LINQ中的多个"order by"

Question

我有两个表,movies并且categories,我首先按类别ID获取有序列表,然后按名称获取.

影片表有三列,ID,Name和CategoryID.类别表2包含列,ID和名称.

我尝试了类似下面的内容,但它没有用.

var movies = _db.Movies.OrderBy( m => { m.CategoryID, m.Name })

Answer 1

这应该适合你:

var movies = _db.Movies.OrderBy(c => c.Category).ThenBy(n => n.Name)

Answer 2

使用非lambda查询语法LINQ,您可以这样做:

var movies = from row in _db.Movies 
             orderby row.Category, row.Name
             select row;

[EDIT来解决评论]要控制排序顺序,请使用关键字ascending(这是默认值,因此不是特别有用),或者descending像这样:

var movies = from row in _db.Movies 
             orderby row.Category descending, row.Name
             select row;

Answer 3

添新":

var movies = _db.Movies.OrderBy( m => new { m.CategoryID, m.Name })

这适用于我的盒子.它确实返回了可用于排序的东西.它返回一个具有两个值的对象.

类似但不同于按组合列排序,如下所示.

var movies = _db.Movies.OrderBy( m => (m.CategoryID.ToString() + m.Name))

Answer 4

使用DataContext上的以下行将DataContext上的SQL活动记录到控制台 - 然后您可以确切地看到您的linq语句从数据库请求的内容:

_db.Log = Console.Out

以下LINQ语句:

var movies = from row in _db.Movies 
             orderby row.CategoryID, row.Name
             select row;

和

var movies = _db.Movies.OrderBy(m => m.CategoryID).ThenBy(m => m.Name);

产生以下SQL:

SELECT [t0].ID, [t0].[Name], [t0].CategoryID
FROM [dbo].[Movies] as [t0]
ORDER BY [t0].CategoryID, [t0].[Name]

然而,在Linq中重复OrderBy似乎会反转生成的SQL输出:

var movies = from row in _db.Movies 
             orderby row.CategoryID
             orderby row.Name
             select row;

和

var movies = _db.Movies.OrderBy(m => m.CategoryID).OrderBy(m => m.Name);

产生以下SQL(Name和CategoryId被切换):

SELECT [t0].ID, [t0].[Name], [t0].CategoryID
FROM [dbo].[Movies] as [t0]
ORDER BY [t0].[Name], [t0].CategoryID

Answer 5

我已经创建了一些扩展方法(如下所示),因此您不必担心是否已经订购了IQueryable.如果您想按多个属性订购,请按以下步骤操作:

// We do not have to care if the queryable is already sorted or not. 
// The order of the Smart* calls defines the order priority
queryable.SmartOrderBy(i => i.Property1).SmartOrderByDescending(i => i.Property2);

如果您从要排序的属性列表中动态创建排序,这将特别有用.

public static class IQueryableExtension
{
    public static bool IsOrdered<T>(this IQueryable<T> queryable) {
        if(queryable == null) {
            throw new ArgumentNullException("queryable");
        }

        return queryable.Expression.Type == typeof(IOrderedQueryable<T>);
    }

    public static IQueryable<T> SmartOrderBy<T, TKey>(this IQueryable<T> queryable, Expression<Func<T, TKey>> keySelector) {
        if(queryable.IsOrdered()) {
            var orderedQuery = queryable as IOrderedQueryable<T>;
            return orderedQuery.ThenBy(keySelector);
        } else {
            return queryable.OrderBy(keySelector);
        }
    }

    public static IQueryable<T> SmartOrderByDescending<T, TKey>(this IQueryable<T> queryable, Expression<Func<T, TKey>> keySelector) {
        if(queryable.IsOrdered()) {
            var orderedQuery = queryable as IOrderedQueryable<T>;
            return orderedQuery.ThenByDescending(keySelector);
        } else {
            return queryable.OrderByDescending(keySelector);
        }
    }
}

Answer 6

使用LINQ至少还有一种方法可以做到这一点,尽管不是最简单的方法.您可以使用使用的OrberBy()方法来完成IComparer.首先,你需要IComparer为这样的Movie类实现一个:

public class MovieComparer : IComparer<Movie>
{
    public int Compare(Movie x, Movie y)
    {
        if (x.CategoryId == y.CategoryId)
        {
            return x.Name.CompareTo(y.Name);
        }
        else
        {
            return x.CategoryId.CompareTo(y.CategoryId);
        }
    }
}

然后您可以使用以下语法订购电影:

var movies = _db.Movies.OrderBy(item => item, new MovieComparer());

如果您需要将其中一个项目的顺序切换为降序,只需在相应的Compare() 方法内切换x和y即可MovieComparer.

Answer 7

如果使用通用存储库

> lstModule = _ModuleRepository.GetAll().OrderBy(x => new { x.Level,
> x.Rank}).ToList();

别的

> _db.Module.Where(x=> ......).OrderBy(x => new { x.Level, x.Rank}).ToList();