如何在通用扩展方法中使用字符串列名在IQueryable上应用OrderBy？

我们在LINQ to SQL项目中做了类似的事情(不是100%相同,但相似).这是代码:

public static IQueryable OrderBy(this IQueryable 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(resultExp);
}

我们实际上并没有使用泛型,我们有一个已知的类,但它应该在泛型上工作(我把通用占位符放在它应该的位置).

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));

这工作得很好,但以下只是一个非常好的干净代码示例:http://stackoverflow.com/questions/41244/dynamic-linq-orderby (3认同)

参数`values`是什么？ (2认同)

---

Jeremy Coene.. 29

您也可以使用Dynamic Linq

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

C#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个可以像这样使用的额外扩展方法

return query.OrderBy("StringColumnName");

---

Davy Landman.. 12

我扩展了您的功能以添加对Child Properties的支持.

private static LambdaExpression GenerateSelector(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(IQueryable source, string methodName, String fieldName) where TEntity : class
{
    Type type = typeof(TEntity);
    Type selectorResultType;
    LambdaExpression selector = GenerateSelector(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(source, "OrderByDescending", fieldName);

---

小智.. 8

我将你的想法用于OrderBy的扩展方法.但是在"多对多"的情况下,我会收到错误.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扩展名进行排序(当我传递"site.customer",其中客户是导航属性时)我得到错误:propertyAccess = Expression.MakeMemberAccess(propertyAccess,property);

这是我使用的(有一些增强功能:-)):

public static IQueryable OrderBy(this IQueryable source, string orderByValues) where TEntity : class
{
  IQueryable 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(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

1> Aaron Powell..：

---

我们在LINQ to SQL项目中做了类似的事情(不是100%相同,但相似).这是代码:

public static IQueryable OrderBy(this IQueryable 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(resultExp);
}

我们实际上并没有使用泛型,我们有一个已知的类,但它应该在泛型上工作(我把通用占位符放在它应该的位置).

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));

---

这工作得很好,但以下只是一个非常好的干净代码示例:http://stackoverflow.com/questions/41244/dynamic-linq-orderby

---

参数`values`是什么？

2> Jeremy Coene..：

---

您也可以使用Dynamic Linq

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

C#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个可以像这样使用的额外扩展方法

return query.OrderBy("StringColumnName");

3> Davy Landman..：

---

我扩展了您的功能以添加对Child Properties的支持.

private static LambdaExpression GenerateSelector(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(IQueryable source, string methodName, String fieldName) where TEntity : class
{
    Type type = typeof(TEntity);
    Type selectorResultType;
    LambdaExpression selector = GenerateSelector(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(source, "OrderByDescending", fieldName);

4> 小智..：

---

我将你的想法用于OrderBy的扩展方法.但是在"多对多"的情况下,我会收到错误.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扩展名进行排序(当我传递"site.customer",其中客户是导航属性时)我得到错误:propertyAccess = Expression.MakeMemberAccess(propertyAccess,property);

这是我使用的(有一些增强功能:-)):

public static IQueryable OrderBy(this IQueryable source, string orderByValues) where TEntity : class
{
  IQueryable 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(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

5> JTew..：

---

看来这是做到这一点的方法,现在来验证:

// ***** 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>(pe, new ParameterExpression[] { pe }));
// ***** End OrderBy *****