如何使用我作为参数的值指定传递给orderby的参数？
例如：
List<Student> existingStudends = new List<Student>{ new Student {...}, new Student {...}}
目前正在实施：
List<Student> orderbyAddress = existingStudends.OrderBy(c => c.Address).ToList();
而不是c.Address，我如何将其作为参数？
示例
string param = "City";
List<Student> orderbyAddress = existingStudends.OrderByDescending(c => param).ToList();
答案 0 :(得分：114)
这是使用反射的可能性......
var param = "Address";
var propertyInfo = typeof(Student).GetProperty(param);
var orderByAddress = items.OrderBy(x => propertyInfo.GetValue(x, null));
答案 1 :(得分：100)
您可以使用一点反射来构造表达式树，如下所示（这是一种扩展方法）：
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty,
bool desc)
{
string command = desc ? "OrderByDescending" : "OrderBy";
var type = typeof(TEntity);
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, "p");
var 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));
return source.Provider.CreateQuery<TEntity>(resultExpression);
}
orderByProperty是您要订购的属性名称，如果将desc作为参数传递，则将按降序排序;否则，将按升序排序。
现在您应该能够existingStudents.OrderBy("City",true);或existingStudents.OrderBy("City",false);
答案 2 :(得分：6)
2）添加以下代码
public static class OrderUtils
{
public static string ToStringForOrdering<T, TKey>(this Expression<Func<T, TKey>> expression, bool isDesc = false)
{
var str = expression.Body.ToString();
var param = expression.Parameters.First().Name;
str = str.Replace("Convert(", "(").Replace(param + ".", "");
return str + (isDesc ? " descending" : "");
}
}
3）写下您的开关以选择Lambda函数
public static class SortHelper
{
public static Expression<Func<UserApp, object>> UserApp(string orderProperty)
{
orderProperty = orderProperty?.ToLowerInvariant();
switch (orderProperty)
{
case "firstname":
return x => x.PersonalInfo.FirstName;
case "lastname":
return x => x.PersonalInfo.LastName;
case "fullname":
return x => x.PersonalInfo.FirstName + x.PersonalInfo.LastName;
case "email":
return x => x.Email;
}
}
}
4）使用你的助手
Dbset.OrderBy(SortHelper.UserApp("firstname").ToStringForOrdering())
5）你可以使用pagging（PagedList）
public virtual IPagedList<T> GetPage<TOrder>(Page page, Expression<Func<T, bool>> where, Expression<Func<T, TOrder>> order, bool isDesc = false,
params Expression<Func<T, object>>[] includes)
{
var orderedQueryable = Dbset.OrderBy(order.ToStringForOrdering(isDesc));
var query = orderedQueryable.Where(where).GetPage(page);
query = AppendIncludes(query, includes);
var results = query.ToList();
var total = Dbset.Count(where);
return new StaticPagedList<T>(results, page.PageNumber, page.PageSize, total);
}
<强>解释
System.Linq.Dynamic允许我们在OrderBy方法中设置字符串值。但是在这个扩展中，字符串将被解析为Lambda。所以我认为如果我们将Lambda解析为字符串并将其提供给OrderBy方法将会有效。它有效！
答案 3 :(得分：5)
private Func<T, object> GetOrderByExpression<T>(string sortColumn)
{
Func<T, object> orderByExpr = null;
if (!String.IsNullOrEmpty(sortColumn))
{
Type sponsorResultType = typeof(T);
if (sponsorResultType.GetProperties().Any(prop => prop.Name == sortColumn))
{
System.Reflection.PropertyInfo pinfo = sponsorResultType.GetProperty(sortColumn);
orderByExpr = (data => pinfo.GetValue(data, null));
}
}
return orderByExpr;
}
public List<T> OrderByDir<T>(IEnumerable<T> source, string dir, Func<T, object> OrderByColumn)
{
return dir.ToUpper() == "ASC" ? source.OrderBy(OrderByColumn).ToList() : source.OrderByDescending(OrderByColumn).ToList();``
}
// Call the code like below
var orderByExpression= GetOrderByExpression<SearchResultsType>(sort);
var data = OrderByDir<SponsorSearchResults>(resultRecords, SortDirectionString, orderByExpression);
答案 4 :(得分：4)
这是我提出的处理条件Descending的事情。您可以将此与其他动态生成keySelector func的方法结合使用。
public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source,
System.Linq.Expressions.Expression<Func<TSource, TKey>> keySelector,
System.ComponentModel.ListSortDirection sortOrder
