How to use LINQ in a Workflow - Ron Jacobs - Site Home

Question

Can I use a LINQ Query such as the following in a Workflow?

private static void ShowQueryWithCode(IEnumerable<string> names)
{
    Console.WriteLine("Linq Query in Code - show names that start with 'R'");

    // Assuming there are no null entries in the names collection
    var query = from name in names where name.StartsWith("R") select name;

    // This is the same thing as 
    // var query = names.Where(name => name.StartsWith("R"));

    foreach (var name in query)
    {
        Console.WriteLine(name);
    }

    Console.WriteLine();
}

Answer

Yes, you can use LINQ with a Workflow in exactly the same way.

Download Sample Code

Step 1: Create a Workflow with an In Argument of type IEnumerable<string>

Here you can see that I've added the in argument

Step 2: Add a Variable for the query of type IEnumerable<string>

Before you can add a variable you need to include an activity which has variables. In this workflow I've added a sequence.

Step 3: Assign the query the LINQ expression you want to use

You can use a method chain or query syntax.

Step 4: Iterate over the collection

In the completed workflow I used a ForEach<string> activity to iterate the list of names and write them to the console.

Summary

This example uses C# in .NET 4.5 but the same technique can be used with Visual Basic.

When you run it you can see that both methods work the same.

Happy Coding!

Ron Jacobs
http://blogs.msdn.com/rjacobs
Twitter: @ronljacobs

Hi Ron,

Sorry to post my question under this topic, as I am not sure where i can post my question without searching the blogs.

Here i go..

I am creating workflows dynamically for each project based on the tasks defined for projects in database. Its working fine as long as i don't modify the tasks for any project like adding new task and removing the existing task for the workflow tree for a project. When I make changes to the workflow tree that time I see error msg like 'workflow tree is not matching with persisted instance'.

To make it more clear:

1. I am creating workflow pro-grammatically based on the tasks defined in database for a project.

2. During the execution of project, I am adding new task or removing task from the that particular project in database

3. When i resume and load the instance with new modified workflow tree schema, it throws error.

My Question is :

How can i handle such situation with same instance ID?

Regards,

Mahendra