Build dynamic LINQ?

Question

I\'m using LINQ to query data. Consider a case where the user only wants to report on say 1 of the 3 fields? (see below)

Can anyone tell me how to build the query d

Answer 1

We do it by passing in a Criteria object and then build the query by appending the desired criteria using expression trees.

IQueryable query = ctx.DataContext.Stories;

if (criteria.StoryId != null) // StoryId
    query = query.Where(row => row.StoryId == criteria.StoryId);

if (criteria.CustomerId != null) // CustomerId
    query = query.Where(row => row.Project.CustomerId == criteria.CustomerId);

if (criteria.SortBy != null) // SortBy
    query = query.OrderBy(criteria.SortBy + " " + criteria.SortOrder.Value.ToStringForSql());

if (criteria.MaximumRecords != null) // MaximumRecords
    query = query.Take(criteria.MaximumRecords.Value);

var data = query.Select(row => StoryInfo.FetchStoryInfo(row));

You can also take a look at the Dynamic Linq library at http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx