没有通用方法“ThenBy"

I am trying to add the ThenById() method which will be launched after a call to OrderBy() on IOrderedQueryable:public static IOrderedQueryable<TEntity> ThenById<TEntity>(this IQueryable<TEntity> source){ if (source == null) { throw new ArgumentNullException(nameof(source)); } var command = "ThenBy"; var thenByProperty = "Id"; var type = typeof(TEntity); if (type.GetProperty(thenByProperty) == null) { throw new MissingFieldException(nameof(thenByProperty)); } var param = Expression.Parameter(type, "p"); var property = type.GetProperty(thenByProperty, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance); var propertyAccess = Expression.MakeMemberAccess(param, property); var orderByExpression = Expression.Lambda(propertyAccess, param); var resultExpression = Expression.Call( typeof(IOrderedQueryable), command, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExpression)); return (IOrderedQueryable<TEntity>)source.Provider.CreateQuery<TEntity>(resultExpression);}我收到以下错误消息:System.Linq.IOrderedQueryable"类型上的任何泛型方法ThenBy"都与提供的类型参数和参数不兼容.如果方法是非泛型的，则不应提供类型参数. No generic method 'ThenBy' on type 'System.Linq.IOrderedQueryable' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic.推荐答案ThenBy 扩展方法在 System.Linq.Queryable 类中，不在 中IOrderedQueryable.你只需要在你的代码中替换它:The ThenBy extension method is in the System.Linq.Queryable class, not in IOrderedQueryable. You simply need to replace that in your code:public static IOrderedQueryable<TEntity> ThenById<TEntity>( this IOrderedQueryable<TEntity> source){ //snip var resultExpression = Expression.Call( typeof(System.Linq.Queryable), command, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExpression)); return (IOrderedQueryable<TEntity>)source.Provider.CreateQuery<TEntity>(resultExpression);}请注意，该方法应该扩展 IOrderedQueryable，而不仅仅是 IQueryable.Note that the method should be extending IOrderedQueryable, not just IQueryable.但是，如果 TEntity 没有 Id 属性，这将在运行时失败.我的偏好是为所有具有 Id 属性的实体提供一个接口，并在此处使用通用约束.这样你就可以完全避免表达式并获得编译时安全.例如:However, this will fail at runtime if TEntity doesn't have an Id property. My preference would be to give all entities with the Id property an interface and use a generic constraint here. That way you avoid expressions completely and get compile time safety. For example:public interface IHasId{ int Id { get; set; }}public class SomeEntity : IHasId{ public int Id { get; set; } public string Name { get; set; } //etc}这简化了您的扩展方法:Which simplifies your extension method:public static IOrderedQueryable<TEntity> ThenById<TEntity>( this IOrderedQueryable<TEntity> source) where TEntity : IHasId{ return source.ThenBy(e => e.Id);} 这篇关于没有通用方法“ThenBy"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！