Ron Jacobs

Windows Workflow Foundation

How to use LINQ in a Workflow

How to use LINQ in a Workflow

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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)



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.



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
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?



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