動態按lambda表達式排序

我在我的應用程序中進行排序，如下所示。動態按lambda表達式排序

public IQueryable<Users> SelectAll(string sSortExpression, string sSortOrder) 
{ 
    if (sSortOrder == "asc") 
    { 
     switch (sSortExpression) 
     { 
      case "FirstName": 
       return UsersRepository.Entities.OrderBy(x => x.FirstName); 
      case "LastName": 
       return UsersRepository.Entities.OrderBy(x => x.LastName); 
      default: 
       return UsersRepository.Entities.OrderBy(x => x.Id); 
     } 
    } 
    else 
    { 
     switch (sSortExpression) 
     { 
      case "FirstName": 
       return UsersRepository.Entities.OrderByDescending(x => x.FirstName); 
      case "LastName": 
       return UsersRepository.Entities.OrderByDescending(x => x.LastName); 
      default: 
       return UsersRepository.Entities.OrderByDescending(x => x.UserName); 
     } 
    } 
}

現在它的罰款，但我必須到所有領域中Users表（大約30場）排序。然後，該方法將是非常大的

我嘗試使用反射像這樣

public IQueryable<Users> SelectAll(string sSortExpression, string sSortOrder) 
{ 
    var _property = UsersRepository.GetType().GetProperties().Where(a => a.Name == sSortExpression); 
    if (sSortOrder == "asc") 
    { 
     return UsersRepository.Entities.OrderBy(x => _property); 
    } 
    else 
    { 
     return UsersRepository.Entities.OrderByDescending(x => _property); 
    } 
}

但zhcon失敗。

有沒有更好的方法來做到這一點？在此先感謝

來源

2014-02-06 Fool

最簡單的方法去：改變你的方法接受Expression而不是string：

public IQueryable<Users> SelectAll<TProp>(Expression<Func<Users, TProp>> selector, string sSortOrder) 
{ 
    if (sSortOrder == "asc") 
    { 
     return UsersRepository.Entities.OrderBy(selector); 
    } 
    else 
    { 
     return UsersRepository.Entities.OrderByDescending(selector); 
    } 
}

你可以稱它爲爲：

SelectAll(x => x.LastName, "asc");

或者，如果你真的需要它的字符串，你必須使用System.Linq.Expressions.Expression類方法來生成表達式樹：

public IQueryable<Users> SelectAll<TProp>(string sSortExpression, string sSortOrder) 
{ 
    var param = Expression.Parameter(typeof(Users)); 
    var propExpression = Expression.Lambda<Func<Users, TProp>>(Expression.Property(param, sSortExpression), param); 

    if (sSortOrder == "asc") 
    { 
     return UsersRepository.Entities.OrderBy(propExpression); 
    } 
    else 
    { 
     return UsersRepository.Entities.OrderByDescending(propExpression); 
    } 
}

不過這需要對SelectAll調用指定的泛型類型參數：

var results = SelectAll<int>("Id", "asc");

來源

2014-02-06 05:47:43 MarcinJuraszek

TProp：找不到類型命名空間 – Fool

您是否更改了方法聲明以包含''通用參數？ – MarcinJuraszek

它現在工作正常。謝謝 – Fool

您可以創建你的表達進行排序像

public IQueryable<Users> SelectAllByCompany(string sSortExpression, string sSortOrder) 
{ 
    var p = Expression.Parameter(typeof(Users),"u"); 
    var sortExpr = Expression.Lambda<Func<User,object>>(Expresion.Property(p,sSortExpression), p); 

    if (sSortOrder == "asc") 
    { 
     return UsersRepository.Entities.OrderBy(sortExpr); 
    } 
    else 
    { 
     return UsersRepository.Entities.OrderByDescending(sortExpr); 
    } 
}

來源

2014-02-06 05:45:50 Grundy

使用這種擴展方法： 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); }

然後使用Users.OrderBy（sSortExpression，真要是降下來，如果上升FALSE）

來源

2016-09-21 08:09:26

動態按lambda表達式排序

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