[英]Dynamic Lambda expressions for filter and sorting using children using c#
您好,我按照https://docs.microsoft.com/zh-CN/dotnet/csharp/programming-guide/concepts/expression-trees/how-to-use-expression-trees-to-build-dynamic-查询以在我的关系类中创建过滤器和排序,我需要使用子列“ Channel”进行过滤和排序
这是我的基础课
public class MeterTransaction : EviModelBase
{
public int TariffDuration { get; set; }
public decimal? TariffPackageKwh { get; set; }
public decimal? TariffPackagePrice { get; set; }
public decimal? TariffRatePerKwh { get; set; }
public decimal? TariffRateMinFee { get; set; }
// Meter CreditBalance after transaction
public decimal CreditBalance { get; set; }
public DateTimeOffset? CreditExpiration { get; set; }
[Timestamp]
public byte[] RowVersion { get; set; }
public Meter Meter { get; set; }
}
这是仪表类
public class Meter : EviModelBase
{
public MeterVendor Vendor { get; set; }
public string Model { get; set; }
public string SerialNumber { get; set; }
public string Channel { get; set; }
}
这是用于过滤和排序数据的代码:
public static IQueryable<T> OrderByNew<T>(this IQueryable<T> source, SortModel sortModel)
{
ParameterExpression p = Expression.Parameter(typeof(T), "p");
// Construct the nested properties
string[] nestedProps = sortModel.ColId.Split('.');
Expression mbr = p;
for (int i = 0; i < nestedProps.Length; i++)
mbr = Expression.PropertyOrField(mbr, nestedProps[i]);
LambdaExpression pred = Expression.Lambda(
Expression.Equal(
mbr,
Expression.Constant("EVI0000101")
),
p
);
var method = string.Equals(sortModel.Sort, "desc", StringComparison.OrdinalIgnoreCase) ?
"OrderByDescending" :
"OrderBy";
var whereCallExpression = Expression.Call(typeof(Queryable), "where", new Type[] { source.ElementType }, source.Expression, pred);
var orderByExpression = Expression.Lambda(mbr, p);
MethodCallExpression orderByCallExpression = Expression.Call(
typeof(Queryable),
method,
new Type[] { source.ElementType},
whereCallExpression,
Expression.Quote(orderByExpression));
// ***** End OrderBy *****
return source.Provider.CreateQuery<T>(orderByCallExpression);
}
}
实际上,“ whereCallExpression”正在工作,并过滤了我想要的数据而没有错误,但是排序逻辑给出了一个错误“类型'System.Linq.Queryable'上没有通用方法'OrderBy'与提供的类型实参和实参兼容“。
我怎样才能做到这一点?
问候
您缺少这样一个事实,与Where
, OrderBy
方法具有2个泛型类型参数( TSource
和TKey
)。 因此,在生成呼叫时,您需要同时提供它们:
var orderByCallExpression = Expression.Call(
typeof(Queryable),
method,
new Type[] { source.ElementType, orderByExpression.Body.Type }, // <--
whereCallExpression,
Expression.Quote(orderByExpression));
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