Hi, 2012-10-16 11:03, Vincent Massol skrev: > Hi Andreas, > > It would be great if you could explain your real use case and the reason you > wish to introduce this (I guess you have a use case where you need this :)).
I want to put authorization information in the execution context, and I want to trust that this information is carried over to any new execution context that is activated in the scope of the current request. It is also great if the object that holds the information cannot be replaced. So, if you look at the code you will see that I have implemented a rather aggressive enforcment of the combination of the attributes read-only and inherited. But also, the need for the inherited property already exists for managing the properties "xwikicontext" and "velocityContext". Just look at the TODO and FIXME in DefaultExecutionContextManager in the master branch. But the general idea is just to be able to associate any kind of metadata with each property. It can be compared to how interpreted languages handle variables. Take for instance bash, where you can just set a variable to a value, wich implicitly declares the variable. But you can also explicitly declare a variable, and in the declaration you can provide flags that sets various attributes of the variable. (e.g, declare -r variable='readonly value'.) > See below. > > On Oct 12, 2012, at 9:27 AM, Andreas Jonsson <[email protected]> wrote: > >> Hi everyone, >> >> I would like to propose to introduce a possibility to associate >> properties in the execution context with metadata by declaring them. We >> introduce the class 'ExecutionContextProperty' that will store the >> metadata attributes, in addition to the actual property value. >> >> /** >> * Declare a property in the execution context. >> * >> * @param key The key that names the property >> * @param property The property to declare. >> */ >> public void declareProperty(String key, ExecutionContextProperty property) > Does this mean the current ExecutionContext.setProperty() method would be > deprecated/removed? > > Why not use instead: setProperty(String key, ECP property)? Setting and declaring a property are completely different concepts. In a purely declarative model, properties would have to be declared before being set. But what I'm proposing is more in line with what bash does with variables. Setting a value on an undefined property will implicitly declare it with default values for all attributes. You can also provide an initial value when declaring the property (which of course is required for read-only properties). >> The metadata governs how the property should be treated when managing >> the execution contexts. For instance, these attributes could be supported: >> >> * Read-only - The value may not be updated within the the execution >> context. > How do you ensure this? So getProperty() would continue to return the value > and not an ECP instance right? Yes, getProperty returns the value of the property. I have not added any method to obtain the declared ECP instance as I don't see any need for it right now. Of course, it is only the reference to the value that is guaranteed to be read-only by the execution context. Depending on the application, it may be desirable to make the object immutable, but that is not up to the execution context to enforce. > > So when the user calls declareProperty() with the same key as an existing key > it would be refused if it's been declared Readonly? A property may only be declared once in an execution context, so it will be refused if the property is already declared. It doesn't matter if it was an explicit or implicit declaration. Attempting to declare an already existing property is an indication that something is wrong, so raising an exception seems appropriate. If the property is read-only, then also setProperty will refuse to replace the value. > Now imagine that I pass an ECP instance with a value of List. How do you > prevent some from doing: getProperty("mylistkey").add(somenewelement)? > >> * Inherited - The property will be inherited from the current context >> when replacing the execution context within the scope of a request. > I don't understand this one, we create a new Execution Context for each > Request. No, you are mistaken. We allow the creation and activation of several execution contexts per request. That's why we have the kludges in DefaultExecutionContextManager for copying and cloning "xwikicontext" and "velocityContext". >> * Clone - Also clone the value when the execution context is cloned. > What are the cases when we don't want to clone a property? I don't see any, > for me we always want to clone them and in practice we would instead need to > change our current signature to: > > setProperty(String key, Cloneable value) I do not want to clone my authorization data. It wouldn't hurt cloning it, but it would serve no purpose. But I can also imagine that some applications might want to put objects that are expensive to clone in the execution context. >> * Type - The class of the value, for typechecking when replacing >> the value. > Can you explain more? Does it mean you wish that getProperty() returns a > typed value? We can already do this by using generics. No, it just means that we can perform run-time type checking when setting the value of a declared property. It would catch some errors earlier, but not as early as compile time. >> * Non-null - The value may not be null >> >> So, the arguments for this proposal are at least two: >> >> 1. Catch errors early and simplify debugging. > Can you explain more this point, I don't see the benefit over what we can > already do. You can let the execution context provide some basic validation when setting it. If you mark a value read-only, you will not need to worry about if any component suddenly replaces or remove it in the middle of the request. >> 2. Convenience of having properties automatically maintained across >> execution contexts within the same request cycle. > This is probably related to the inherit item which I don't understand. Yes it is. ;) >> What do you think? > Honestly I don't see the need for this. > > What we lack IMO is proper Execution Context cloning and for this to happen > we need to ensure we only cloneable items in the EC. As for the other "types" > I don't really see a strong need but maybe I've misunderstood a few things > (hence my questions above). > >> I would like to implement and merge this ASAP. > We need to be very careful because the EC is a key class and introducing this > means we're changing an important public API and we cannot go back easily > (except through some deprecation cycles). IMO, seen the importance this > should be a VOTE instead of a PROPOSAL. The proposal adds two methods and one class, while beeing backwards compliant with current code. To me it seems that we have plenty of time to change our minds before releasing 4.3-rc1 if I were to merge this with master right now. Or is our policy that we have to commit to any API that we have added in a milestone release? I will propose a vote for it later in any event. Best Regards, /Andreas > > We would really need some feedback from several devs before going on with > this IMO. ATM I'd like to understand it more before voting. > > Thanks > -Vincent > > PS: Didn't get the time to read your implementation code yet > >> Best Regards, >> >> /Andreas > _______________________________________________ > devs mailing list > [email protected] > http://lists.xwiki.org/mailman/listinfo/devs > _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
