How to create a property (collection) expression selector from a string?

Question

I wanted to transform the string "Employee.Orders.OrderID" in the linq expression: "employee.Orders.Select(order => order.OrderID)".

I already know how to do this in simple properties such as "Employee.FirstName" my question is how to do this in properties within a type within a collection.

"Order" is a collection of orders in the class "Employee". "OrderID" is a property of the class "Order".

In other words, I want to transform this;

string path = "Employee.Orders.OrderID";

Into this;

Expression<Func<Employee, object>> exp = employee => employee.Orders.Select(order => order.OrderID);

JulianR · Accepted Answer · 2012-11-26 17:31:16Z

3

This should do the trick:

https://gist.github.com/4149424

I haven't compiled the resulting expression, but it builds the expression without an exception.

EDIT: I've added a line to create the lambda and compile it too, which it does, so it works.

It handles your scenario where you access a property of a collection Orders.OrderID, which is the part that makes it sort of complicated. Without it, it would be about 30 lines shorter.

Currently, what it does is split the string on '.' and then it recursively processes every element. If the element is IEnumerable (but not a string) it builds an additional Select lambda.

It also handles a slightly more complex (but more of the same) scenario where you access a collection property in a collection property.

edited Nov 26, 2012 at 17:31

answered Nov 26, 2012 at 17:19

JulianR

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3 Comments

Luis Over a year ago

I have not had time to test, but it was very good, thanks. I'll do some testing in a few hours and come back here if it works to confirm your answer.

Luis Over a year ago

So I came back here to thank for your help, your answer worked perfectly. You helped an open source project to become even better, if you or anyone wants to know more about the project look here: tgh.codeplex.com

JulianR Over a year ago

Glad I could help :) Good luck on the project! I have a similar-ish project (github.com/JulianR/ThisMember/wiki more similar to Automapper than your library) that does lots of stuff with expressions, hence why I knew this.

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