如何定义一个可选的导航属性（？$展开;）在code？ [英] How does one define an (optional) navigation property (?$expand=) in code?

问题描述

首先，解释和要点，那么问题。所以：

First the explanation and the gist, then the question. So:

比方说，我有一个观点 AccountView 在EF定义（6.1.1）数据库第一（EDMX），以便code生成的类是

Let's say I have a view AccountView defined in EF (6.1.1) database first (edmx) so that the code-generated class is

//This class is generated from a view by EF (edmx)...
public partial class AccountView
{
    public System.Guid Id { get; set; }
    public int CompanyId { get; set; }
}

然后，我创建了相同的命名空间部分类（实体）的

[MetadataType(typeof(AccounViewMetaData))]
public partial class AccounView
{
    //This is added here explicitly. AccountView itself exposes just
    //a naked key, CompanyId.
    public virtual Company Company { get; set; }

    //This is just in case...
    public class AccounViewDomainMetaData
    {
        //This is to add a navigation property to the OData $metadata. How to do this
        //in WebApiConfig? See as follows...
        [ForeignKey("Company")]
        public int CompanyId { get; set; }
    }
}

和

//This is an EF generated class one from an edmx..-
public partial class Company
{
    public Company()
    {            
    }

    public int CompanyID { get; set; }
    public string Name { get; set; }
}  

然后在 WebApiConfig 我写，或尝试，在OData的V4的东西（最新，6.9.0.0系列的WebAPI，最新的也有）如下：

And then in WebApiConfig I Write, or try to, something in OData v4 (the newest, 6.9.0.0 series with WebApi, the newest also) as follows

builder.EntitySet<Entities.Company>("Companies");

var accountSet = builder.EntitySet<Entities.AccountView>("Accounts");
accountSet.EntityType.HasKey(i => i.Id); //EF has hard time recognizing primary keys on database first views...

//TODO: How should I define the required binding so that I could "?$expand=Company"
//as such as ``http://example.com/service/Accounts?$expand=Company``
//accountSet.HasRequiredBinding(i => i.CompanyId, typeof(Entities.Company));

生成的 $元像

<schema>
    <EntityType Name="Company">
        <Key>
            <PropertyRef Name="CompanyID"/>
        </Key>
        <Property Name="CompanyID" Type="Edm.Int32" Nullable="false"/>
        <Property Name="Name" Type="Edm.String"/>
     </EntityType>

    <EntityType Name="AccountView">
        <Key>
            <PropertyRef Name="Id"/>
        </Key>
        <Property Name="Id" Type="Edm.Guid" Nullable="false"/>
        <Property Name="CompanyId" Type="Edm.Int32" Nullable="false"/>
        <NavigationProperty Name="Company" Type="Entities.Company" Nullable="false"/>
    </EntityType>
</Schema>

问题（S）：正如 TODO 评论中提及，我应该如何定义

Question(s): As mentioned in the TODO comment, how should I define

• 的导航属性，这样我可以打电话给 http://example.com/Accounts?$expand=Company 或的http：//例子.COM /账户？$公司？

• A navigational property so that I could call http://example.com/Accounts?$expand=Company or http://example.com/Accounts?$Companies?

现在它的工作原理，如果我称之为

Now it works if I call

• http://example.com/Accounts 或


• http://example.com/Accounts（someId）

• http://example.com/Accounts or
• http://example.com/Accounts(someId)

然后，如果我做这样的事情。

Then if I do something like

• http://example.com/Accounts?$expand=Companies


• http://example.com/Accounts?$expand=Company 或


• http://example.com/Accounts（someId）？$ =拓展公司

• http://example.com/Accounts?$expand=Companies
• http://example.com/Accounts?$expand=Company or
• http://example.com/Accounts(someId)?$expand=Company

我得到映入眼帘的 HTTP 400 （？$展开;公司）或 HTTP 500 （？$ =拓展公司）。

I get greeted by HTTP 400 (?$expand=Companies) or HTTP 500 (?$expand=Company).

我会成功，但创建一个遏制关系了。它看起来像，不过，它需要具有由一个ID定义的根实体，而我想提供GET为根和可选扩展到子榜对象（因此这个问题呢？$ =扩展）

I succeeded with creating a Containment relationship already. It looks like, though, it requires having the root entity defined by an ID, whereas I'd like to provide "GET" to the root and optionally expand to a "child list" objects (hence this question about ?$expand=).

现在的情况是有一个非可选的展开做了一个实体，但我怀疑，我想未来的事情已经是那里的列表的场景实体（或公司在这个具体的例子而言），但我怎么能实现这些场景？如何修复即使这种情况下的扩展应用于第一总是存在的子对象？

Now the case is having one non-optional expand done for one entity, but I suspect the next thing I'd like have is a scenario where there's a list of entities (or companies in terms of this specific example) but how could I achieve these scenarios? How to fix even this case of expanding to the first always existing sub-object?

