How to properly check that some %ZEN.proxyObject's object has a specific property?
In my case I have %ZEN.proxyObject instance. My guess is set p = $PROPERTY(object, "propertyName"). $PROPERTY returns an empty string if property does not exists, but what if the property value is an empty string?
Use %data property of %ZEN.proxyObject:
Set obj = ##class(%ZEN.proxyObject).%New()
Set obj.a = 2
Write $Data(obj.%data("a"))
>1
Write $Data(obj.%data("b"))
>0
Related
My Objective is:
Using MATLAB, set the property value within one class method, and the property values are different between instances.
My Problem is:
When using SET in the class method, I will change the property value of all instances of this class, which is not what I want. I only want to change the property value of this instance.
About the dynamic property: I think it's used to create a unique property of the instance instead of setting the unique value of a general class property, is that right?
Code example:
classdef Storage
properties
tree = containers.Map('KeyType','int32', 'ValueType','any')
end
methods
function obj = set_tree(obj,period, value)
obj.tree(period) = value;
end
end
end
When setting the value using this method:
st1 = Storage();
st2 = Storage();
st1 = st1.set_tree(10,1);
st2 = st2.set_tree(10,2);
Right now, the value set to st2.tree(10) will override the value set to st1.tree(10), which I am trying to avoid.
The problem you're having is caused by setting a handle class object as a default value for a class property. The relevant documentation says this:
MATLAB® evaluates property default values only once when loading the class. MATLAB does not reevaluate the assignment each time you create an object of that class. If you assign an object as a default property value in the class definition, MATLAB calls the constructor for that object only once when loading the class.
So, for your Storage class above, all of your instances will be using the same default containers.Map object stored in the tree property. And since the containers.Map class is a subclass of the handle class it has reference behavior, which means the copies of the object will all point to the same underlying key/value map. If you want independent objects for each instance, you can initialize the tree property in the constructor:
classdef Storage
properties
tree
end
methods
function obj = Storage()
obj.tree = containers.Map('KeyType','int32', 'ValueType','any');
end
function obj = set_tree(obj, value, period)
obj.tree(period) = value;
end
end
end
I am having scenario in which i want to fetch all the values of a property under a specific path in AEM using QueryBuilder api.
This property can have single or multivalued.
Any help will be appreciated!!
Example that can help you. is below as it is just for illustration written in simple JSP scriptlets
<%
Iterator<Resource> iter = resourceResolver.findResources("/jcr:root/content/geometrixx-outdoors//element(*, nt:unstructured)[(#imageRotate = '0' or #imageRotate = '1')]","xpath");
while (iter.hasNext()) {
Resource child = iter.next();
out.println("</br>"+child.getPath());
Node node = child.adaptTo(Node.class);
Property nProp = node.getProperty("imageRotate");
if(nProp.isMultiple()) // This condition checks for properties whose type is String[](String array)
{
Value[] values = nProp.getValues();
out.println(" :: This is a multi valued property ::");
for (Value v : values) {
out.println("</br>"+"Property Name = "+nProp.getName()+" ; Property Value= "+v.getString());
}
}
else if(!nProp.getDefinition().isMultiple()){
out.println("</br>"+"Property Name = "+nProp.getName()+" ; Property Value= "+nProp.getString());
}
}
%>
Here i have used the Iterator<Resource> iter = resourceResolver.findResources(query,"xpath"); which can give you the query results which matches the imageRotate property under /content/geometrixx-outdoors/ path which consists combination of single and multivalued as shown in below screenshot.
There is no direct way to fetch the properties using query builder api. I would suggest you to create a servlet resource, which requires a path and property name.
Fetch the jcr node using the given path via QueryBuilder. Then, you need to loop through the results to check the property of the nodes. You can access the multiple property values, once you have a node.
So I have Class
class MyClass
....do things...
and I add objects to it with
ObjName = MyClass(things)
and my problem is that when I add ObjName to MyClass in a loop, I can't figure out a way to create a new object name each loop so it keeps overwriting the only Obj this ends up creating. I tried adding a list as in
ObjName[i] = MyClass(things)
but it wouldn't work.
Here is what I'm trying to do specifically (edited for clarity):
So when I add objects to MyClass, the name of the object added should be callable with input, like so:
somename = input("objname: ") # User input decides how the object values can be called
TempObjName = MyClass(things) # Values of the specific object, will contain more than one unique object
*...*
somename.someattribute() ## 2 different
somename2.someattribute() ## values, sets or etc
Try this:
ObjList = []
for i in whatever:
temp = MyClass(things)
ObjList.extend(temp)
I wasn't able to create the function I wanted per-say, but because my code had a dictionary that saved the obj name and obj value in it, I was able to do what I initially wanted to do by rerunning the requested name from the dictionary in the Class.
