The QueryView and EntityView both serve the purposes of presenting data from the cache to the view model, and providing reference counting. A DataView is created from the createView method of a QueryCache or EntityCache:
\Client\Data\MasterDetailBrowse\ViewModels\MasterViewModels.ts
this._websitesQueryView = dataContext.masterDetailBrowseSample.websitesQuery.createView(container);In the sample above, the container object acts as a lifetime object. Lifetime objects inform the cache when a given view is currently being displayed on the screen. This allows the shell to make several adjustments for performance:
- Adjust polling interval when the part is not on the screen
- Automatically dispose of data when the blade containing the part is closed
Creating a DataView does not result in a data load operation from the server. The server is only queried when the fetch operation of the view is invoked:
\Client\Data\MasterDetailBrowse\ViewModels\MasterViewModels.ts
public onInputsSet(inputs: any): MsPortalFx.Base.Promise {
return this._websitesQueryView.fetch({ runningStatus: inputs.filterRunningStatus.value });
}The runningStatus is a filter which will be applied to the query. This allows several views to be created over a single cache, each presenting a potentially different data set.
In many cases, you may want to shape your data to fit the view you are binding to. There are many cases where this is useful:
- Shaping data to match the contract of a control (data points of a chart, for instance)
- Adding a computed property to a model object
- Filtering data on the client based on a property
The recommended approach to these cases is to use the map and filter methods found in the Knockout projections library, included in the SDK.
See Shaping and filtering your data for more details.