从Linq到Sql的随机行

#1 楼

partial class MyDataContext {
     [Function(Name="NEWID", IsComposable=true)] 
     public Guid Random() 
     { // to prove not used by our C# code... 
         throw new NotImplementedException(); 
     }
}

var cust = (from row in ctx.Customers
           where row.IsActive // your filter
           orderby ctx.Random()
           select row).FirstOrDefault();

var qry = from row in ctx.Customers
          where row.IsActive
          select row;

int count = qry.Count(); // 1st round-trip
int index = new Random().Next(count);

Customer cust = qry.Skip(index).FirstOrDefault(); // 2nd round-trip

#2 楼

var customers = db.Customers
                  .Where(c => c.IsActive)
                  .OrderBy(c => Guid.NewGuid())
                  .FirstOrDefault();

#3 楼

public static T RandomElement<T>(this IEnumerable<T> source,
                                 Random rng)
{
    T current = default(T);
    int count = 0;
    foreach (T element in source)
    {
        count++;
        if (rng.Next(count) == 0)
        {
            current = element;
        }            
    }
    if (count == 0)
    {
        throw new InvalidOperationException("Sequence was empty");
    }
    return current;
}

#4 楼

Random random = new Random();
int seed = random.Next();
result = result.OrderBy(s => (~(s.Shuffle & seed)) & (s.Shuffle | seed)); // ^ seed);

#5 楼

var rows = Table.OrderBy(t => Guid.NewGuid())
                        .Take(count);

#6 楼

#7 楼

List<string> lst = new List<string>();
lst.Add("Apple"); 
lst.Add("Guva");
lst.Add("Graps"); 
lst.Add("PineApple");
lst.Add("Orange"); 
lst.Add("Mango");

var customers = lst.OrderBy(c => Guid.NewGuid()).FirstOrDefault();

#8 楼

Dim Aleatorio As New Random()

Dim Paginas = From a As SPListItem In Sitio.RootWeb.Lists("Páginas") Order By Aleatorio.Next Take 3

#9 楼

var result = (from result in dt.AsEnumerable()
              order by Guid.NewGuid()
              select result).Take(3); 

#10 楼

public static class IEnumerable
{
    static Random rng = new Random((int)DateTime.Now.Ticks);

    public static T RandomElement<T>(this IEnumerable<T> source)
    {
        T current = default(T);
        int c = source.Count();
        int r = rng.Next(c);
        current = source.Skip(r).First();
        return current;
    }

    public static IEnumerable<T> RandomElements<T>(this IEnumerable<T> source, int number)
    {
        return source.OrderBy(r => rng.Next()).Take(number);
    }
}

#11 楼

    public string LoadRandomNews(int maxNews)
    {
        string temp = "";

        using (var db = new DataClassesDataContext())
        {
            var newsCount = (from p in db.Tbl_DynamicContents
                             where p.TimeFoPublish.Value.Date <= DateTime.Now
                             select p).Count();
            int i;
            if (newsCount < maxNews)
                i = newsCount;
            else i = maxNews;
            var r = new Random();
            var lastNumber = new List<int>();
            for (; i > 0; i--)
            {
                int currentNumber = r.Next(0, newsCount);
                if (!lastNumber.Contains(currentNumber))
                { lastNumber.Add(currentNumber); }
                else
                {
                    while (true)
                    {
                        currentNumber = r.Next(0, newsCount);
                        if (!lastNumber.Contains(currentNumber))
                        {
                            lastNumber.Add(currentNumber);
                            break;
                        }
                    }
                }
                if (currentNumber == newsCount)
                    currentNumber--;
                var news = (from p in db.Tbl_DynamicContents
                            orderby p.ID descending
                            where p.TimeFoPublish.Value.Date <= DateTime.Now
                            select p).Skip(currentNumber).Take(1).Single();
                temp +=
                    string.Format("<div class=\"divRandomNews\"><img src=\"files/1364193007_news.png\" class=\"randomNewsImg\" />" +
                                  "<a class=\"randomNews\" href=\"News.aspx?id={0}\" target=\"_blank\">{1}</a></div>",
                                  news.ID, news.Title);
            }
        }
        return temp;
    }

#12 楼

IEnumerable<Customer> customers = this.ExecuteQuery<Customer>(@"SELECT top 10 * from [Customers] order by newid()");
customers.Dump();

SELECT top 10 * from [Customers] order by newid()

#13 楼

void Main()
{
    YourTable.OrderBy(v => Random()).FirstOrDefault.Dump();
}

[Function(Name = "NEWID", IsComposable = true)]
public Guid Random()
{
    throw new NotImplementedException();
}

#14 楼

var cust = (from c in ctx.CUSTOMERs.ToList() select c).OrderBy(x => x.Guid.NewGuid()).Taket(2);

#15 楼

public class DataContextProxy : IDataContext
{
    private readonly DataContext _context;

    public DataContextProxy(DataContext context)
    {
        _context = context;
    }

    // Snipped irrelevant code

    public IOrderedQueryable<T> Randomize<T>(IQueryable<T> query)
    {
        return query.OrderBy(x => _context.Random());
    }
}

var query = _dc.Repository<SomeEntity>();
query = _dc.Randomize(query);

public IOrderedQueryable<T> Randomize<T>(IQueryable<T> query)
{
    return query.OrderBy(x => Guid.NewGuid());
}