Question

I have a Task object that has a collection of Label objects … in the database the tables are called Task and Label.

There are a variety of ways to search for a Task, so using LINQ, I construct my LINQ query in an expression tree … similar to the below code sample:

IQueryable<Data.Task> query = ctx.DataContext.Tasks;      if (criteria.Number > 0)         query = query.Where(row => row.Number == criteria.Number);    if (criteria.CustomerId != Guid.Empty)     query = query.Where(row => row.Project.CustomerId == criteria.CustomerId);  if (criteria.ProjectId != Guid.Empty)     query = query.Where(row => row.ProjectId == criteria.ProjectId);  var data = query.Select(row => TaskInfo.FetchTaskInfo(row));  this.AddRange(data);  

This works great … but now I would like to search for Tasks with a specific Label, for example, accounting or feature-request.

I am able to do this in LINQPad from a complete query:

from t in Tasks join l in Labels on t.TaskId equals l.SourceId  where l.Name == 'accounting' select t 

Is there anyway to do this using an expression tree? I’m stuck! Any help would be greatly appreciated!

Answer 1

I believe this should do it:

Tasks.Join(Labels.Where(l => l.Name == 'accounting'), t => t.TaskId, l => l.SourceId, (t, l) => t)