Prototyping LINQ using LINQPad
Posted by Ronnie Holm on June 29th, 2008
I’ve been doing some LINQ development lately. What I typically do is write a LINQ query within the production code and then attach a debugger to see what the query returns and perhaps what the underlying SQL statement looks like. For simple queries this technique is sufficient, but for more complex ones, several, cumbersome round-trips through the debugger are often necessary to get the query right.
Researching the issue I came across LINQPad (see LINQPad in action). The tool is a generic testbed for molding expressions or statements (LINQ being one such class) before embedding them into code. Also, because LINQPad is written by one of the authors of C# in a Nutshell, the tool comes with a lot of samples from the book.
On the implementation side, LINQPad works by emitting MSIL behind the scenes, conceptually similar to the DataContext classes generated by Visual Studio when using the database design surface.
As an interesting side note, LINQPad can also show the query after it has been transformed into lambdas, anonymous types, and the like:
Users
.Join (
Macs,
u => u.UserId,
m => m.UserId,
(u, m) =>
new
{
u = u,
m = m
}
)
.Where (temp0 => (temp0.u.Created < DateTime.Now.AddHours (-24)))
.Select (
temp0 =>
new
{
UserId = temp0.u.UserId,
UserCreated = temp0.u.Created,
Mac = temp0.m.Mac,
Active = temp0.m.Active
}
)
.Take (15)
Keep in mind how the .Net 3.5 framework and the .Net 3.5 compiler play together to ultimately transform the LINQ query into MSIL. What the framework does is transform the LINQ query into the above expression by applying a transform to the abstract syntax tree of the LINQ query. The .Net 3.5 compiler then transforms the lambdas, the anonymous types, and the like into .Net 2.0 MSIL (there’s no such thing as a .Net 3.5 CLR. For an overview of how the various versions of the framework, the compiler, and the CLR relate to each other, see Scott Hanselman’s blog entry).
But back to LINQPad. The only downside that I’ve encountered is that there’s no IntelliSense support in the current 1.24 release. However, even without IntelliSense support LINQPad is still a very valuable tool.
October 19th, 2010 at 9:28 am
[...] You’d typically rely on type inference and the var keyword for declaring the type of the result. But to make LINQ more transparent I’ll explicitly state the return type. At the same time I’ll transform the query expression syntax into lambda expression syntax. What the compiler would otherwise do is transform each standard query operator, such as Where and Select, into a corresponding method call on the collection, passing in a lambda expression. Both representations are semantically equivalent, but for this simple query the lambda expression syntax appears more complex. This is generally not the case for either representation as you can see with a tool like LINQPad. [...]