asp.net-web-api - oData $count 不适用于 Web api 4 中的 EntitySetController

Question

我正在使用 EntitySetController 创建一个 oData Web API Controller ，除了获取总记录数之外，一切正常。

Controller 定义如下:

public class MyODataController : EntitySetController<Entity1, int> where TEntity : class
{
    public override IQueryable<Entity1> Get()
    {
        return EntityDatabase.Get();
    }
}

当我通过以下方式调用计数时:

http://localhost:44789/oData/MyOData/$count

我收到错误:检测到无效操作。 “$count”不是可以绑定(bind)到“Collection([Entity1 Nullable=False])”的操作。

Answer 1

不幸的是，Web API 尚不支持开箱即用的 $count，尽管在未来的版本中应该会支持。同时，您仍然可以通过定义这些类来添加支持:

public class CountODataRoutingConvention : EntitySetRoutingConvention
{
    public override string SelectAction(ODataPath odataPath, HttpControllerContext controllerContext, ILookup<string, HttpActionDescriptor> actionMap)
    {
        if (controllerContext.Request.Method == HttpMethod.Get && odataPath.PathTemplate == "~/entityset/$count")
        {
            if (actionMap.Contains("GetCount"))
            {
                return "GetCount";
            }
        }
        return null;
    }
}

public class CountODataPathHandler : DefaultODataPathHandler
{
    protected override ODataPathSegment ParseAtEntityCollection(IEdmModel model, ODataPathSegment previous, IEdmType previousEdmType, string segment)
    {
        if (segment == "$count")
        {
            return new CountPathSegment();
        }
        return base.ParseAtEntityCollection(model, previous, previousEdmType, segment);
    }
}

public class CountPathSegment : ODataPathSegment
{
    public override string SegmentKind
    {
        get
        {
            return "$count";
        }
    }

    public override IEdmType GetEdmType(IEdmType previousEdmType)
    {
        return EdmCoreModel.Instance.FindDeclaredType("Edm.Int32");
    }

    public override IEdmEntitySet GetEntitySet(IEdmEntitySet previousEntitySet)
    {
        return previousEntitySet;
    }

    public override string ToString()
    {
        return "$count";
    }
}

在 MapODataRoute 中注册它们:

IList<IODataRoutingConvention> routingConventions = ODataRoutingConventions.CreateDefault();
routingConventions.Insert(0, new CountODataRoutingConvention());
config.Routes.MapODataRoute("OData", "odata", GetModel(), new CountODataPathHandler(), routingConventions);

并在您的 Controller 中添加此方法:

public HttpResponseMessage GetCount(ODataQueryOptions<TEntity> queryOptions)
{
    IQueryable<TEntity> queryResults = queryOptions.ApplyTo(Get()) as IQueryable<TEntity>;
    int count = queryResults.Count();
    HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
    response.Content = new StringContent(count.ToString(), Encoding.UTF8, "text/plain");
    return response;
}

为了避免将 GetCount() 复制到每个 Controller ，您可以定义一个从定义 GetCount 的 EntitySetController 派生的基类。