我们可以在 olingo odata 中创建最多 3 个段的导航属性吗

Question

我有一个要求，我们需要在 URI 中发送 3 个实体集

例如，{serviceRoot}/Entity1('ID')/Entity2('ID')/Entity3

我已经浏览了 olingo git 存储库，但只能找到 2 个片段（对于 3 个片段 Not Implemented Exception 被抛出。

我想了解 URL({serviceRoot}/Entity1('ID')/Entity2('ID')/Entity3) 是否有效？

Olingo 使用的版本是 4.5

Answer 1

从 OData Sepcifiion 的角度来看，拥有 3 级甚至 n 级都很好 'navigation properties'，URL 的第一段是实体或实体集，然后您将必须创建导航属性，这些属性绑定到（读取return）和实体集或实体。

你得到 Not Implemented Exception 异常的原因是，如果你通读 readEntityCollection 的代码，你会发现下面的片段

if (segmentCount == 2){ //navigation: e.g. DemoService.svc/Categories(3)/Products

此处检查该段是否为第 3 部分并将其视为导航属性但如果您更深入，它只是有一个 else 条件，它会抛出异常。

为了实现您的目的，您必须在代码中实现此逻辑才能更深入一个（或更多）级别

下面是完整代码供参考

public void readEntityCollection（ODataRequest 请求，ODataResponse 响应，UriInfo uriInfo，ContentType responseFormat）抛出 ODataApplicationException，SerializerException {

EdmEntitySet responseEdmEntitySet = null; // for building ContextURL
EntityCollection responseEntityCollection = null; // for the response body

// 1st retrieve the requested EntitySet from the uriInfo
List<UriResource> resourceParts = uriInfo.getUriResourceParts();
int segmentCount = resourceParts.size();

UriResource uriResource = resourceParts.get(0); // the first segment is the EntitySet
if (! (uriResource instanceof UriResourceEntitySet)) {
    throw new ODataApplicationException("Only EntitySet is supported", HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(),Locale.ROOT);
}

UriResourceEntitySet uriResourceEntitySet = (UriResourceEntitySet) uriResource;
EdmEntitySet startEdmEntitySet = uriResourceEntitySet.getEntitySet();

if(segmentCount == 1){ // this is the case for: DemoService/DemoService.svc/Categories
    responseEdmEntitySet = startEdmEntitySet; // first (and only) entitySet

    // 2nd: fetch the data from backend for this requested EntitySetName
    responseEntityCollection = storage.readEntitySetData(startEdmEntitySet);
}else if (segmentCount == 2){ //navigation: e.g. DemoService.svc/Categories(3)/Products
    UriResource lastSegment = resourceParts.get(1); // don't support more complex URIs
    if(lastSegment instanceof UriResourceNavigation){
        UriResourceNavigation uriResourceNavigation = (UriResourceNavigation)lastSegment;
        EdmNavigationProperty edmNavigationProperty = uriResourceNavigation.getProperty();
        EdmEntityType targetEntityType = edmNavigationProperty.getType();
        responseEdmEntitySet = Util.getNavigationTargetEntitySet(startEdmEntitySet, edmNavigationProperty);

        // 2nd: fetch the data from backend
        // first fetch the entity where the first segment of the URI points to
        // e.g. Categories(3)/Products first find the single entity: Category(3)
        List<UriParameter> keyPredicates = uriResourceEntitySet.getKeyPredicates();
        Entity sourceEntity = storage.readEntityData(startEdmEntitySet, keyPredicates);
        // error handling for e.g.  DemoService.svc/Categories(99)/Products
        if(sourceEntity == null) {
            throw new ODataApplicationException("Entity not found.", HttpStatusCode.NOT_FOUND.getStatusCode(), Locale.ROOT);
        }
        // then fetch the entity collection where the entity navigates to
        responseEntityCollection = storage.getRelatedEntityCollection(sourceEntity, targetEntityType);
    }
}else{ // this would be the case for e.g. Products(1)/Category/Products
    throw new ODataApplicationException("Not supported", HttpStatusCode.NOT_IMPLEMENTED.getStatusCode(),Locale.ROOT);
}
    // 3rd: create and configure a serializer
    ContextURL contextUrl = ContextURL.with().entitySet(responseEdmEntitySet).build();
    final String id = request.getRawBaseUri() + "/" + responseEdmEntitySet.getName();
    EntityCollectionSerializerOptions opts = EntityCollectionSerializerOptions.with().contextURL(contextUrl).id(id).build();
    EdmEntityType edmEntityType = responseEdmEntitySet.getEntityType();

    ODataSerializer serializer = odata.createSerializer(responseFormat);
    SerializerResult serializerResult = serializer.entityCollection(this.srvMetadata, edmEntityType, responseEntityCollection, opts);

    // 4th: configure the response object: set the body, headers and status code
    response.setContent(serializerResult.getContent());
    response.setStatusCode(HttpStatusCode.OK.getStatusCode());
    response.setHeader(HttpHeader.CONTENT_TYPE, responseFormat.toContentTypeString());   
}

Answer 2

给出答案，总之没有段数限制， {service Root}/Entity 1.12=])/Entity 2('ID')/Entity3) 是有效的，Shiva

很好地解释了其余部分

我们可以在 olingo odata 中创建最多 3 个段的导航属性吗

Can we create navigation properties upto 3 segments in olingo odata

odata

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