collection watches are not working #31

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1. tbosch

   added

   type: bug

   on May 2, 2014
2. tbosch

   assigned

   caitp

   on May 2, 2014
3. caitp commented on May 6, 2014

   

   caitp

   on May 6, 2014

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   So I was investigating this yesterday and over the weekend, and what I'm finding is that CollectionAST(FieldReadAST(ContextReferenceAST)) works well, but FieldReadAST(ContextReferenceAST) doesn't (because a CollectionAST handler never does anything).

   So, this is the issue we have with a dynamic language like javascript -- we don't know in advance that a particular field must contain a List (or something), it might initially be undefined, and then turn into a list, and then turn into a string, or whatever.

   Because of this, there are only really 2 options, I think:

   1. something similar to $watchCollection which will make sure to set up the CollectionAST node, even if the value isn't a collection at the time of parsing

   2. totally scrap the strategy based on a more statically typed language, and do something more dynamic --- let a particular field's handlers change at runtime, and support reporting change between non-collection to collection and vice versa.

   I think option 2) could hurt performance a fair bit, but I don't really have a measure of the performance cost.

   However, neither of the situations I mentioned have anything to do with 9417cd4 as far as I can tell, so you may be reproducing the issue differently. Can you show a test case?
4. tbosch commented on May 6, 2014

   

   tbosch

   on May 6, 2014

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   Hi,
   the problem is when the collection reference changes. Here is a test (to be put into watchgroups.spec.js):

     describe('collections', function() {
       iit('should watch collections if their reference changes', ()=>{
         setup({'a': [1]});
         var ast = new CollectionAST(new FieldReadAST(new ContextReferenceAST(), 'a'));
         var watch = watchGrp.watch(ast, logCurrentValue);
         watchGrp.detectChanges();
         logger.clear();
   
         context.a = [2];
         watchGrp.detectChanges();
         expect(logger._list[0].iterable).toEqual([2]);
       });
     });
   
5. caitp commented on May 9, 2014

   

   caitp

   on May 9, 2014

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   @mhevery what was the strategy in Dart for handling this? The problem is that the DirtyCheckingRecord with the CollectionHandler is the first thing which is dirty checked, so its internal copy of the array still references the old array (because the FieldRead handler hasn't done its work yet)

   There are lots of ways around this, but I want to make sure it's in sync with the dart implementation.