Let's started with the code snippet:
St Foo {
var proA: Int = 0 { // needs initialization
willSet {
print("about to set proA to \(newValue) from \(proA)")
}
didSet {
print("already set proA to \(proA) from \(oldValue)")
}
}
var ProB: Int { // do not needs initialization
return 1
}
}
let foo = Foo()
foo.proA = 23
print(foo.ProB)
Here are some of my personal understandings about the the stored and computed property:
a: Property with only the observer (willSet and didSet) is not a computed property but a stored property (ex. the proA property in the code above).
b: Computed property must not has initialization (See the comments of the code above).
c: setter is kind of equal to the property observer, the property observer is just the setter + the observer to of the before and after mutating.
Questions:
1. I wonder what makes a property a computed property? Is it correct that as long as the property has a getter and return it is a computed property?
2. Are all my understandings (a, b & c) correct? If not, would be nice of you to point out.
3. Why is it not allowed to initialize an computed property? (Please see the figure below) And when I do so the compiler gives out the warning Cannot call value of none-function type "int" What's the meaning of this error?
Thanks a lot.
First, this is about variables, not properties. Any variable can be a computed variable. A property is just one way to use a variable.
I think on the whole you are making a big mistake in putting a stored variable with setter observers side by side with a computed variable. They are unrelated!
Think of a computed variable as something that looks and acts like a variable when you use it — you get and (maybe) set it — but is in fact a function (or a pair of functions). It is just a compact way of calling a function. That's all it is.
A stored variable with observers, on the other hand, is just a stored variable that also has some observers.
Okay, on to your questions:
I wonder what makes a property a computed property? Is is correct that as long as the property has a getter and return it is a computed property?
Yes. It's a computed variable because you declared it using the syntax that makes it a computed variable (with the curly braces).
Are all my understandings (a, b & c) correct? If not would be nice of you to point out
Yes. I think your "c" is quite insightful: a computed variable does not need a setter observer because it has (gasp!) a setter!
Why is it not allowed to initialize an computed property? (Please see the figure below) And when I do so the compiler gives out the warning Cannot call value of none-function type "int" What's the meaning of this error?
There is no sense in which a computed variable "has" a value — it is computed! it's just some functions! — so it makes no sense to assign it an "initial" value.
A stored property is a property of which the property value is stored together with the instance of the class or struct. The value may be changed, but the property can also be a constant. Thus a stored property can be as simple as:
var proA: Int
let proB: Int
var proC: Int = 0
Computed properties do not store a value. Thus you cannot assign a value to a computed property. A Computed property should have a getter that returns a value. I a broad term, you can think of a computed property as a property that returns the value of a function.
Example of Computed Property
var proA: Int {
return proB * proC
}
With regards to your questions:
Computed Property is therefor a property that do not store a value, and contains a get to return the 'computed' value of the property.
a is correct, b computed properties should not have initialization, c if you mean willSet and didSet. Yes they are like observers for when the property's value will change and did change respectively
Since the value of a computed property is not stored and will never be used, the compiler forbids it.
Hope this helps a bit.
I wonder what makes a property a computed property? Is is correct that as long as the property has a getter and return it is a computed property?
If you define get { } inside the property declaration, it makes that property to a computed property.
And it cannot have initial value as when you access the property, it will always call get{} function declared in property.
Are all my understandings (a, b & c) correct? If not would be nice of you to point out
a is correct
b is wrong.
You can not set initial value for computed property.
Because as I explained in question 1, it will always return result of get{} when you need access to the property.
c : 50% right
setter , it can also be used as to store newValue into another private variable and you can do some additional observing logic. So to observe value changes on stored property, you use willSet and didSet
You can define observing logic on computed property (which has getter and setter) on set{} declaration. But main purpose of set {} is to store the value to another variable or for example UserDefaults.
Why is it not allowed to initialize an computed property? (Please see the figure below) And when I do so the compiler gives out the warning Cannot call value of none-function type "int" What's the meaning of this error?
