Dynamic Searching using LINQ - Dataset + Joins

re: Dynamic Searching using LINQ - Dataset + Joins

Dreamn — Mon, 27 Jul 2009 18:29:20 GMT

why so much of hassle just write the basic query and append where depending on condition

IEnumerable<Foo> query =null;

if (!string.IsNullOrEmpty(_paramsCol[4]))

{

query = li.Where(x => x.SomeField == _paramsCol[4]);

}

if (!string.IsNullOrEmpty(_paramsCol[5]))

{

query = li.Where(x => x.SomeField == _paramsCol[5]);

}

re: Dynamic Searching using LINQ - Dataset + Joins

Jonathan Aneja — Mon, 27 Jul 2009 22:03:50 GMT

Well when you say "x => x.SomeField" - the property "SomeField" has to be known *statically* - you can't change that at runtime.

By using the DynamicCondition API, you can have the name of the field picked *dynamically* at runtime using only one line of code (db.Orders.CreateCondition(...)).

For example if a user has a search form where they could search by any field, you'd have to write a *lot* of if/else stuff to cover every possible case, and every time you add a field to your table you'd need to update this logic.

For more information on the scenario please see the previous blog entry on this topic: http://blogs.msdn.com/vbteam/archive/2007/08/29/implementing-dynamic-searching-using-linq.aspx

Hope that helps!

Jonathan Aneja

Program Manager, VB Team

re: Dynamic Searching using LINQ - Dataset + Joins

Jaideep — Thu, 06 Aug 2009 09:17:12 GMT

avery good article.... just wanted to know, if we can get a c# version of this. i tried converting it to c# but it is giving compile errors

re: Dynamic Searching using LINQ - Dataset + Joins

Jonathan Aneja — Fri, 07 Aug 2009 03:14:12 GMT

Hey Jaideep,

Can you post the compile errors that you're seeing? When people have translated this in the past the only error I've seen is that some of the calls to GetType() are partially qualified whereas C#'s typeof() requires full namespace qualification. That might be the issue.

Hope that helps!

Jonathan

re: Dynamic Searching using LINQ - Dataset + Joins

Michal Rovnanik — Wed, 21 Oct 2009 19:44:36 GMT

Hi Jonathan,

thanks for all the code, I appreciate it. I face a problem with dynamic query construction in my application. I load data into datatables in runtime (from xml, csv, sql server and nsf) along with joins definition among the tables.

Sample code (just a trial one):

Dim personnel As DataTable = Me.iDataset.Tables(0)

Dim workrecords As DataTable = Me.iDataset.Tables(1)

Dim query = _

From per In personnel _

From wr In workrecords

Dim condition1 = query.CreateMultiColumnCondition( _

"per.OSCIS", Compare.Equal, "wr.OSCIS")

Calling CreateMultiColumnCondition causes an exception like this:

"Public member 'CreateMultiColumnCondition' on type '<SelectManyIterator>d__31(Of DataRow,DataRow,VB$AnonymousType_0(Of DataRow,DataRow))' not found."

It implies some kind of type casting error. Where am I going in wrong? The dataset is not strongly-typed one.

Thanks very much, any help is appreciated

Michal