本例简化了此代码。
查询实际上是从服务返回的,这就是为什么我更喜欢用这种方式编写方法。
[HttpGet]
public PageResult<ExceptionLog> Logging(ODataQueryOptions<ExceptionLog> options)
{
var query = from o in _exceptionLoggingService.entities.ExceptionDatas
select new ExceptionLog {
ExceptionDataId = o.ExceptionDataId,
SiteId = o.SiteId,
ExceptionDateTime = o.ExceptionDateTime,
StatusCode = o.StatusCode,
Url = o.Url,
ExceptionType = o.ExceptionType,
ExceptionMessage = o.ExceptionMessage,
Exception = o.Exception,
RequestData = o.RequestData
};
var results = options.ApplyTo(query) as IEnumerable<ExceptionLog>;
var count = results.LongCount();
return new PageResult<ExceptionLog>(results, Request.GetNextPageLink(), count);
}
上面的代码在"results.LongCount()"上出现错误,并出现以下异常:
SqlException: The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.
我在尝试分页时似乎遇到了一个异常,比如"$top=2"。如果我的查询字符串是这样的"$filter=ExceptionDataId gt 100",一切都很好。
由于ExceptionData(实体)与ExceptionLog(业务模型)匹配,我可以做一些类似的工作:
[HttpGet]
public PageResult<ExceptionLog> Logging(ODataQueryOptions<ExceptionData> options)
{
var query = from o in _exceptionLoggingService.entities.ExceptionDatas
orderby o.ExceptionDateTime descending
select o;
var results = from o in options.ApplyTo(query) as IEnumerable<ExceptionData>
select new ExceptionLog {
ExceptionDataId = o.ExceptionDataId,
SiteId = o.SiteId,
ExceptionDateTime = o.ExceptionDateTime,
StatusCode = o.StatusCode,
Url = o.Url,
ExceptionType = o.ExceptionType,
ExceptionMessage = o.ExceptionMessage,
Exception = o.Exception,
RequestData = o.RequestData
};
return new PageResult<ExceptionLog>(results, Request.GetNextPageLink(), results.LongCount());
}
但这对我来说并不完全有效,因为它有点烦人,而且我不能使用该服务的方法,因为它已经给了我一个IQueryable。
另一件需要注意的事情是,如果将Logging方法转换为IQueryable,则一切正常。但是我需要用查询返回Count,所以我必须返回一个PageResult。
这是我正在使用的解决方法。我只应用ODataQueryOptions中的筛选器,并手动应用Top和Skip。
首先我创建了一些扩展方法:
using System;
using System.Collections.Generic;
using System.Linq;
namespace System.Web.Http.OData.Query
{
public static class ODataQuerySettingsExtensions
{
public static IEnumerable<T> ApplyFilter<T>(this IQueryable<T> query, ODataQueryOptions<T> options)
{
if (options.Filter == null)
{
return query;
}
return options.Filter.ApplyTo(query, new ODataQuerySettings()) as IEnumerable<T>;
}
public static IEnumerable<T> ApplyTopAndTake<T>(this IEnumerable<T> query, ODataQueryOptions<T> options)
{
IEnumerable<T> value = query;
if (options.Top != null)
{
value = value.Take(options.Top.Value);
}
if (options.Skip != null)
{
value = value.Skip(options.Skip.Value);
}
return value;
}
}
}
现在我的方法是这样的:
[HttpGet]
public PageResult<ExceptionLog> Logging(ODataQueryOptions<ExceptionLog> options)
{
// GetLogs returns an IQueryable<ExceptionLog> as seen in Question above.
var query = _exceptionLoggingService.GetLogs()
.ApplyFilter(options);
var count = query.Count();
var results = query.ApplyTopAndTake(options);
return new PageResult<ExceptionLog>(results, Request.GetNextPageLink(), count);
}