c# - 在 OData 中评估 IQueryable 后如何填充模型中的某些属性？

Question

我正在将 OData 与 Entity Framework 结合使用。假设我有以下模型和 Controller 方法:

public class Model1
{
    public int Id { get; set; }
    public int Field2 { get; set; }
    public int FieldFromOtherService { get; set; }
    public Model2 Model2 { get; set; } // Navigation Property
    public int Model2Id { get; set; }
}

public class Model2
{
    public int Id { get; set; }
    public int Field { get; set; }
}


[HttpGet, EnableQuery]
public IQueryable<Model1> Get()
{
    return modelRepository.List();
}

Model1 具有不是从数据库获取的属性 FieldFromOtherService - 它是从其他服务检索的。在应用 OData top、skip、expand 和 select 子句后，我需要一种方法来填充此属性。

有办法实现吗？我尝试对 IQueryable 进行包装并在评估后调用操作，但当查询更复杂时它会崩溃。

Answer 1

最后，我在 @zaitsman 的建议下成功实现了我的目标。这比我想象的更难，因为 OData 添加了不可访问的包装器(类 SelectAllAndExpand、SelectAll、SelectSomeAndInheritance、SelectSome)。当使用expand时，需要从wrapper中提取DTO。我的代码看起来或多或少像这样:

[HttpGet]
public IHttpActionResult Get(ODataQueryOptions<Model1> options)
{
    var result = modelRepository.List();
    Action<ICollection<Model1>> postAction = collection => { Console.WriteLine("Post Action"); };
    return ApplyOdataOptionsAndCallPostAction(result, options, postAction);
}

private IHttpActionResult ApplyOdataOptionsAndCallPostAction<T>(
    IQueryable<T> baseQuery, 
    ODataQueryOptions<T> options, 
    Action<ICollection<T>> postAction)
    where T : class
{
    var queryable = options.ApplyTo(baseQuery);
    var itemType = queryable.GetType().GetGenericArguments().First();
    var evaluatedQuery = ToTypedList(queryable, itemType);

    var dtos = ExtractAllDtoObjects<T>(evaluatedQuery).ToList();
    postAction(dtos)

    return Ok(evaluatedQuery, evaluatedQuery.GetType());
}

private static IList ToTypedList(IEnumerable self, Type innerType)
{
    var methodInfo = typeof(Enumerable).GetMethod(nameof(Enumerable.ToList));
    var genericMethod = methodInfo.MakeGenericMethod(innerType);
    return genericMethod.Invoke(null, new object[]
    {
        self
    }) as IList;
}

private IEnumerable<T> ExtractAllDtoObjects<T>(IEnumerable enumerable)
    where T : class
{
    foreach (var item in enumerable)
    {
        if (item is T typetItem)
        {
            yield return typetItem;
        }
        else
        {
            var result = TryExtractTFromWrapper<T>(item);
            if (result != null)
            {
                yield return result;
            }
        }
    }
}

private static T TryExtractTFromWrapper<T>(object item)
    where T : class
{
    if (item is ISelectExpandWrapper wrapper)
    {
        var property = item.GetType().GetProperty("Instance");
        var instance = property.GetValue(item);
        if (instance is T val)
        {
            return val;
        }
    }

    return null;
}

private IHttpActionResult Ok(object content, Type type)
{
    var resultType = typeof(OkNegotiatedContentResult<>).MakeGenericType(type);
    return Activator.CreateInstance(resultType, content, this) as IHttpActionResult;
}