorthand for adding event listeners and dispatching events.
There are two basic forms of the [Bindable] tag. The first is just [Bindable] followed by a var/property declaration. The Second is [Bindable(event="eventname")] followed by either a var/property declaration, a function/method declaration or one half of a getter/setter declaration.
I'll explain the longer notation first since the other builds on the same concept but with even more shorthand.
When you use [Bindable(event="eventname")] you are essentially telling the compiler that this var/property/function/method (call this the instance member) is 'available' to be used as the source for data binding. You are also telling it that when the value of the instance member has been invalidated/changed and it needs to be re-read that the "eventname" event will be dispatched.
In this longer form this all you are doing. You the developer are responsible for actually dispatching the "eventname" event whenever the value needs to be updated in the binding subscribers.
The real efficiency of using data binding comes on the subscribing side. The typical notation you will see in MXML is value="{instance.propertyName}" When you use the notation { } you are telling the compiler to do the following:
Create an event listener that listens to the event named in the bindable meta tag
In that event listener re-read the instance.propertyName and update this value
If you use the shorter form [Bindable], and you add the tag before a property/var, the compiler fills in the blanks and adds some additional functionality to make the property bindable. Essentially you are telling the compiler "add the events and methods you need to make this property bindable"
Now the way to think of what the compiler will do under the hood is this.
make a private version of your var
create an "event" to trigger the binding
create a getter function with scope and name of your original var that returns the private verson of the var when called.
create a setter function with scope and name of your original var that sets the private version of the var when called AND dispatches the triggering event.
In essence the compiler will do much of the work for you.
[Bindable]
public var xyz
is equivalent to
private var _xyz:String;
[Bindable(event="updateXYZValue")]
public function get xyz():String{
return _xyz;
}
public function set xyz(newxyz:String):void{
_xyz = newxyz;
dispatchEvent(new Event("updateXYZValue"));
}
The only functional differences in these is that in the first instance;
you do not know the name of the event that will be dispatched to trigger the binding
there is no way to update the underlying value without triggering the data binding
This second example also demonstrates one special case of the [Bindable] meta tag. This is that when you are applying it to a getter/setter pair defined for the same variable name you need only apply it to one or the other, it will apply to both. Typically you should set it on the getter.
You can use either notation on a function/method however if you do not specify an event the binding will never be triggered so if you are trying to bind to a function you should alway specify an event. It is also possible to specify more than one triggering event by stacking the tag. eg.
[Bindable(event="metaDataChanged")]
[Bindable(event="metaObjectUpdated")]
public function readMyMetaData():MetaDataObject{
var myMetaDataObject:MetaDataObject;
.
.
.
return myMetaDataObject;
}
This would presume that somewhere else you your class you will dispatch this metaDataChanged event or the metaObjectUpdated event when you want trigger the binding.
Also note that with this notation you can tie the binding of any instance member to any event that the instance will dispatch. Even inherited events that you yourself do not generate such as FrameEnter, OnChange, etc...
Data bindings can also be setup and destroyed during runtime. If you are interested in this take a look at the mx.binding.utils classes.
It is used in Databinding with Flex, you can read more about it here
http://livedocs.adobe.com/flex/3/html/help.html?content=databinding_2.html
Creating properties to use as the source for data binding
When you create a property that you
want to use as the source of a data
binding expression, Flex can
automatically copy the value of the
source property to any destination
property when the source property
changes. To signal to Flex to perform
the copy, you must use the [Bindable]
data tag to register the property with
Flex.
As an addition to what Justin said, you can actually use two ways data binding in Flex with the # character. Here's an example:
<s:TextInput id="txt1" text="#{txt2.text}" />
For a working example with source code enabled you can check out this article I wrote a while back:
Two-ways data binding in Flex