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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Query redesign","articleBody":"This is a proposal for a redesign for the query API. It allows a directive to find other directives that are structurally its 'children'.\n- A directive can query the children of the element it is placed on with `@ContentChild` / `@ContentChildren` (used to be @Query) and its view with `@ViewChild` / `@ViewChildren` (used to be @ViewQuery).\n- When using @xxxChild the object received will be the desired element (or null if not found), when using @xxxChildren the object will be an ObservableArray.\n- Queries will be recalculated when a structural change occurs (ng-if, ng-for), @xxxChild will be set to the new value, while @xxxChildren will notify via the observable API.\n- The results will not be injectable, but rather set on declared properties by the framework.\n\nEx:\n\n``` javascript\n@Component(...)\n@View(...) \nclass ListComponent {\n  @ContentChild(ItemDirective)\n  itemDirective: ItemDirective;\n }\n\n@Component(...)\n@View(...) \nclass ListComponent2 {\n  @ViewChildren(ItemDirective)\n  itemDirectives: ObservableArray\u003cItemDirective\u003e;\n }\n```\n\nThe children directives will be set before the following callbacks are fired (https://github.com/angular/angular/issues/3863) - `afterContentChecked` for `ContentChild` and  `afterViewChecked` for `ViewChild`. \n\nBoth query mechanisms do not go into further into component subviews. `ContentChild / ContentChildren` support configurable visibility as follows :\n- `descendants: true` - all content descendants are considered\n- `descendants: false` - only direct children of the querying directive are considered (default)\n  `ViewChildren` has no visibility configuration. Queries always skip the element on which the querying directive lives (similar to `DOM.querySelector`).\n\nImplementation\n- [x] implement lifecycle hooks (https://github.com/angular/angular/issues/3863)\n- [x] hook up query update calls to the new hooks\n- [x] add integration test for view query with var bindings (#3920)\n- [x] remove query from forms API (#3962)\n- [x] using view.elementInjectors internally instead of inj.children tree (closes #3625)\n- [x] add `ContentChildren` and `ViewChildren` (#4237)\n- [x] use Rx.Next for ObservableArray\n- [x] move declaration to @Component field and using setters\n- [x] implement ContentChild and ViewChild\n- [x] remove self visibility from Query \n- [ ] optimize static single child\n- [x] implement dynamic strategy for queryRefs\n\n// cc @mhevery @vsavkin \n","author":{"url":"https://github.com/rkirov","@type":"Person","name":"rkirov"},"datePublished":"2015-08-31T22:41:37.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/3922/angular/issues/3922"}