Background
OData supports three metadata levels for the JSON format, namely –
- No Metadata
- Minimal Metadata
- Full Metadata
No Metadata as the name suggests does not include control information other than nextLink and count. Minimal metadata responses usually include context, etag, deltalink etc. whereas full metadata responses contain all the control information like navigationLink, assciationLink, readLink, mediaReadLink etc.
ODataMetadataSelector
With odata.net >=7.6.1, it will be possible to customize what metadata gets written out. A new class, ODataMetadataSelector is introduced which exposes methods that can be overridden to add or remove control information related to the navigation properties, stream properties, and operations.
public virtual IEnumerable<IEdmOperation> SelectBindableOperations(IEdmStructuredType type, IEnumerable<IEdmOperation> bindableOperations) { // Select bindable operations return bindableOperations; } public virtual IEnumerable<IEdmNavigationProperty> SelectNavigationProperties(IEdmStructuredType type, IEnumerable<IEdmNavigationProperty> navigationProperties) { // Select the navigation properties from the type return navigationProperties; } public virtual IEnumerable<IEdmStructuralProperty> SelectStreamProperties(IEdmStructuredType type, IEnumerable<IEdmStructuralProperty> selectedStreamProperties) { // Select the streamProperties from the type return selectedStreamProperties; }
The instance of this class can be set on ODataMessageWriterSettings’s property, MetadataSelector. Since ODataMessageWriterSettings can be dependency injected, you can also use dependency injection for ODataMetadataSelector by injecting a custom ODataMessageWriterSettings.
Since this will get called for every resource being requested, it is highly recommended to cache the results if possible.
Usage Example
You can choose to annotate properties of types for which you don’t want to write out the metadata. This sample here will omit control information for all such navigation properties. You can also have arbitrary criteria to select the metadata such as omitting all actions.
public class SampleMetadataSelector : ODataMetadataSelector { private IEdmModel model; private IDictionary<IEdmVocabularyAnnotatable, bool> annotationCache; public SampleMetadataSelector(IEdmModel model, IDictionary<IEdmVocabularyAnnotatable, bool> cache) { this.model = model; this.annotationCache = isHiddenDictionary; } public override IEnumerable<IEdmNavigationProperty> SelectNavigationProperties(IEdmStructuredType type, IEnumerable<IEdmNavigationProperty> navigationProperties) { return navigationProperties.Where(s => { if (!isHiddenCache.ContainsKey(s)) { IEdmVocabularyAnnotation annotation = model.FindVocabularyAnnotations<IEdmVocabularyAnnotation>(s, "AnnotationName").FirstOrDefault(); annotationCache[s] = annotation == null; } return annotationCache[s]; } ); } public override IEnumerable<IEdmOperation> SelectBindableOperations(IEdmStructuredType type, IEnumerable<IEdmOperation> bindableOperations) { //Omit all actions return bindableOperations.Where(f => f.SchemaElementKind != EdmSchemaElementKind.Action); } }
Can you please suggest what is advantage of using 7.6 in compare with 6.15 library. We are using 6.15 library and facing some performance issue.
If we migrate to latest library , will we get performance advantage?