Re: Cannot call RegisterDataSource on a own datasource

mcben wrote:
> On 4 fév, 14:52, Axel Hecht <[email protected]> wrote:
>> mcben wrote:
>>> On 4 fév, 09:27, Axel Hecht <[email protected]> wrote:
>>>> mcben wrote:
>>>>> Hi folks,
>>>>> Here is quite a long post about a problem with a own datasource
>>>>> implementation based on a xml-datasource.
>>>>> I'm looking for any clues or links that could help me to achieve my
>>>>> first goal : a custom datasource that i could fill from a CSV file.
>>>>> Thanks in advance for reading me :)
>>>>> I'm creating a javascript component that fetches a CSV file with
>>>>> XMLHttpRequest, parses it, then adds lines as RDF resources in a RDF
>>>>> datasource.
>>>>> Its contractid is like "@mozilla.org/rdf/datasource;1?name=mydatasource"
>>>>> so as to get it in the chrome with the "rdf:mydatasource" keyword.
>>>>> I started this work by using an in-memory-datasource as the __proto__
>>>>> properties of my javascript prototype.
>>>>> I could fetch my file and appends data in the datasource : the result
>>>>> was shown in a rdf tree.
>>>>> The first problem with this design was that i was not able to overwrite
>>>>> some nsIRDFDataSource methods (not a real problem in fact), nor extends
>>>>> the in-memory-datasource component with other interfaces : the QI method
>>>>> of my component was never called, so i got a NS_ERROR_NO_INTERFACE
>>>>> error, when i QI another interface (eg: nsIDOMListener to adds
>>>>> XMLHttpRequest callback in my chrome).
>>>>> Then i took a look a the rdf:localstore C++ implementation
>>>>> (nsLocalStore.cpp) and i'm quite happy with its design : it works like a
>>>>> wrapper around a xml-datasource. It "justs" load data from
>>>>> localstore.rdf in the profile directory or creates it if it does not exist.
>>>>> Then with that, I could even read and store a cached version of my CSV
>>>>> file on disk.
>>>>> So, I've made the same design in my javascript component, all
>>>>> nsIRDFDataSource related methods are forwarded to a "mInner"
>>>>> xml-datasource property.
>>>>> But when i try to call RegisterDataSource to register my datasource in
>>>>> the constructor of my component, it throws a NS_ERROR_FAILURE :
>>>>> Here is the code :
>>>>> this._loadLocalData();
>>>>> RDF.RegisterDataSource(this, false);
>>>>> this._loadRemoteData();
>>>>> If i log "this" the console service returns me that is an Object.
>>>>> That's the problem ?
>>>>> In fact I get from the chrome : [xpconnect wrapped (nsISupports,
>>>>> nsIRDFDataSource, nsIRDFRemoteDataSource)] after the registration, even
>>>>> if the registration fails.
>>>>> But, the nsIRDFRemoteDatasource Init method is called at every calls
>>>>> from chrome.
>>>>> Maybe the real problem comes from the xml-datasource initialization.
>>>>> The following code is called by the constructor of my component :
>>>>> this.mInner = Components
>>>>>        .classes["@mozilla.org/rdf/datasource;1?name=xml-datasource"]
>>>>>        .createInstance(Components.interfaces.nsIRDFDataSource);
>>>>> var remote = this.mInner
>>>>>        .QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
>>>>> remote.Init(filespec);
>>>>> The "Init" call throws an exception with the following code
>>>>> "0x804b000a". Its related with nsISocketTransport and means
>>>>> STATUS_WAITING_FOR. Ok, why not.
>>>>> Then remote.loaded returns false, and calling remote.Refresh(false)
>>>>> throws a NS_ERROR_FAILURE
>>>>> What is wrong with that ?
>>>>> So i catch this Init exception and get my remote datasource with the RDF
>>>>> Service like this :
>>>>> remote = RDF.GetDataSource(filespec)
>>>>>           .QueryInterface(Components.interfaces.nsIRDFRemoteDataSource)
>>>>> this.mInner = remote
>>>>>           .QueryInterface(Components.interfaces.nsIRDFDataSource);
>>>>> In that case no problem with remote ds, but the RegisterDataSource go on
>>>>> failing.
>>>>> And later, in the chrome, when i call a method or property that is
>>>>> forwarded to the inner, i got back a undefined result.
>>>>> And i cant look any result in my xul tree.
>>>>> I can post the full source code of the component if needed.
>>>> I suspect that it has something to do with your move from an in-memory
>>>> datasource as inner to an rdf/xml as inner. I didn't get why you made
>>>> that move, was that intentional?
>>> Hi Axel,
>>> Thank you for your answer.
>>> To begin, you can grab my component source code here, with the "second
>>> design" implementation (with inner):
>>> http://pastebin.mozilla.org/319272
>>> And the xul tree that should show my results look quite simple :
>>> <tree id="itemtypes-tree" flex="1"
>>>         datasources="rdf:bi-itemtypes" ref="bi:itemtypes-list">
>>>   <treecols>
>>>     <treecol id="col-name" primary="true" label="Name" flex="1"/>
>>>   </treecols>
>>>   <template>
>>>     <treechildren>
>>>       <treeitem uri="rdf:*">
>>>         <treerow>
>>>           <treecell label="rdf:*" />
>>>         </treerow>
>>>       </treeitem>
>>>     </treechildren>
>>>   </template>
>>> </tree>
>>> Hum. yes, the move was partially intentional :
>>>  * My first try with an in-memory datasource was with the instance set
>>> as __proto__ property in the prototype of my component. That is to
>>> say, that it was not with the "inner" design.