)
{
if (sortOrder == System.ComponentModel.ListSortDirection.Ascending)
return source.OrderBy(keySelector);
else
return source.OrderByDescending(keySelector);
}
用法：
//imagine this is some parameter
var direction = System.ComponentModel.ListSortDirection.Ascending;
query = query.OrderBy(ec => ec.MyColumnName, direction);
请注意，这允许您将此.OrderBy扩展名与新参数链接到任何IQueryable上。
// perhaps passed in as a request of user to change sort order
// var direction = System.ComponentModel.ListSortDirection.Ascending;
query = context.Orders
.Where(o => o.Status == OrderStatus.Paid)
.OrderBy(ec => ec.OrderPaidUtc, direction);
答案 5 :(得分：3)
要扩展answer by @Icarus：如果您希望扩展方法的返回类型是IOrderedQueryable而不是IQueryable，您只需按如下方式转换结果：
public static IOrderedQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty, bool desc)
{
string command = desc ? "OrderByDescending" : "OrderBy";
var type = typeof(TEntity);
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, "p");
var 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));
return (IOrderedQueryable<TEntity>)source.Provider.CreateQuery<TEntity>(resultExpression);
}
答案 6 :(得分：2)
这不允许您传递string，正如您在问题中所要求的那样，但它可能仍适合您。
OrderByDescending方法需要Func<TSource, TKey>，因此您可以这样重写函数：
List<Student> QueryStudents<TKey>(Func<Student, TKey> orderBy)
{
return existingStudents.OrderByDescending(orderBy).ToList();
}
OrderByDescending还有其他重载需要Expression<Func<TSource, TKey>>和/或IComparer<TKey>。您还可以查看这些内容并查看它们是否为您提供了任何使用方法。
答案 7 :(得分：1)
唯一对我有用的解决方案是由neoGeneva发布在https://gist.github.com/neoGeneva/1878868。
我会重新发布他的代码，因为它运作良好，我不希望它丢失在互联网中！
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortExpression)
{
if (source == null)
throw new ArgumentNullException("source", "source is null.");
if (string.IsNullOrEmpty(sortExpression))
throw new ArgumentException("sortExpression is null or empty.", "sortExpression");
var parts = sortExpression.Split(' ');
var isDescending = false;
var propertyName = "";
var tType = typeof(T);
if (parts.Length > 0 && parts[0] != "")
{
propertyName = parts[0];
if (parts.Length > 1)
{
isDescending = parts[1].ToLower().Contains("esc");
}
PropertyInfo prop = tType.GetProperty(propertyName);
if (prop == null)
{
throw new ArgumentException(string.Format("No property '{0}' on type '{1}'", propertyName, tType.Name));
}
var funcType = typeof(Func<,>)
.MakeGenericType(tType, prop.PropertyType);
var lambdaBuilder = typeof(Expression)
.GetMethods()
.First(x => x.Name == "Lambda" && x.ContainsGenericParameters && x.GetParameters().Length == 2)
.MakeGenericMethod(funcType);
var parameter = Expression.Parameter(tType);
var propExpress = Expression.Property(parameter, prop);
var sortLambda = lambdaBuilder
.Invoke(null, new object[] { propExpress, new ParameterExpression[] { parameter } });
var sorter = typeof(Queryable)
.GetMethods()
.FirstOrDefault(x => x.Name == (isDescending ? "OrderByDescending" : "OrderBy") && x.GetParameters().Length == 2)
.MakeGenericMethod(new[] { tType, prop.PropertyType });
return (IQueryable<T>)sorter
.Invoke(null, new object[] { source, sortLambda });
}
return source;
}
答案 8 :(得分：1)
要扩展@Icarus的响应：如果要按两个字段排序，我可以执行以下功能（对于一个字段，Icarius的响应效果很好）。
public static IQueryable<T> OrderByDynamic<T>(this IQueryable<T> q, string SortField1, string SortField2, bool Ascending)
{
var param = Expression.Parameter(typeof(T), "p");
var body = GetBodyExp(SortField1, SortField2, param);
var exp = Expression.Lambda(body, param);
string method = Ascending ? "OrderBy" : "OrderByDescending";
Type[] types = new Type[] { q.ElementType, exp.Body.Type };
var mce = Expression.Call(typeof(Queryable), method, types, q.Expression, exp);
return q.Provider.CreateQuery<T>(mce);
}
这是主体为lambda表达式返回的函数，它可以与string和int一起使用，但是足以添加更多类型以使其根据每个程序员的需要工作
