将 DTO 与 OData 和 Web API 结合使用

Question

使用 Web API 和 OData，我有一个公开数据传输对象而不是 Entity Framework 实体的服务。

我使用 AutoMapper 使用 ProjectTo():

将 EF 实体转换为其 DTO 计数器部分

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) 配置如下，注意 ExplicitExpansion() 防止序列化自动扩展导航属性，当它们没有被请求时：

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() 然后会产生一个新问题，其中以下请求会引发错误：

/odatademo/SalesOrders('123456')?$expand=SalesOrderLines

The query specified in the URI is not valid. The specified type member 'SalesOrderLines' is not supported in LINQ to Entities

导航属性 SalesOrderLines 对 EF 来说是未知的，所以这个错误几乎是我预期会发生的。问题是，我该如何处理这种类型的请求？

ProjectTo() 方法确实有一个重载，允许我传入一个需要扩展的属性数组，我发现并修改了扩展方法 ToNavigationPropertyArray 以尝试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;
}

这适用于扩展，所以现在我可以处理如下请求：

/odatademo/SalesOrders('123456')?$expand=SalesOrderLines

或更复杂的请求，例如：

/odatademo/SalesOrders('123456')?$expand=SalesOrderLines($expand=MasterStockRecord)

但是，尝试将 $select 与 $expand 组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：我的处理方式是否正确？感觉很臭，我必须写一些东西来解析并将 ODataQueryOptions 转换成 EF 可以理解的东西。

看来这个话题比较热门：

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

虽然其中大部分建议使用 ProjectTo，但 none 似乎解决了序列化自动扩展属性的问题，或者如果已配置 ExplictExpansion 则如何处理扩展的问题。

类和配置如下：

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");

Answer 1

我从来没有真正设法解决这个问题。 ToNavigationPropertyArray() 扩展方法有一点帮助，但不能处理无限深度导航。

真正的解决方案是创建 Actions 或 Functions 以允许客户端请求需要更复杂查询的数据。

另一种方法是进行多次 smaller/simple 调用，然后在客户端上聚合数据，但这并不理想。

Answer 2

当您想在 AutoMapper 中标记某些内容以进行显式扩展时，您还需要在调用 ProjectTo<>() 时选择重新加入。

// map
cfg.CreateMap<SalesOrderHeader, SalesOrderDto>()                
   .ForMember(dest => dest.SalesOrderLines, opt => opt.ExplicitExpansion());

// updated controller
[EnableQuery]
public IQueryable<SalesOrderDto> Get()
{
    return _dbContext.SalesOrders
        .ProjectTo<SalesOrderDto>(
            AutoMapperConfig.Config, 
            so => so.SalesOrderLines,
            // ... additional opt-ins
        );
}

虽然 AutoMapper wiki 确实说明了这一点，但该示例可能有点误导，因为它不包括成对的 ExplicitExpansion() 调用。

To control which members are expanded during projection, set ExplicitExpansion in the configuration and then pass in the members you want to explicitly expand:

Answer 3

我已经创建了一个 Automapper 显式导航扩展实用函数，它应该与 N-deph 扩展一起使用。将它张贴在这里，因为它可能会对某人有所帮助。

public List<string> ProcessExpands(IEnumerable<SelectItem> items, string parentNavPath="")
{
    var expandedPropsList = new List<String>();
    if (items == null) return expandedPropsList;

    foreach (var selectItem in items)
    {
        if (selectItem is ExpandedNavigationSelectItem)
        {
            var expandItem = selectItem as ExpandedNavigationSelectItem;
            var navProperty = expandItem.PathToNavigationProperty?.FirstSegment?.Identifier;

            expandedPropsList.Add($"{parentNavPath}{navProperty}");                    
            //go recursively to subproperties
            var subExpandList = ProcessExpands(expandItem?.SelectAndExpand?.SelectedItems, $"{parentNavPath}{navProperty}.");
            expandedPropsList =  expandedPropsList.Concat(subExpandList).ToList();
        }
    }
    return expandedPropsList;
}

你可以调用它:

var navExp = ProcessExpands(options?.SelectExpand?.SelectExpandClause?.SelectedItems)

它将return一个包含["Parent" ,"Parent.Child"]

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将 DTO 与 OData 和 Web API 结合使用

Using DTO's with OData & Web API

asp.net

entity-framework

automapper

odata

asp.net-web-api