c# - ASP.NET Web Api OData v4 - 如何通过 $metadata 反射(reflect)小数位数和精度？

Question

使用 ASP.NET Web API 2.2/OData v4.0 是否可以在 $metadata 端点中定义小数位数和精度？

目前我已经定义了一个包含许多小数属性的 PricingModel.cs:

...
public decimal? PurchasePrice { get; set; }        
public decimal? SellingPrice { get; set; }
...

PricingController.cs继承自ODataController，并在Startup.cs中定义了一个基本的实体数据模型:

public void Configuration(IAppBuilder appBuilder)
{
    var config = new HttpConfiguration();

    // Model builder
    ODataModelBuilder builder = new ODataConventionModelBuilder();
    builder.EntitySet<PricingModel>("Pricing");

    // Map route (Default)
    config.MapODataServiceRoute(
        routeName: "ODataRoute",
        routePrefix: null,
        model: builder.GetEdmModel());

    appBuilder.UseWebApi(config);
}

$metadata 中反射(reflect)的是(缺少比例和精度):

...    
<Property Name="PurchasePrice" Type="Edm.Decimal"/>
<Property Name="SellingPrice" Type="Edm.Decimal"/>
...

OData Version 4.0 Common Schema Definition应该允许将比例和精度包含在 $metadata 中。

6.2.4 Attribute Scale

A decimal property MAY define a non-negative integer value or variable for the Scale attribute.

This attribute specifies the maximum number of digits allowed to the right of the decimal point.

The value variable means that the number of digits to the right of the decimal point may vary from zero to the value of the Precision attribute.

An integer value means that the number of digits to the right of the decimal point may vary from zero to the value of the Scale attribute, and the number of digits to the left of the decimal point may vary from one to the value of the Precision attribute minus the value of the Scale attribute. If Precision is equal to Scale, a single zero has to precede the decimal point.

The value of the Scale attribute MUST be less than or equal to the value of the Precision attribute. If no value is specified, the Scale facet defaults to zero.

Note: if the underlying data store allows negative scale, services may use a Precision attribute with the absolute value of the negative scale added to the actual number of significant decimal digits, and client-provided values may have to be rounded before being stored.

Example 9: Precision and Scale facets applied to the Decimal type. Allowed values: 1.23, 0.23, 3.14 and 0.7, not allowed values: 123, 12.3.

<Property Name="Amount" Type="Edm.Decimal" Precision="3" Scale="2" />

Example 10: Precision equals Scale. Allowed values: 0.23, 0,7, not allowed values: 1.23, 1.2.

<Property Name="Amount" Type="Edm.Decimal" Precision="2" Scale="2" />

Example 11: Precision and a variable Scale applied to the Decimal type. Allowed values: 0.123, 1.23, 0.23, 0.7, 123 and 12.3, not allowed would be: 12.34, 1234 and 123.4 due to the limited precision.

<Property Name="Amount" Type="Edm.Decimal" Precision="3" Scale="variable" />

阅读Configure the OData Endpoint我知道我可能应该通过 ODataModelBuilder 实例以某种方式修改实体数据模型 (EDM)，但似乎找不到解决方法。

An EDM is an abstract model of the data. The EDM is used to create the service metadata document. The ODataConventionModelBuilder class creates an EDM by using default naming conventions. This approach requires the least code. If you want more control over the EDM, you can use the ODataModelBuilder class to create the EDM by adding properties, keys, and navigation properties explicitly.

Answer 1

下面的代码成功了，也许对其他人有帮助......

...
// Model builder
ODataModelBuilder builder = new ODataConventionModelBuilder();
builder.EntitySet<PricingModel>("Pricing");
builder.EntitySet<PricingModel>("Pricing").EntityType.Property(x => x.PurchasePrice).Precision = 19;
builder.EntitySet<PricingModel>("Pricing").EntityType.Property(x => x.PurchasePrice).Scale = 3;
...

这就是现在 $metadata 中反射(reflect)的内容...

...
<Property Name="PurchasePrice" Type="Edm.Decimal" Precision="19" Scale="3"/>
...