C# 如何在通用扩展方法中使用字符串列名在 IQueryable 上应用 OrderBy？
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How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
提问by JTew
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);
}
Because the type for OrderBy is not inferred from sortExpression I need to specify it something like this at run time:
因为 OrderBy 的类型不是从 sortExpression 推断出来的，所以我需要在运行时指定它像这样：
var sortExpression = Expression.Lambda<T, TSortColumn>(body, param);
Or
或者
return query.OrderBy<T, TSortColumn>(sortExpression);
I don't think this is possible however as TSortColumn can only be determined during runtime.
我认为这是不可能的，因为 TSortColumn 只能在运行时确定。
Is there a way around this?
有没有解决的办法？
采纳答案by Aaron Powell
We did something similar (not 100% the same, but similar) in a LINQ to SQL project. Here's the code:
我们在 LINQ to SQL 项目中做了类似的事情（不是 100% 相同，而是相似）。这是代码：
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);
}
We didn't actually use a generic, we had a known class, but it should work on a generic (I've put the generic placeholder where it should be).
我们实际上并没有使用泛型，我们有一个已知的类，但它应该适用于泛型（我已经将泛型占位符放在了它应该在的地方）。
Edit:For descending order, pass in OrderByDescendinginstead of "OrderBy":
编辑：对于降序，传入OrderByDescending而不是“OrderBy”：
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), "OrderByDescending", new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp));
回答by JTew
It seems that thisis the way to do it, now to verify that:
似乎这是这样做的方法，现在来验证一下：
// ***** 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 *****
回答by Davy Landman
I've extended your functions to add support for Child Properties.
我扩展了您的功能以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;
}
You can use these functions like:
您可以使用这些功能，例如：
GenerateMethodCall<TEntity>(source, "OrderByDescending", fieldName);
回答by Jeremy Coenen
You can also use Dynamic Linq
您还可以使用动态 Linq
C# download here http://msdn.microsoft.com/en-us/vcsharp/bb894665.aspx
C# 在这里下载 http://msdn.microsoft.com/en-us/vcsharp/bb894665.aspx
Then just add the using Linq.Dynamic; and you automatically get 2 additional extension methods that can be used like this
然后只需添加 using Linq.Dynamic; 你会自动获得 2 个额外的扩展方法，可以像这样使用
return query.OrderBy("StringColumnName");
回答by Slobodan
I used your idea for extension method for OrderBy. But in case of "many to many" I am getting error. For example you have table Site, Customer and Customer_site. For given Site I want to sort by customer name and in OrderBy extension (when I pass "site.customer" where customer is navigation property) I get error in line: propertyAccess = Expression.MakeMemberAccess(propertyAccess, property);
我将您的想法用于 OrderBy 的扩展方法。但是在“多对多”的情况下，我会出错。例如，您有 Site、Customer 和 Customer_site 表。对于给定的站点，我想按客户名称和 OrderBy 扩展名排序（当我传递“site.customer”，其中客户是导航属性时）我在行中收到错误：propertyAccess = Expression.MakeMemberAccess(propertyAccess, property);
This is what I use (with some enhancements :-) ):
这就是我使用的（有一些改进:-)）：
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;
}
Regards
问候
Slobodan
斯洛博丹
回答by dush88c
If you are able to add "System.Linq.Dynamic" package then, Too easy without any complication,
如果您能够添加“System.Linq.Dynamic”包，那么简单而没有任何复杂性，
fisrt insatll package "System.Linq.Dynamic" from NuGet package manager then try as below as your need,
来自 NuGet 包管理器的 fisrt insatll 包“System.Linq.Dynamic”，然后根据需要尝试如下操作，
Ex:
前任：
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);
}
}
Hope this will help
希望这会有所帮助
回答by SeroJah
I fixed this code a bit: https://stackoverflow.com/a/1670085/5852630
我修复了这个代码：https: //stackoverflow.com/a/1670085/5852630
This code works with sequential sorting: first execute "OrderBy", then "ThenBy"(Not "OrderBy"!)
此代码适用于顺序排序：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;
}
回答by M Granja
Here is my adaptation from @Davy Landman's answer (I wanted an extension method) and I simplified a bit.
这是我对@Davy Landman的回答的改编（我想要一个扩展方法），我做了一些简化。
public static IQueryable<T> SortBy<T>(this IQueryable<T> source,
String propertyName,
WebControls.SortDirection direction)
{
if (source == null) throw new ArgumentNullException("source");
if (String.IsNullOrEmpty(propertyName)) return source;
// Create a parameter to pass into the Lambda expression
//(Entity => Entity.OrderByField).
var parameter = Expression.Parameter(typeof(T), "Entity");
// create the selector part, but support child properties (it works without . too)
String[] childProperties = propertyName.Split('.');
MemberExpression property = Expression.Property(parameter, childProperties[0]);
for (int i = 1; i < childProperties.Length; i++)
{
property = Expression.Property(property, childProperties[i]);
}
LambdaExpression selector = Expression.Lambda(property, parameter);
string methodName = (direction > 0) ? "OrderByDescending" : "OrderBy";
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), methodName,
new Type[] { source.ElementType, property.Type },
source.Expression, Expression.Quote(selector));
return source.Provider.CreateQuery<T>(resultExp);
}
It can be used like this:
它可以像这样使用：
gridview1.DataSource = DbContext.TB_CARS.SortBy("model", SortDirection.Descending);
//OR
gridview1.DataSource = DbContext.TB_CARS.SortBy("owner.first_name", 0);
