如何在一个generics扩展方法中使用string列名在IQueryable上应用OrderBy？
public static IQueryable<TResult> ApplySortFilter<T, TResult>(this IQueryable<T> query, string columnName) where T : EntityObject { var param = Expression.Parameter(typeof(T), "o"); var body = Expression.PropertyOrField(param,columnName); var sortExpression = Expression.Lambda(body, param); return query.OrderBy(sortExpression); } 因为OrderBy的types不是从sortExpression推断的，我需要在运行时指定它：
var sortExpression = Expression.Lambda<T, TSortColumn>(body, param);
要么
return query.OrderBy<T, TSortColumn>(sortExpression);
我不认为这是可能的，但是TSortColumn只能在运行时确定。
有没有解决的办法？
我们在LINQ to SQL项目中做了类似的事情（不是100％相同，但相似）。 代码如下：
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string ordering, params object[] values) { var type = typeof(T); var property = type.GetProperty(ordering); var parameter = Expression.Parameter(type, "p"); var propertyAccess = Expression.MakeMemberAccess(parameter, property); var orderByExp = Expression.Lambda(propertyAccess, parameter); MethodCallExpression resultExp = Expression.Call(typeof(Queryable), "OrderBy", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp)); return source.Provider.CreateQuery<T>(resultExp); }
我们实际上并没有使用通用的，我们有一个已知的类，但它应该工作在一个generics（我已经把通用的占位符应该在哪里）。
编辑：对于降序，请传递OrderByDescending而不是“OrderBy”：
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), "OrderByDescending", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
你也可以使用Dynamic Linq
C＃在这里下载http://msdn.microsoft.com/en-us/vcsharp/bb894665.aspx
然后只需添加使用Linq.Dynamic; 并自动获得2个额外的扩展方法，可以这样使用
return query.OrderBy("StringColumnName");
我已经扩展你的函数来添加对子属性的支持。
private static LambdaExpression GenerateSelector<TEntity>(String propertyName, out Type resultType) where TEntity : class { // Create a parameter to pass into the Lambda expression (Entity => Entity.OrderByField). var parameter = Expression.Parameter(typeof(TEntity), "Entity"); // create the selector part, but support child properties PropertyInfo property; Expression propertyAccess; if (propertyName.Contains('.')) { // support to be sorted on child fields. String[] childProperties = propertyName.Split('.'); property = typeof(TEntity).GetProperty(childProperties[0]); propertyAccess = Expression.MakeMemberAccess(parameter, property); for (int i = 1; i < childProperties.Length; i++) { property = property.PropertyType.GetProperty(childProperties[i]); propertyAccess = Expression.MakeMemberAccess(propertyAccess, property); } } else { property = typeof(TEntity).GetProperty(propertyName); propertyAccess = Expression.MakeMemberAccess(parameter, property); } resultType = property.PropertyType; // Create the order by expression. return Expression.Lambda(propertyAccess, parameter); } private static MethodCallExpression GenerateMethodCall<TEntity>(IQueryable<TEntity> source, string methodName, String fieldName) where TEntity : class { Type type = typeof(TEntity); Type selectorResultType; LambdaExpression selector = GenerateSelector<TEntity>(fieldName, out selectorResultType); MethodCallExpression resultExp = Expression.Call(typeof(Queryable), methodName, new Type[] { type, selectorResultType }, source.Expression, Expression.Quote(selector)); return resultExp; }
您可以使用这些function，如：
GenerateMethodCall<TEntity>(source, "OrderByDescending", fieldName);
我用你的想法为OrderBy的扩展方法。 但是在“多对多”的情况下，我得到了错误。 例如，你有表网站，客户和Customer_site。 对于给定的网站，我想sorting客户名称和OrderBy扩展（当我通过“site.customer”，其中customer是导航属性）我得到错误行：propertyAccess = Expression.MakeMemberAccess（propertyAccess，property）;
这是我使用的（有一些增强:-)）：
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByValues) where TEntity : class { IQueryable<TEntity> returnValue = null; string orderPair = orderByValues.Trim().Split(',')[0]; string command = orderPair.ToUpper().Contains("DESC") ? "OrderByDescending" : "OrderBy"; var type = typeof(TEntity); var parameter = Expression.Parameter(type, "p"); string propertyName = (orderPair.Split(' ')[0]).Trim(); System.Reflection.PropertyInfo property; MemberExpression propertyAccess; if (propertyName.Contains('.')) { // support to be sorted on child fields. String[] childProperties = propertyName.Split('.'); property = typeof(TEntity).GetProperty(childProperties[0]); propertyAccess = Expression.MakeMemberAccess(parameter, property); for (int i = 1; i < childProperties.Length; i++) { Type t = property.PropertyType; if (!t.IsGenericType) { property = t.GetProperty(childProperties[i]); } else { property = t.GetGenericArguments().First().GetProperty(childProperties[i]); } propertyAccess = Expression.MakeMemberAccess(propertyAccess, property); } } else { property = type.GetProperty(propertyName); propertyAccess = Expression.MakeMemberAccess(parameter, property); } var orderByExpression = Expression.Lambda(propertyAccess, parameter); var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExpression)); returnValue = source.Provider.CreateQuery<TEntity>(resultExpression); if (orderByValues.Trim().Split(',').Count() > 1) { // remove first item string newSearchForWords = orderByValues.ToString().Remove(0, orderByValues.ToString().IndexOf(',') + 1); return source.OrderBy(newSearchForWords); } return returnValue; }
问候
斯洛博丹
看来， 这是做到这一点的方法，现在来validation：
// ***** OrderBy(company => company) ***** // Create an expression tree that represents the expression // 'whereCallExpression.OrderBy(company => company)' MethodCallExpression orderByCallExpression = Expression.Call( typeof(Queryable), "OrderBy", new Type[] { queryableData.ElementType, queryableData.ElementType }, whereCallExpression, Expression.Lambda<Func<string, string>>(pe, new ParameterExpression[] { pe })); // ***** End OrderBy *****
如果你可以添加“System.Linq.Dynamic”包，那么太容易没有任何复杂的，
从NuGet软件包pipe理器中获取“System.Linq.Dynamic”软件包，然后按照您的需要进行操作，
例如：
public IQueryable<TEntity> GetWithInclude(Expression<Func<TEntity, bool>> predicate, List<string> sortBy, int pageNo, int pageSize = 12, params string[] include) { try { var numberOfRecordsToSkip = pageNo * pageSize; var dynamic = DbSet.AsQueryable(); foreach (var s in include) { dynamic.Include(s); } return dynamic.OrderBy("CreatedDate").Skip(numberOfRecordsToSkip).Take(pageSize); } catch (Exception e) { throw new Exception(e.Message); } }
希望这会有所帮助
我修复了这个代码： https : //stackoverflow.com/a/1670085/5852630
此代码适用于顺序sorting：首先执行“OrderBy”，然后执行“ThenBy”（不是“OrderBy”！）
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByValues) where TEntity : class { IQueryable<TEntity> returnValue = null; string[] orderPairs = orderByValues.Trim().Split(','); Expression resultExpression = source.Expression; string strAsc = "OrderBy"; string strDesc = "OrderByDescending"; foreach (string orderPair in orderPairs) { if (string.IsNullOrWhiteSpace(orderPair)) continue; string[] orderPairArr = orderPair.Trim().Split(' '); string propertyName = orderPairArr[0].Trim(); string orderNarrow = orderPairArr.Length > 1 ? orderPairArr[1].Trim() : string.Empty; string command = orderNarrow.ToUpper().Contains("DESC") ? strDesc : strAsc; Type type = typeof(TEntity); ParameterExpression parameter = Expression.Parameter(type, "p"); System.Reflection.PropertyInfo property; Expression propertyAccess; if (propertyName.Contains('.')) { // support to be sorted on child fields. String[] childProperties = propertyName.Split('.'); property = typeof(TEntity).GetProperty(childProperties[0]); propertyAccess = Expression.MakeMemberAccess(parameter, property); for (int i = 1; i < childProperties.Length; i++) { Type t = property.PropertyType; if (!t.IsGenericType) { property = t.GetProperty(childProperties[i]); } else { property = t.GetGenericArguments().First().GetProperty(childProperties[i]); } propertyAccess = Expression.MakeMemberAccess(propertyAccess, property); } } else { property = type.GetProperty(propertyName); propertyAccess = Expression.MakeMemberAccess(parameter, property); } if (property.PropertyType == typeof(object)) { propertyAccess = Expression.Call(propertyAccess, "ToString", null); } LambdaExpression orderByExpression = Expression.Lambda(propertyAccess, parameter); resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType == typeof(object) ? typeof(string) : property.PropertyType }, resultExpression, Expression.Quote(orderByExpression)); strAsc = "ThenBy"; strDesc = "ThenByDescending"; } returnValue = source.Provider.CreateQuery<TEntity>(resultExpression); return returnValue; }
