如何提取order by子句，以便我可以使用逻辑来设置它？

Question

I want to extract out an OrderBy clause, is this possible?

So I can do something like:

OrderBy ob = null;

if(....)
  ob = x.Id
else
  ob = x.Name


var result = source.OrderBy(ob);

Is this possible?

Answer 1

You could do something that would map almost exactly to what you're doing, but the easier option is to keep track of the query, not the method to order on:

IQueryable<Whatever> query = someQuery;

if(something)
    query = query.OrderBy(item => item.Id);
else
    query = query.OrderBy(item => item.Name);

However, if you really want to:

Expression<Func<Whatever, object>> selector = null;

if(something)
    selector = item => item.Id;
else
    selector = item => item.Name;

var results = query.OrderBy(selector);

Answer 2

You could try something like this:

IQueryable<Foo> result = source ...
if(....)
  result = result.OrderBy(x => x.Id);
else
  result = result.OrderBy(x => x.Name);

Answer 3

Why not just do your conditional logic and do the separate OrderBy() based on the conditon?

Ex.

if(foo == true)
{
result = result.OrderBy(r => r.Id);
}
else
{
result = result.OrderBy(r => r.Name);
}