Class StreamFallback

A DataSource that returns the first stream which has content

The StreamFallback DataSource is part of the Standard EAV Data Sources. It will pass on the first stream which has results. The order of evaluation is based on the names of the streams as they enter the StreamFallback.

How to use with the VisualQuery

When using the VisualQuery you can just drag it into your query. This is what it usually looks like:

The above example shows a query from the blog app:

  1. a stream-fallback with 4 in-streams
  2. the first stream which would filter by tag, if the URL had a tag in it - as the test-data has no tag, this stream delivers no results
  3. the second stream filters by author - as the url would have an author (specified in the test-values), it does return items

The StreamFallback therefor passes on the items provided by the author-filter. Note that while using the VisualQuery, all other streams are also processed to show what's happening. At runtime it will stop processing other streams once it's found a first match.

Programming With The StreamFallback DataSource

We recommend to use the VisualQuery where possible, as it's easier to understand and is identical for C# and JavaScript. It's also better because it separates data-retrieval from visualization.

Read also

You should find some examples in this demo App

History

  1. Introduced in EAV 3.x, 2sxc ?

API Documentation

Inheritance
System.Object
HasLog
DataSourceBase
StreamFallback
Inherited Members
Namespace: ToSic.Eav.DataSources
Assembly: ToSic.Eav.DataSources.dll
Syntax
[PublicApi_Stable_ForUseInYourCode]
[VisualQuery(NiceName = "Stream Fallback", UiHint = "Find the first stream which has data", Icon = "call_merge", Type = DataSourceType.Logic, GlobalName = "ToSic.Eav.DataSources.StreamFallback, ToSic.Eav.DataSources", DynamicOut = false, DynamicIn = true, HelpLink = "https://r.2sxc.org/DsStreamFallback")]
public sealed class StreamFallback : DataSourceBase, IDataSource, IAppIdentity, IZoneIdentity, IAppIdentityLight, ICacheInfo, ICacheKey, ICacheExpiring, ITimestamped, ICanPurgeListCache, IHasLog, IDataTarget, IDataPartShared
Remarks

Technically many things could just identify the app they belong to, and let the system look up the zone. But this would be inefficient, so for optimization, many items identify themselves with both the app and zone Ids

Implements