如何使用"SelectMany"使用DataServiceQuery<> [英] How to use "SelectMany" with DataServiceQuery<>

问题描述

我有下面的DataServiceQuery反对ADO数据服务运行(已安装更新以使其像.net 4一样运行):

I have the following DataServiceQuery running agaist an ADO Data Service (with the update installed to make it run like .net 4):

 DataServiceQuery<Account> q = (_gsc.Users
            .Where(c => c.UserId == myId)
            .SelectMany(c => c.ConsumerXref)
            .Select(x => x.Account)
            .Where(a => a.AccountName == "My Account" && a.IsActive)
            .Select(a => a)) as DataServiceQuery<Account>;

我在运行它时遇到一个例外:无法在单个资源上指定查询选项(orderby，where，take，skip)

When I run it, I get an exception: Cannot specify query options (orderby, where, take, skip) on single resource

据我所知，我需要使用"SelectMany"版本，其中包括一个附加的lambda表达式( http://msdn.microsoft.com /en-us/library/bb549040.aspx )，但我无法使其正常工作.

As far as I can tell, I need to use a version of "SelectMany" that includes an additonal lambda expression (http://msdn.microsoft.com/en-us/library/bb549040.aspx), but I am not able to get this to work correctly.

有人可以告诉我如何正确组织"SelectMany"呼叫吗?

Could someone show me how to properly structure the "SelectMany" call?

谢谢您的帮助.

推荐答案

Data Services不支持将SelectMany与后续的Select组合在一起，除非您包括一个键选择器以将"Many"过滤回仅一项.

Data Services doesn't support composing SelectMany with a subsequent Select unless you include a key selector to filter the 'Many' back to just one item.

如果您以URI的方式考虑查询，您将理解原因.

If you think about queries in terms of URIs you will understand why.

在OData URI中，在导航之前，您只需拥有一个实体(即/NavigationProperty).

In OData URIs you have to have just one Entity before you navigate (i.e. /NavigationProperty).

所以这个:

~/Users(123)/ConsumerXRef

可以，因为在检索许多相关的ConsumerXRef之前，您有一个用户(123).

is okay because you have one User (123) before you retrieve the many related ConsumerXRef(s).

但是这不好:

~/Users(123)/ConsumerXRef/Account

因为在导航到帐户之前您没有识别出单个ConsumerXRef.

because you don't identify a single ConsumerXRef before navigating to accounts.

当您将这种想法带入LINQ领域时，将发生以下情况:

When you take this thinking into LINQ land, something like this:

from u in ctx.Users
where u.ID == 123
from c in u.ConsumerXRef
select c;

可以，因为它可以大致翻译为:

is okay because it roughly translates to:

~/Users(123)/ConsumerXRef

但是这个:

from u in _gsc.Users
where u.UserId == myId
from c in u.ConsumerXref
where c.AccountName == "MyAccount" && c.IsActive
select x.Account;

不好，因为-我猜在这里-AccountName不是关键吗?所以这会翻译成类似该网址的内容

is no good because - I'm guessing here - AccountName isn't the key? so this translates to something like this URL

~/Users(123)/ConsumerXRef/Account/?$filter=AccountName eq 'MyAccount' ...

这是无效的，因为您没有先选择特定的ConsumerXRef即可浏览(从ConsumerXRefs到他们的帐户).

which is invalid because you've navigated (from ConsumerXRefs to their Accounts) without first selecting a specific ConsumerXRef.

这有意义吗?

希望如此

亚历克斯

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