LINQ Dynamic Queries

I came across an article this morning that helped me with a LINQ query issue that I was trying to work through regarding dynamic queries.

 

http://www.rocksthoughts.com/blog/archive/2008/01/24/linq-to-sql-dynamic-queries.aspx

 

My situation was very similar; however, in my case I was querying an ENTITY rather than SQL directly; however, the same rules applied.

 

I knew I could easily write a query that was not type safe and not checked at compile time; however, the thought of doing that really bothered me because I wanted to leverage the full power of LINQ and keep everything type safe and checked at compile time.

 

I ended up taking advantage of Lambda Expressions:

Public Function Search(ByVal Name As String, ByVal City As String) As IEnumerable(Of MyTable)
     Dim MyEntities As New DbEntities()
     Dim MyQuery As ObjectQuery(Of MyTable) = MyEntities.MyTableSet
     Dim MyResults = From x In MyQuery Select x

     If Not IsBlank(Name) Then
          MyResults = MyResults.Where(Function(e) e.Name.Equals(Name))
     End If

 

     If Not IsBlank(City) Then
          MyResults = MyResults.Where(Function(e) e.City.Equals(City))
     End If

     Return MyResults.AsEnumerable
End Function

 

More information on Lambda Expressions can be found here:

 

http://weblogs.asp.net/scottgu/archive/2007/04/08/new-orcas-language-feature-lambda-expressions.aspx