Same answer
Your code makes compiler to be confused
When you set initial value on the property on declaration, the compiler tries to understand it as stored property. But you also defined get{} for this property, and it means it is computed property and should always return 22 when you access the property. So you should remove one of two.
a. Yes,a property with only observer is a stored property not a computed property.Beacuase property observer tracks the value of a property whose value has initialised previously & it's now changing ,that's a stored property. It's not applicable for a computed property since it has no predefined value
b. computed property is a property whose value depends on other variables, we should declare only those properties as computed property , who needs to be computed using value of another variables ,so it's value cannot be initialised in advance.
for e.g. - If we have 2 variables a & b. we need their addition value , so a variable named 'sum' is used , then sum will be declared as a computed property & its get{} block will return (a+b) that's sum of a & b & the value of sum variable.Then in this case we can't initialise property 'sum'
in advance because it will be computed using a & b.
c. Setter is not an observer it sets value of another variable or performs some actions related to other variables whereas a property observer tracks changes in value of its associated variable itself. for e.g. it's meaningless to use a property observer for variable 'sum' as described in point b .
I have a custom class module in VBA (Access) that is supposed to handle a large amount of external data. Currently I have two functions Read(name) and Write(name, value) that allows to read and set dynamic properties.
Is there a way to define a more syntactic way to read and write those data? I know that some objects in VBA have a special way of accessing data, for example the RecordSet, which allows to read and set data using myRS!property_name. Is there a way to do exactly the same for custom class modules?
The exclamation mark syntax is used to access members of a Scripting.Dictionary instance(you'll need to add a reference to Microsoft Scripting Runtime through Tools > References first). To use this syntaxyou'll need to be storing the information internally in a dictionary.
The quickest way to use it in a class is to give your class an object variable of type Scripting.Dictionary and set it up as follows:
Option Explicit
Dim d As Scripting.Dictionary
Private Sub Class_Initialize()
Set d = New Scripting.Dictionary
End Sub
Private Sub Class_Terminate()
Set d = Nothing
End Sub
Public Property Get IntData() As Scripting.Dictionary
Set IntData = d
End Property
Now you can access properties using myinstance.IntData!MyProperty = 1... but to get to where you want to be you need to use Charlie Pearson's technique for making IntData the default member for your class.
Once that's done, you can use the following syntax:
Dim m As MyClass
Set m = New MyClass
Debug.Print "Age = " & m!Age ' prints: Age =
m!Age = 27
Debug.Print "Age = " & m!Age ' prints: Age = 27
Set m = Nothing
Okay, thanks to Alain and KyleNZ I have now found a working way to do this, without having a collection or enumerable object below.
Basically, thanks to the name of the ! operator, I found out, that access via the bang/pling operator is equivalent to accessing the default member of an object. If the property Value is the default member of my class module, then there are three equivalent statements to access that property:
obj.Value("param")
obj("param")
obj!param
So to make a short syntax working for a custom class module, all one has to do is to define a default member. For example, I now used the following Value property:
Property Get Value(name As String) As String
Value = SomeLookupInMyXMLDocument(name)
End Property
Property Let Value(name As String, val As String) As String
SetSomeNodeValueInMyXMLDocument(name, val)
End Property
Normally, you could now access that like this:
obj.Value("foo") = "New value"
MsgBox obj.Value("foo")
Now to make that property the default member, you have to add a line to the Property definition:
Attribute Value.VB_UserMemId = 0
So, I end up with this:
Property Get Value(name As String) As String
Attribute Value.VB_UserMemId = 0
Value = SomeLookupInMyXMLDocument(name)
End Property
Property Let Value(name As String, val As String) As String
Attribute Value.VB_UserMemId = 0
SetSomeNodeValueInMyXMLDocument(name, val)
End Property
And after that, this works and equivalent to the code shown above:
obj("foo") = "New value"
MsgBox obj("foo")
' As well as
obj!foo = "New value"
MsgBox obj!foo
' Or for more complex `name` entries (i.e. with invalid identifier symbols)
obj![foo] = "New value"
MsgBox obj![foo]
Note that you have to add the Attribute Value.VB_UserMemId = 0 in some other editor than the VBA editor that ships with Microsoft Office, as that one hides Attribute directives for some reason.. You can easily export the module, open it in notepad, add the directives, and import it back in the VBA editor. As long as you don't change too much with the default member, the directive should not be removed (just make sure you check from time to time in an external editor).
See this other question: Bang Notation and Dot Notation in VBA and MS-Access
The bang operator (!) is shorthand for
accessing members of a Collection or
other enumerable object
If you make your class extend the Collection class in VBA then you should be able to take advantage of those operators. In the following question is an example of a user who extended the collection class:
Extend Collections Class VBA