CODEWITHSUNDEEP
c#workflow-foundationrule-engine
bdwakefield
bdwakefield

Reputation: 705

Is it possible to use a LINQ Query in Windows Workflow rule condition?

I am in the process of prototyping an implementation of a rules engine to help us with our ordering portals. For example giving discounts on items or requiring approval if certain items are ordered. We would also like to be able to add rules for dollar amounts, user hierarchy positions, and be apply it one client or more.

I feel that WWF is a good answer to this need.

All of that said however I am having a little difficulty figuring out how best to set up some of the more complex rules. I have a "condition" that I feel is best described in a LINQ query, like so:

var y = from ol in currentOrder.OrderLines where ol.ItemCode == "MYITEMCODE" select ol;

I am not against using a different framework for a rules engine or adding additional properties/methods to our objects (ex: OrderHasItem(ItemCode), etc) to make these rules more simplified but I would like to avoid having to do that. It feels self-defeating in that it forces us down the road of potentially requiring code changes for new rules.

Upvotes: 1

Views: 2351

Answers (2)

Kizz
Kizz

Reputation: 799

WF is a workflow engine. It's used to run factories and banks. The rule engine is just a small part of it. To make sense, any normal WF project requires a dedicated team of professionals to build it. Seems like an overkill for your specific purpose. You are very likely to bury yourself and your project in a typical fight between requirements and real skills of your team.

The use of any available .NET engine would be more justified in your situation. Keep in mind that building a custom rule engine is not an easy tasks, no matter how simple it seems from the beginning. Setting property values of a class (typically called a "fact" or "source" object) or executing actions (invoking class' methods) is what rules engines do best. And it seems that it's exactly what you need. Check out some available .NET engines. They are inexpensive, if not free, and reliable.

Upvotes: 0

Ron Jacobs
Ron Jacobs

Reputation: 3279

Yes, you can use Linq queries with Workflow. In WF what you are referring to as a rule is an expression that is evaluated at runtime. Your query is selecting a subset of the orderliness based on a criteria.

For example, if I have a collection of names and I want to see only names that begin with 'R'. I could write the following code.

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();
}

To do the same with Workflow

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

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

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

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

variable

Step 3: Assign the query the LINQ expression you want to use You can use a method chain or query syntax.

expression

Step 4: Iterate over the collection

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

Workflow1

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

You can download the sample code here

Upvotes: 3

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