Comments for Progressive Digressive

Comment on Dynamic Linq with Expression Trees by Jhelumi

Jhelumi — Thu, 24 Feb 2011 17:00:46 +0000

I need something like this for my Advance Search form. What I’m doing is passing the rules collection to a method which uses the foreach loop to apply all the where conditions to my object. my question is how I’m going to return the results.
public IQueryable GetProducts(List rules)
{
foreach( var rule in rules_
{ var products = this.ObjectContext.Products.Where(GetExpression(
rule.MemberName, // The Applicant property
rule.Operator, // Equals, Contains, GreaterThan, etc
rule.Value)
);
}
return ??
}

How can I make the query to run and return the result

Comment on Dynamic Linq with Expression Trees by Shane

Shane — Wed, 08 Dec 2010 19:58:07 +0000

If i use Equal instead of Equals for the operator type, everything works just fine.

Comment on Dynamic Linq with Expression Trees by Shane

Shane — Tue, 07 Dec 2010 23:15:18 +0000

Interesting note:

decimal? testVal = new decimal?(2100);
var test = (from i in context.Leases where i.AnnualRental == testVal select i).ToList();

the above works, while the following throws an error:

decimal? testVal = new decimal?(2100);
var test = (from i in context.Leases where i.AnnualRental.Equals(testVal) select i).ToList();

Unable to create a constant value of type ‘System.Object’. Only primitive types (‘such as Int32, String, and Guid’) are supported in this context.
Source : System.Data.Entity

Comment on Dynamic Linq with Expression Trees by Shane

Shane — Tue, 07 Dec 2010 23:04:31 +0000

I am using Entity Framework and have an entity with a nullable decimal field. When I attempt to call this method on that field I get this error:

Expression of type ‘System.Nullable`1[System.Decimal]‘ cannot be used for parameter of type ‘System.Object’ of method ‘Boolean Equals(System.Object)’

It appears to be related to the fact that EF cannot handle the Object parameter. I am not sure if this is just an issue with Linq to EF or not.

As an example this will also give an error:

decimal? testVal = new decimal?(2100);
var test = (from i in context.Leases where i.AnnualRental.Equals(testVal) select i).ToList();

Comment on Dynamic Linq with Expression Trees by Marcus

Marcus — Tue, 07 Dec 2010 22:22:10 +0000

I’m not sure what you mean Shane, it seems to work ok with nullable props too for me. Using that same method to create the expression, I just pass in a nullable property and it all works.

Is there a specific example you can give?

Comment on Dynamic Linq with Expression Trees by Shane

Shane — Tue, 07 Dec 2010 21:53:16 +0000

I appreciate your example and it works great with non-nullable fields, however I am having fits trying to make this work with nullable fields. Any suggestions?

Comment on Dynamic Linq with Expression Trees by Marcus

Marcus — Wed, 02 Dec 2009 23:28:05 +0000

In the UI you show, how do you select both London & NY. That doesn’t seem to work the code either.

That’s not yet a requirement, but if/when it is, I’d need to introduce some logic like PredicateBuilder in the back end, and some optional rule grouping by ‘OR/AND’ in the client UI to enable it.

Comment on Dynamic Linq with Expression Trees by Aaron Goldman

Aaron Goldman — Wed, 02 Dec 2009 20:36:12 +0000

This is a cool demonstration of expression tree building. I have to do this sometime.

I have almost the exact same requirement in my current project. My data is in arrays, so in a way its more straightforward.

I created 2 filter types – 1 for enums and 1 for range filtering. Everything is bound to a WPF UI so when the user selects the field, they’re also selecting the index into the array (as a property of the Field type). Also, the user selects in a slider for ranges and a list for enums. In the UI you show, how do you select both London & NY. That doesn’t seem to work the code either.

In the end, my filtering in Linq looks very similar to yours and the whole system is nearly logically identical.

Comment on .NET Development on a Mac – Fusion or Parallels? by Marcus

Marcus — Sat, 26 Sep 2009 18:23:51 +0000

I'm running 10.5.8, and Windows 7 64-bit (I originally went for 64 bit due to a note on the VMware blog noting some people were getting better performance out of 64-bit). Do you have enough RAM? You could always install under Bootcamp, then get Parallels to just mount your Bootcamp partition - that way it's potentially the best of both worlds. For more intensive work you can run natively, for regular stuff just run in the VM. Was the 'Slow Leopard' pun intentional? :)

Comment on .NET Development on a Mac – Fusion or Parallels? by Danish Munir

Danish Munir — Sat, 26 Sep 2009 17:52:15 +0000

Thanks for sharing that.
Where you using 10.5 or 10.6? I’m trying the same thing on a brand new Macbook Pro 15″ 2.53 Ghz running Slow Leopard and both Parallels and Fusion are painfully slow. I’ve tried both Win 7 and Win Xp.

Whats a developer to do?