如何使用通用扩展方法中的字符串列名在 IQueryable 上应用 OrderBy?

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【中文标题】如何使用通用扩展方法中的字符串列名在 IQueryable 上应用 OrderBy?【英文标题】:How do I apply OrderBy on an IQueryable using a string column name within a generic extension method? 【发布时间】:2010-09-23 09:05:19 【问题描述】:
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 的类型不是从 sortExpression 推断出来的,所以我需要在运行时指定类似这样的内容:

var sortExpression = Expression.Lambda<T, TSortColumn>(body, param);

或者

return query.OrderBy<T, TSortColumn>(sortExpression);

但我认为这是不可能的,因为 TSortColumn 只能在运行时确定。

有没有办法解决这个问题?

【问题讨论】:

不确定this 是否您在寻找什么,但请看一下。干杯 @JTew 我如何按子句实现第二个订单..say orderby id then by date 【参考方案1】:

我们在 LINQ to SQL 项目中做了类似的事情(不是 100% 相同,而是类似)。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泛型,我们有一个已知的类,但它应该适用于泛型(我已将泛型占位符放在它应该在的位置)。

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));

【讨论】:

嘿,没有问题,我不能给自己分配答案:) 对于降序,传入 "OrderByDescending" 而不是 "OrderBy" MethodCallExpression resultExp = Expression.Call(typeof(Queryable), "OrderByDescending", ... 这工作得很好,但以下只是一个非常好的干净代码示例:***.com/questions/41244/dynamic-linq-orderby 参数values是干什么用的? 未使用值【参考方案2】:

您也可以使用动态 Linq

信息在这里 http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

C# 在这里下载 http://msdn.microsoft.com/en-us/vcsharp/bb894665.aspx

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");

【讨论】:

谢谢,我在 Phil Haack 网站的样本中看到过 Linq.Dynamic,但不确定。周末我会玩这个。 Systems.Linq.Dynamic.dll 可以从这里下载:github.com/kahanu/System.Linq.Dynamic【参考方案3】:

我已经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;

您可以使用以下功能:

GenerateMethodCall<TEntity>(source, "OrderByDescending", fieldName);

【讨论】:

你是我的英雄!! 要爱聪明的人 我尝试了这段代码,它确实适用于一个孩子,但不能适用于多个孩子,例如它适用于对 x.String 和 x.Object.String 进行排序,但不适用于对 x.Object.Object.String 进行排序。【参考方案4】:

我将您的想法用于 OrderBy 的扩展方法。但在“多对多”的情况下,我会出错。例如,您有表 Site、Customer 和 Customer_site。 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”时,客户是导航属性)我在行中遇到错误:propertyAccess = Expression.MakeMemberAccess(propertyAccess, property);

这是我使用的(带有一些增强功能:-)):

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

【讨论】:

【参考方案5】:

似乎this 是这样做的方法,现在验证一下:

// ***** 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 *****

【讨论】:

妈的,落后了 34 秒! :P【参考方案6】:

如果您能够添加“System.Linq.Dynamic”包,那么, 太简单了,没有任何复杂性,

然后从 NuGet 包管理器中获取 insatll 包“System.Linq.Dynamic” 根据您的需要尝试如下,

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

【讨论】:

【参考方案7】:

我稍微修正了这段代码:https://***.com/a/1670085/5852630

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;

【讨论】:

【参考方案8】:

这是我对@Davy Landman的回答(我想要一个扩展方法)的改编,我做了一点简化。

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);
    

可以这样使用:

gridview1.DataSource = DbContext.TB_CARS.SortBy("model", SortDirection.Descending);
//OR
gridview1.DataSource = DbContext.TB_CARS.SortBy("owner.first_name", 0);

【讨论】:

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