public static NewExpression GetBodyExp(string field1, string field2, ParameterExpression Parametro)
{
// SE OBTIENE LOS NOMBRES DE LOS TIPOS DE VARIABLE
string TypeName1 = Expression.Property(Parametro, field1).Type.Name;
string TypeName2 = Expression.Property(Parametro, field2).Type.Name;
// SE DECLARA EL TIPO ANONIMO SEGUN LOS TIPOS DE VARIABLES
Type TypeAnonymous = null;
if (TypeName1 == "String")
{
string var1 = "0";
if (TypeName2 == "Int32")
{
int var2 = 0;
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
if (TypeName2 == "String")
{
string var2 = "0";
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
}
if (TypeName1 == "Int32")
{
int var1 = 0;
if (TypeName2 == "Int32")
{
string var2 = "0";
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
if (TypeName2 == "String")
{
string var2 = "0";
var example = new { var1, var2 };
TypeAnonymous = example.GetType();
}
}
//se declaran los TIPOS NECESARIOS PARA GENERAR EL BODY DE LA EXPRESION LAMBDA
MemberExpression[] args = new[] { Expression.PropertyOrField(Parametro, field1), Expression.PropertyOrField(Parametro, field2) };
ConstructorInfo CInfo = TypeAnonymous.GetConstructors()[0];
IEnumerable<MemberInfo> a = TypeAnonymous.GetMembers().Where(m => m.MemberType == MemberTypes.Property);
//BODY
NewExpression body = Expression.New(CInfo, args, TypeAnonymous.GetMembers().Where(m => m.MemberType == MemberTypes.Property));
return body;
}
要使用它，请完成以下操作
IQueryable<MyClass> IqMyClass= context.MyClass.AsQueryable();
List<MyClass> ListMyClass= IqMyClass.OrderByDynamic("UserName", "IdMyClass", true).ToList();
如果有更好的方法可以做到这一点，那么如果他们共享它就很好了
由于How can I make a Multiple property lambda expression with Linq
，我设法解决了该问题答案 9 :(得分：0)
我迟到了，但这些解决方案都不适合我。我很想尝试System.Linq.Dynamic，但我在Nuget上找不到，可能会折旧？无论哪种方式......
这是我提出的解决方案。我需要动态使用 OrderBy ， OrderByDescending 和 OrderBy＆gt;的混合物。 ThenBy
我只是为我的列表对象创建了一个扩展方法，我知道有点hacky ...我不推荐这个，如果它是我做了很多的东西，但它对一个人来说很好。
List<Employee> Employees = GetAllEmployees();
foreach(Employee oEmployee in Employees.ApplyDynamicSort(eEmployeeSort))
{
//do stuff
}
public static IOrderedEnumerable<Employee> ApplyDynamicSort(this List<Employee> lEmployees, Enums.EmployeeSort eEmployeeSort)
{
switch (eEmployeeSort)
{
case Enums.EmployeeSort.Name_ASC:
return lEmployees.OrderBy(x => x.Name);
case Enums.EmployeeSort.Name_DESC:
return lEmployees.OrderByDescending(x => x.Name);
case Enums.EmployeeSort.Department_ASC_Salary_DESC:
return lEmployees.OrderBy(x => x.Department).ThenByDescending(y => y.Salary);
default:
return lEmployees.OrderBy(x => x.Name);
}
}
答案 10 :(得分：0)
将nugget包 Dynamite 添加到您的代码中
添加名称空间 Dynamite.Extensions 例如：使用Dynamite.Extensions;
按查询命令，就像任何SQL查询一样 例如：students.OrderBy（“城市DESC，地址”）。ToList（）;
答案 11 :(得分：0)
新答案：这是一个更完整的答案，它支持多个列，例如 SQL。示例：.OrderBy("FirstName,Age DESC")：
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string orderByProperty, bool desc, bool isThenBy = false)
{
string command = isThenBy ? (desc ? "ThenByDescending" : "ThenBy") : (desc ? "OrderByDescending" : "OrderBy");
var type = typeof(TEntity);
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, "p");
var 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));
return source.Provider.CreateQuery<TEntity>(resultExpression);
}
public static IQueryable<TEntity> OrderBy<TEntity>(this IQueryable<TEntity> source, string sqlOrderByList)
{
var ordebyItems = sqlOrderByList.Trim().Split(',');
IQueryable<TEntity> result = source;
bool useThenBy = false;
foreach (var item in ordebyItems)
{
var splt = item.Trim().Split(' ');
result = result.OrderBy(splt[0].Trim(), (splt.Length > 1 && splt[1].Trim().ToLower() == "desc"), useThenBy);
if (useThenBy)
useThenBy = true;
}
return result;
}
第二个函数遍历 orderby 列并使用第一个。