我的控制器被定义如下

public class AccountsController: ODataController
{
    [EnableQuery]
    public IHttpActionResult Get()
    {
        try
        {
            //This context here is a EF entities model (generated from an edmx)...
            return Ok(Context.AccountView);
        }
        catch(Exception ex)
        {
            return InternalServerError(); 
        }
    }

    [EnableQuery]
    public IHttpActionResult Get([FromODataUri]Guid key)
    {
        try
        {
            return Ok(SingleResult.Create(Context.AccountView.Where(a => a.Id == key)));
        }
        catch (Exception ex)            
        {                
            return InternalServerError(ex); 
        }
    }
}

什么我基本上试图做的是添加一些更多的元数据数据库第一，EDMX，观点和模拟天生的文章<一个href=\"http://www.asp.net/web-api/overview/odata-support-in-aspnet-web-api/using-$select,-$expand,-and-$value\"相对=nofollow>使用$选择，$扩大，并在的ASP.NET Web API的OData 2 $ 的价值。迄今没有成功...

What I'm basically trying to do is to add some more metadata to database first, edmx, views and mimick the article Using $select, $expand, and $value in ASP.NET Web API 2 OData. Thus far with no success...

＆LT;编辑1：越来越复杂了，可以这么说。 HTTP 500错误来自内部异常（我不得不把打破托管框架例外），上面写着

<edit 1: The plot thickens, so to speak. The HTTP 500 error comes from an internal exception (I had to turn on breaking to managed framework exceptions) that says

System.NotSupportedException类型的第一次机会异常出现在EntityFramework.dll

A first chance exception of type 'System.NotSupportedException' occurred in EntityFramework.dll

其他信息：指定的类型成员公司不支持LINQ到实体。只有初始化，实体成员和实体导航属性都支持。

Additional information: The specified type member 'Company' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

所以，是的， AccountView 是一个视图，它没有直接的外键关系公司表（这恰好是一个表，但也可以是一个视图太）。我怎么可能去增加一个？我虽然添加元数据的伎俩已经由 $元信息作为证明。不只是OData的写 INNER JOIN 在数据库中？我失去了一些东西在这里？ ...这似乎与我添加了公司引用和EF不喜欢这样的方式。它看起来我应该去了解它添加到OData的模型仅仅...

So, yes, AccountView is a view and it does not have a direct foreign key relation to Company table (which just happens to be a table, but it could be a view too). How could I go to add one? I though adding metadata did the trick already, as evidenced by $metadata information. Doesn't OData just write an INNER JOIN in the database? Am I missing something here? ... This seem to be related to the way I added the Company reference and EF doesn't like that. It looks I should go about adding it to the OData model only...

＆LT;编辑2：这似乎并没有发挥作用（至少不符合我的设置），如果我更改 AccountView CompanyId 到 CompanyID 相匹配的外壳，在公司定义的表。

<edit 2: It doesn't seem to make a difference (at least not with the setting I have) if I change the AccountView CompanyId to CompanyID to match the casing that of the definition in Company table.

＆LT; EDIT3：我问另外一个相关的问题这一点，<一个href=\"http://stackoverflow.com/questions/27580167/how-to-add-complex-properties-on-a-model-built-with-odataconventionmodelbuilder\">How在从EF模型与ODataConventionModelBuilder建立了一个模型添加复杂的属性。

<edit3: I asked another, related question to this, How to add complex properties on a model built with ODataConventionModelBuilder from an EF model.

推荐答案

这看起来我这人回答为相关的另一篇文章和小从另一个论坛上推。

It looks I got this one answered as to related another post and little pushing from another forum.

关于异常，事实上，它是由该查询击中到数据库并尝试检索它们没有定义的列引起的。欲了解更多信息：

About the exception, indeed, it was caused by the query hitting to the database and trying to retrieve columns which aren't defined there. For more information:

• The指定型部件中不LINQ支持实体。只有初始化，实体成员和实体导航属性都支持


• EF 4：指定类型的成员'*'在LINQ是不支持的实体

• The specified type member is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported
• EF 4: The specified type member '*' is not supported in LINQ to Entities

然后作为code和答案，另一个问题是，<一个href=\"http://stackoverflow.com/questions/27535409/expanding-navigation-properties-with-odataqueryoptions/27603462#27603462\">Expanding导航性能与ODataQueryOptions 。在code有点这里增加如下：

Then as for the code and answer, the other question is Expanding navigation properties with ODataQueryOptions. The code a bit augmented here is as follows

public async Task<IHttpActionResult> Get(ODataQueryOptions<T> options)
{
    IQueryable<T> tempQuery = Context.AccountView;
    IQueryable<T result = tempQuery;

    if(options.SelectExpand != null)
    {
        if(options.Filter != null)
        {
            tempQuery = options.Filter.ApplyTo(tempQuery, new ODataQuerySettings()) as IQueryable<T>;   
        }
         /* Other options that should go to the DB level... */

        //The results need to be materialized, or otherwise EF throws a
        //NotSupportedException due to columns and properties that aren't in the DB...
        result = (await tempQuery.ToListAsync()).AsQueryable();

        //Do here the queries that can't be hit straight by the queries. E.g.
        //navigation properties not defined in EF views (that can't be augmented)...
        //E.g. get the company here.

        //This is needed to that OData formatter knows to render navigation links too.
        Request.ODataProperties().SelectExpandClause = options.SelectExpand.SelectExpandClause;
}

return Ok(result);

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