如果您对c#–DynamicFunc,IOrderedQueryable>Expression感兴趣，那么本文将是一篇不错的选择，我们将为您详在本文中，您将会了解到关于c#–DynamicFunc,I
如果您对c# – Dynamic Func,IOrderedQueryable> Expression感兴趣，那么本文将是一篇不错的选择，我们将为您详在本文中，您将会了解到关于c# – Dynamic Func,IOrderedQueryable> Expression的详细内容，并且为您提供关于"One or more types required to compile a dynamic expression cannot be found. Are you missing...、AS 报错 Program type already present: permissions.dispatcher.GrantableRequest、c# – System.Linq.Expressions.Expression for .OrderBy函数、c# – 如何从Property Name创建Expression> expression的有价值信息。
本文目录一览：- c# – Dynamic Func,IOrderedQueryable> Expression
- "One or more types required to compile a dynamic expression cannot be found. Are you missing...
- AS 报错 Program type already present: permissions.dispatcher.GrantableRequest
- c# – System.Linq.Expressions.Expression for .OrderBy函数
- c# – 如何从Property Name创建Expression> expression
c# – Dynamic Func,IOrderedQueryable> Expression
我正在使用这里提到的模式
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application
我正在使用下面的方法来查询EF
public virtual IEnumerable<TEntity> Get(
Expression<Func<TEntity,bool>> filter = null,Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>> orderBy = null,string includeProperties = "")
{
IQueryable<TEntity> query = dbSet;
if (filter != null)
{
query = query.Where(filter);
}
foreach (var includeProperty in includeProperties.Split
(new char[] { ',' },StringSplitOptions.RemoveEmptyEntries))
{
query = query.Include(includeProperty);
}
if (orderBy != null)
{
return orderBy(query).ToList();
}
else
{
return query.ToList();
}
}
现在我想创建动态Func< IQueryable< TEntity>,IOrderedQueryable< TEntity>>表达式来订购我的数据.
我只知道字段名称为字符串和顺序类型(升序,降序)为字符串(asc,desc)
解决方法
最后我可以写出我想要的方法.
public static Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>> GetorderBy(string orderColumn,string orderType) {
Type typeQueryable = typeof(IQueryable<TEntity>);
ParameterExpression argQueryable = Expression.Parameter(typeQueryable,"p");
var outerExpression = Expression.Lambda(argQueryable,argQueryable);
string[] props = orderColumn.Split('.');
IQueryable<TEntity> query = new List<TEntity>().AsQueryable<TEntity>();
Type type = typeof(TEntity);
ParameterExpression arg = Expression.Parameter(type,"x");
Expression expr = arg;
foreach(string prop in props) {
PropertyInfo pi = type.GetProperty(prop,BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
expr = Expression.Property(expr,pi);
type = pi.PropertyType;
}
LambdaExpression lambda = Expression.Lambda(expr,arg);
string methodName = orderType == "asc" ? "OrderBy" : "OrderByDescending";
MethodCallExpression resultExp =
Expression.Call(typeof(Queryable),methodName,new Type[] { typeof(TEntity),type },outerExpression.Body,Expression.Quote(lambda));
var finalLambda = Expression.Lambda(resultExp,argQueryable);
return (Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>>)finalLambda.Compile();
}
此方法有两个参数,第一个是字段名,另一个是asc或desc.
方法的结果可以直接与IQueryable对象一起使用.
谢谢你的帮助
"One or more types required to compile a dynamic expression cannot be found. Are you missing...
#事故现场：
在一个.net 4.0 的项目中使用 dynamic，示例代码如下：
1 private static void Main(string[] args)
2 {
3 dynamic obj;
4 obj = new { name = "jack" };
5 Console.WriteLine(obj.name);
6 }在读取 obj.name 时，报错：
One or more types required to compile a dynamic expression cannot be found. Are you missing references to Microsoft.CSharp.dll and System.Core.dll?
#解决方法：
在项目中，添加 Microsoft.CSharp.dll 的引用；
#参考：
https://stackoverflow.com/questions/11725514/one-or-more-types-required-to-compile-a-dynamic-expression-cannot-be-found-are
——————————————————————————————————————————————————
AS 报错 Program type already present: permissions.dispatcher.GrantableRequest
Program type already present: permissions.dispatcher.GrantableRequest
报错，无法打包
c# – System.Linq.Expressions.Expression for .OrderBy函数
我的代码的行部分是重复的.
