如何使用Orderby创建动态linq查询？

Question

I have linq query which is as follows

string sortby="Date"; //it can be name or something else as well

var query=(from t in Uow.Transactions.GetAllWithReferences()
           orderby t.Date descending
           select t);

But I want to orderby differently based on sortby variable value. How can i do that using Linq?

Answer 1

Using reflection:

string sortby="Date" //it can be name or something else as well

var query=(from t in Uow.Transactions.GetAllWithReferences()
           orderby t.GetType().GetProperty(sortby).GetValue(t, null) descending
           select t);

Answer 2

For sample class:

private class Tst
{
    public int field1 { get; set; }

    public string field2 { get; set; }

    public string field3 { get; set; }
}

You can do it this way:

var index = 1;

var sortedList = (from l in list
                  orderby index == 1 ? l.field1.ToString() : index == 2 ? l.field2 : l.field3  
                  select l);

But as fields have different types you have to do some type cast as you see l.field1.ToString()

Way you do it using lambda is:

var sortedList =
    list.OrderBy(l => 
            index == 1 ? l.field1.ToString() 
            : index == 2 ? l.field2 
            : l.field3)
        .Select(l => l).ToList();

Answer 3

If you use the OrderBy() LINQ extension method, you can pass in a predicate which could be something like (untested):

Predicate orderByClause;
if ( blah == "date" )
    orderByClause = { order => order.Date };

if ( blah == "something else" ) 
    orderByClause = { order => order.SomethingElse };

var oSortedList = oResultList.OrderBy( orderByClause );

I'm sure the syntax if way off, but I have done something like this before...

Hope this helps!

Answer 4

你可以使用一个库，这是我最喜欢的一个： http ： //dynamite.codeplex.com/