>>> The main problem with this design was that i could not extends my
>>> component by implementing other public interface : the QI function of
>>> my component was never called, nor any method that i though they
>>> overrode existing methods of the in-mem. The only thing that i could
>>> improve in this design was the init phase of my component (by filling
>>> in-mem with XMLHttpRequest) nothing else.
>>> Is it normal that with the following code, the QueryInterface method
>>> is never called, that's why i cant implement any other interfaces ? (i
>>> think that the __proto__ QI is called instead).
>>> function myComponentImplementation() {
>>> }
>>> myComponentImplementation.prototype {
>>>     __proto__ : Components.classes["@mozilla.org/rdf/datasource;1?
>>> name=in-memory-datasource"]
>>>                          .createInstance(Components.interfaces.nsIRDFDataSource),
>>>     QueryInterface : function(iid) {
>>>         if (!iid.equals(C_i.nsIDOMEventListener) &&
>>>             !iid.equals(C_i.nsIRDFDataSource) &&
>>>             !iid.equals(C_i.nsIRDFRemoteDataSource) &&
>>>             !iid.equals(C_i.nsISupports))
>>>             throw Components.results.NS_ERROR_NO_INTERFACE;
>>>         ConsoleService.logStringMessage("QI called:" + iid);
>>>         return this;
>>>     }
>>> }
>>>  * With the "inner" design, i immediatly use a xml-datasource, just
>>> like the nsLocalStore implementation. With that, i could load a cached
>>> version of the rdf file from disk, and then update it with
>>> XMLHttpRequest only if it really needed.
>>> Since, you are thinking that the problem can come from the xml-
>>> datasource, i took the same component, and just replaced the xml-
>>> datasource inner, with an in-memory-datasource.
>>> Indeed, it seems there is no major failure with initialization, i can
>>> register the datasource, but the content that i downloaded with
>>> XMLHttpRequest and that i put in the ds is not reflected in my chrome
>>> xul tree, nor i can query my datasource for any target that sould
>>> exists.
>>> More precisely, about any errors, i had to create the container (the
>>> one to wich I append downloaded resources) with this.mInner (the in-
>>> mem ds) and not my component. Is it normal ?
>>> Look:
>>> this._container = RDFContainer.MakeSeq(this.mInner,
>>> RDF.GetResource(this._struct.ref));
>>> Even though my component should implement nsIRDFDataSource, that's why
>>> i thought i could do that :
>>> this._container = RDFContainer.MakeSeq(this,
>>> RDF.GetResource(this._struct.ref));
>>> But it seems that append does not work anyway.
>>> * Finally, why I made the move to xml-datasource ?
>>> (I thought) I could parse a local rdf file at init, and flushes the
>>> modified results at destruction. I even could observe the download
>>> progress from chrome (eg: with a progressbar), etc.
>>> So any clue ?
>>> What do you think is the best implementation ?
>>> The first design could be perfect if i could override and extends
>>> methods and interfaces of the __proto__ instance.
>>> Thank you for reading me.
>> I suspect that something in your implementation is broken. There ishttp://developer.mozilla.org/en/docs/Aggregating_the_In-Memory_Dataso...,
>> but that hasn't been maintained in years, same goes for its sibling
>> documents.
> 
> Yes, i know this document, and tried some months ago to agregate a xml-
> datasource (for another project) and gave up when i saw that xml-
> datasource cant be aggregated ;-)
> 
> Maybe i should give another try with the in-mem datasource.
> 
> But can you confirm me that i could try that with a javascript
> implementation ?
> 
> 
>> Sorry, no better idea, maybe if you post parts of your code there's
>> better chances.
> 
> Héhé. The whole component is too long / time consuming for you to take
> a look ?
> I understand.
> 
> So first question, that i previously asked. WIth a component
> implementation below, is it normal that I cant override public methods
> of the __proto__. In fact, I can only add private method, that cant be
> accessed by the chrome ?
> 
> function myComponentImplementation() {
> }
> 
> myComponentImplementation.prototype {
>     __proto__ : Components.classes["@mozilla.org/rdf/datasource;1?
> name=in-memory-datasource"]
>                          .createInstance(Components.interfaces.nsIRDFDataSource),
> 
>     QueryInterface : function(iid) {
>         if (!iid.equals(C_i.nsIDOMEventListener) &&
>             !iid.equals(C_i.nsIRDFDataSource) &&
>             !iid.equals(C_i.nsIRDFRemoteDataSource) &&
>             !iid.equals(C_i.nsISupports))
>             throw Components.results.NS_ERROR_NO_INTERFACE;
>         ConsoleService.logStringMessage("QI called:" + iid);
>         return this;
>     }
> 
> }

That is more of a js/xpconnect question. Trying

function A(){this.bar=3;}
function B(){this.__proto__ = new A();this.foo=6};
b=new B()
[object Object]
props(b)
Fields: foo
Fields of prototype: bar
Methods of prototype of prototype of prototype: extend
b.bar
3
b.foo
6

makes me think that you should set the __proto__ to a new instance of 
the in-mem ds in the Constructor. Which makes sense, as you don't want 
to share the in-mem ds across all instances of 
myComponentImplementation, right?

But I guess for real questions on this, you should try .js-engine.

Axel