您将看到下面的lambda表达式重复4次
x => x.GetValue<string>("City")).ThenByDescending(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"),x.GetValue<string[]>("EventTimeZone")[0].ToString())
代码示例：
//SORT DATA
switch (SortDetails)
{
case ("Date"):
default:
if (SortOrder == "ASC")
{
_allEvents = _allEvents.OrderBy(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"),x.GetValue<string[]>("EventTimeZone")[0].ToString()));
}
else
{
_allEvents = _allEvents.OrderByDescending(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"),x.GetValue<string[]>("EventTimeZone")[0].ToString()));
}
break;
case ("Location"):
if (SortOrder == "ASC")
{
_allEvents = _allEvents.OrderBy(x => x.GetValue<string>("Country")).ThenBy(x => x.GetValue<string>("ProvinceState")).ThenBy(x => x.GetValue<string>("City")).ThenBy(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"),x.GetValue<string[]>("EventTimeZone")[0].ToString()));
}
else
{
_allEvents = _allEvents.OrderByDescending(x => x.GetValue<string>("Country")).ThenByDescending(x => x.GetValue<string>("ProvinceState")).ThenByDescending(x => x.GetValue<string>("City")).ThenByDescending(x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"),x.GetValue<string[]>("EventTimeZone")[0].ToString()));
}
break;
}
我想采取第一行,并使其成为我可以进入OrderBy的东西.
就像是 ：
System.Linq.Expressions.Expression<Func<DynamicContent,DateTime>> sortLambda = x => HelperFunctions.strToTZDateTime(x.GetValue<string>("EventStartStr"),x.GetValue<string[]>("EventTimeZone")[0].ToString());
进入：
allEvents = _allEvents.OrderBy(sortLambda);
不幸的是,这似乎并没有奏效.
解决方法
这个控制台应用程序应该修复你. sortLamda可以是任何类型,希望能回答有关动态内容的问题.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
internal class BoringEvent
{
public string EventStartStr { get; set; }
public string EventTimeZone { get; set; }
public string ProvinceState { get; set; }
public string City { get; set; }
public string Country { get; set; }
}
internal enum SortedBy
{
Ascending = 0,Descending
}
class ExpressionsTest
{
internal static List<BoringEvent> _allEvents = new List<BoringEvent>();
internal static class HelperFunctions
{
public static DateTime strToTZDateTime(string startDate,string timeZone)
{
//I'm too lazy to figure out dates by time zone.
//Your function already has the logic,so why bother.
//Let's assume the time zone is equal in this test case
return DateTime.Parse(startDate);
}
}
internal static void Main()
{
_allEvents.Add(new BoringEvent {
EventStartStr = "12/31/1999",//let's party like it's 1999 - (yawn) I'm stuck at this event :<
EventTimeZone = "en-us",City = "Philadelphia",ProvinceState = "Pennsylvania",Country = "United States of America"});
_allEvents.Add(new BoringEvent
{
EventStartStr = "01/01/1970",EventTimeZone = "en-us",City = "New York",ProvinceState = "New York",Country = "United States of America"
});
IEnumerable<BoringEvent> sortedEvents = null;
//sort by date
Console.WriteLine("Sorting Events by Ascending date...");
Expression<Func<BoringEvent,DateTime>> sortLamba = evt => HelperFunctions.strToTZDateTime(evt.EventStartStr,evt.EventTimeZone);
sortedEvents = _allEvents.sortEvents(SortedBy.Ascending,sortLamba);
Print(sortedEvents);
//sort by country,then state,then city,then date
Console.WriteLine("Sorting Events Desc by Country,then ProvinceState,then City,then Date");
Expression<Func<BoringEvent,object>>[] sortLamba2 = new Expression<Func<BoringEvent,object>>[]
{
evt => evt.Country,evt => evt.ProvinceState,evt => evt.City,evt => HelperFunctions.strToTZDateTime(evt.EventStartStr,evt.EventTimeZone)
};
sortedEvents = _allEvents.sortEvents(SortedBy.Descending,sortLamba2);
Print(sortedEvents);
Console.Read();
}
private static void Print(IEnumerable<BoringEvent> events)
{
for(int i = 0; i < events.Count(); i++)
{
BoringEvent evt = events.ElementAt(i);
Console.WriteLine("Event: {0}",i.ToString());
Console.WriteLine("\tEventStartStr: {0}",evt.EventStartStr);
Console.WriteLine("\tEventTimeZone: {0}",evt.EventTimeZone);
Console.WriteLine("\tCity: {0}",evt.City);
Console.WriteLine("\tProvinceState: {0}",evt.ProvinceState);
