使用 Web API 和 OData，我有一个服务，它暴露了数据传输对象而不是实体框架实体。
我使用 AutoMapper 将 EF 实体转换为它们的 DTO 对应项，使用
我使用 AutoMapper 将 EF 实体转换为它们的 DTO 对应项，使用
ProjectTo()：public class SalesOrdersController : ODataController
{
private DbContext _DbContext;
public SalesOrdersController(DbContext context)
{
_DbContext = context;
}
[EnableQuery]
public IQueryable<SalesOrderDto> Get(ODataQueryOptions<SalesOrderDto> queryOptions)
{
return _DbContext.SalesOrders.ProjectTo<SalesOrderDto>(AutoMapperConfig.Config);
}
[EnableQuery]
public IQueryable<SalesOrderDto> Get([FromODataUri] string key, ODataQueryOptions<SalesOrderDto> queryOptions)
{
return _DbContext.SalesOrders.Where(so => so.SalesOrderNumber == key)
.ProjectTo<SalesOrderDto>(AutoMapperConfig.Config);
}
}
AutoMapper（V4.2.1）的配置如下，注意 ExplicitExpansion() ，它可以防止在未请求时自动扩展导航属性的序列化：
cfg.CreateMap<SalesOrderHeader, SalesOrderDto>()
.ForMember(dest => dest.SalesOrderLines, opt => opt.ExplicitExpansion());
cfg.CreateMap<SalesOrderLine, SalesOrderLineDto>()
.ForMember(dest => dest.MasterStockRecord, opt => opt.ExplicitExpansion())
.ForMember(dest => dest.SalesOrderHeader, opt => opt.ExplicitExpansion());
ExplicitExpansion()会创建一个新的问题，其中以下请求会引发错误：
EF不知道导航属性/odatademo/SalesOrders('123456')?$expand=SalesOrderLines
URI中指定的查询无效。指定的类型成员“SalesOrderLines”在LINQ to Entities中不受支持。
SalesOrderLines，所以这个错误正是我预期发生的。问题是，我该如何处理这种类型的请求？
ProjectTo()方法有一个重载，允许我传递需要展开的属性数组，我找到并修改了扩展方法ToNavigationPropertyArray，试图将请求解析为字符串数组：[EnableQuery]
public IQueryable<SalesOrderDto> Get([FromODataUri] string key, ODataQueryOptions<SalesOrderDto> queryOptions)
{
return _DbContext.SalesOrders.Where(so => so.SalesOrderNumber == key)
.ProjectTo<SalesOrderDto>(AutoMapperConfig.Config, null, queryOptions.ToNavigationPropertyArray());
}
public static string[] ToNavigationPropertyArray(this ODataQueryOptions source)
{
if (source == null) { return new string[]{}; }
var expandProperties = string.IsNullOrWhiteSpace(source.SelectExpand?.RawExpand) ? new List<string>().ToArray() : source.SelectExpand.RawExpand.Split(',');
for (var expandIndex = 0; expandIndex < expandProperties.Length; expandIndex++)
{
// Need to transform the odata syntax for expanding properties to something EF will understand:
// OData may pass something in this form: "SalesOrderLines($expand=MasterStockRecord)";
// But EF wants it like this: "SalesOrderLines.MasterStockRecord";
expandProperties[expandIndex] = expandProperties[expandIndex].Replace(" ", "");
expandProperties[expandIndex] = expandProperties[expandIndex].Replace("($expand=", ".");
expandProperties[expandIndex] = expandProperties[expandIndex].Replace(")", "");
}
var selectProperties = source.SelectExpand == null || string.IsNullOrWhiteSpace(source.SelectExpand.RawSelect) ? new List<string>().ToArray() : source.SelectExpand.RawSelect.Split(',');
//Now do the same for Select (incomplete)
var propertiesToExpand = expandProperties.Union(selectProperties).ToArray();
return propertiesToExpand;
}
这对于扩展很有效，所以现在我可以处理以下请求：
/odatademo/SalesOrders('123456')?$expand=SalesOrderLines
或者更复杂的请求，如：
/odatademo/SalesOrders('123456')?$expand=SalesOrderLines($expand=MasterStockRecord)
但是，试图将 $select 与 $expand 结合的更复杂的请求将失败：
/odatademo/SalesOrders('123456')?$expand=SalesOrderLines($select=OrderQuantity)
Sequence contains no elements
所以，问题是：我是否正确地处理了这个问题？ 我觉得必须编写一些代码来解析和转换 ODataQueryOptions，使它们能够被 EF 理解，这让人感到非常不舒服。
似乎这是一个相当流行的话题：
- odata-expand-dtos-and-entity-framework
- how-to-specify-the-shape-of-results-with-webapi2-odata-with-expand
- web-api-queryable-how-to-apply-automapper
- how-do-i-map-an-odata-query-against-a-dto-to-another-entity
尽管大多数建议使用 ProjectTo，但似乎没有一个解决序列化自动扩展属性或如何处理扩展的方法，如果已配置 ExplictExpansion。
以下是类和配置：
Entity Framework (V6.1.3) 实体：
public class SalesOrderHeader
{
public string SalesOrderNumber { get; set; }
public string Alpha { get; set; }
public string Customer { get; set; }
public string Status { get; set; }
public virtual ICollection<SalesOrderLine> SalesOrderLines { get; set; }
}
public class SalesOrderLine
{
public string SalesOrderNumber { get; set; }
public string OrderLineNumber { get; set; }
public string Product { get; set; }
public string Description { get; set; }
public decimal OrderQuantity { get; set; }
public virtual SalesOrderHeader SalesOrderHeader { get; set; }
public virtual MasterStockRecord MasterStockRecord { get; set; }
}
public class MasterStockRecord
{
public string ProductCode { get; set; }
public string Description { get; set; }
public decimal Quantity { get; set; }
}
OData（V6.13.0）数据传输对象：
public class SalesOrderDto
{
[Key]
public string SalesOrderNumber { get; set; }
public string Customer { get; set; }
public string Status { get; set; }
public virtual ICollection<SalesOrderLineDto> SalesOrderLines { get; set; }
}
public class SalesOrderLineDto
{
[Key]
[ForeignKey("SalesOrderHeader")]
public string SalesOrderNumber { get; set; }
[Key]
public string OrderLineNumber { get; set; }
public string LineType { get; set; }
public string Product { get; set; }
public string Description { get; set; }
public decimal OrderQuantity { get; set; }
public virtual SalesOrderDto SalesOrderHeader { get; set; }
public virtual StockDto MasterStockRecord { get; set; }
}
public class StockDto
{
[Key]
public string StockCode { get; set; }
public string Description { get; set; }
public decimal Quantity { get; set; }
}
OData 配置：
var builder = new ODataConventionModelBuilder();
builder.EntitySet<StockDto>("Stock");
builder.EntitySet<SalesOrderDto>("SalesOrders");
builder.EntitySet<SalesOrderLineDto>("SalesOrderLines");