Console.WriteLine("\tCountry: {0}",evt.Country);
}
}
}
internal static class EventExtensions
{
public static IEnumerable<TResult> SortEvents<TResult,T>(
this IEnumerable<TResult> events,SortedBy sortByType,params Expression<Func<TResult,T>>[] expressions)
{
IEnumerable<TResult> retVal = null;
switch(sortByType)
{
case SortedBy.Ascending:
retVal = EventExtensions.sortEventsAsc(events,expressions);
break;
case SortedBy.Descending:
retVal = EventExtensions.sortEventsDesc(events,expressions);
break;
default:
throw new InvalidOperationException(
string.Format("The SortedBy enumeration does not contain a case for the value of '{0}'.",Enum.GetName(typeof(SortedBy),sortByType)));
}
return retVal;
}
public static IEnumerable<TResult> SortEventsAsc<TResult,T>>[] expressions)
{
IOrderedEnumerable<TResult> sorted = null;
for(int i = 0; i < expressions.Count(); i++)
{
Expression<Func<TResult,T>> exp =
(Expression<Func<TResult,T>>)expressions[i];
Func<TResult,T> deleg = exp.Compile();
if(i == 0)
{
sorted = events.OrderBy(evt => deleg.Invoke(evt));
}
else
{
sorted = sorted.ThenBy(evt => deleg.Invoke(evt));
}
}
return sorted;
}
public static IEnumerable<TResult> SortEventsDesc<TResult,T>>[] expressions)
{
IOrderedEnumerable<TResult> sorted = null;
for (int i = 0; i < expressions.Count(); i++)
{
Expression<Func<TResult,T> deleg = exp.Compile();
if (i == 0)
{
sorted = events.OrderByDescending(evt => deleg.Invoke(evt));
}
else
{
sorted = sorted.ThenByDescending(evt => deleg.Invoke(evt));
}
}
return sorted;
}
}
c# – 如何从Property Name创建Expression> expression
我的
Html帮助方法如下所示
public static MvcHtmlString Control<TModel>(this MyHtmlHelper<TModel> helper,string propertyName,LayoutHelper layout,TemplateType templateType = TemplateType.Screen)
{
//...
}
我想将我的属性名称转换为以下内容
Expression<Func<TModel,string>> expression
任何帮助都感激不尽
解决方法
看起来你想要调用ModelMetadata.FromLambdaExpression,而不是FromStringExpression.你可以创建一个表达式
x => x.PropertyName
从头开始,像这样：
// Get a reference to the property var propertyInfo = ExpressionHelper.GetPropertyInfo<TModel>(propertyName); var model = ExpressionHelper.Parameter<TModel>(); // Build the LINQ expression tree backwards: // x.Prop var key = ExpressionHelper.GetPropertyExpression(model,propertyInfo); // x => x.Prop var keySelector = ExpressionHelper.GetLambda(typeof(TModel),propertyInfo.PropertyType,model,key);
为了使代码更具可读性,将细节表达式树操作移入此辅助类：
public static class ExpressionHelper
{
private static readonly MethodInfo Lambdamethod = typeof(Expression)
.getmethods()
.First(x => x.Name == "Lambda" && x.ContainsGenericParameters && x.GetParameters().Length == 2);
private static MethodInfo GetLambdaFuncBuilder(Type source,Type dest)
{
var predicateType = typeof(Func<,>).MakeGenericType(source,dest);
return Lambdamethod.MakeGenericmethod(predicateType);
}
public static PropertyInfo GetPropertyInfo<T>(string name)
=> typeof(T).GetProperties()
.Single(p => p.Name == name);
public static ParameterExpression Parameter<T>()
=> Expression.Parameter(typeof(T));
public static MemberExpression GetPropertyExpression(ParameterExpression obj,PropertyInfo property)
=> Expression.Property(obj,property);
public static LambdaExpression GetLambda<TSource,TDest>(ParameterExpression obj,Expression arg)
=> GetLambda(typeof(TSource),typeof(TDest),obj,arg);
public static LambdaExpression GetLambda(Type source,Type dest,ParameterExpression obj,Expression arg)
{
var lambdaBuilder = GetLambdaFuncBuilder(source,dest);
return (LambdaExpression)lambdaBuilder.Invoke(null,new object[] { arg,new[] { obj } });
}
}
从头开始构建表达式树使您在创建lambda表达式时具有最大的灵活性.根据目标属性类型,它可能不总是表达式< Func< TModel,string>> – 最后一种类型可以是int或其他类型.无论目标属性类型如何,此代码都将构建正确的表达式树.
今天关于c# – Dynamic Func,IOrderedQueryable> Expression的讲解已经结束，谢谢您的阅读，如果想了解更多关于"One or more types required to compile a dynamic expression cannot be found. Are you missing...、AS 报错 Program type already present: permissions.dispatcher.GrantableRequest、c# – System.Linq.Expressions.Expression for .OrderBy函数、c# – 如何从Property Name创建Expression> expression的相关知识，请在本站搜索。
本文标签：
