Query very fast but mapping slow with dapper

Question

I'm using dapper for a new project and love it but I don't understand why my queries are really slow. The execution time is very fast, almost instant, but the connection stays open much longer while dapper is mapping the result to my object I guess.

Here is an example in glimpse :

This query is just a SELECT on something like 15 fields with a where on the primary key, so it's really fast to execute and it doesn't return that much of data. My code to execute it is :

 using (var conn = GetConnection())
 {
    obj = conn.Get<T>(id);
 }

And the object is a very basic poco with Strings and Ints. So why do I waste 220 ms doing this while the query execution itself takes 3 ms ? Where is the difference ?

Thanks for your help !

Answer 1

UPDATE

There was one field that was causing problems for me in the selection part of my SQL statement. I just went by removing each field one by one and then found the one which was causing the problem.

I had to cast one of my fields to nvarchar like this:

CAST(my_field AS nvarchar(max)) as my_field

ORIGINAL ANSWER

It has to do something with the mapping. Because if I change it from "Strongly Typed" (which is taking for ever, almost 1 minute):

var products = connection.Query<Product>(sql).ToList();

to "Anonymous":

var products = connection.Query(sql).ToList();

then it executes really fast (1 second).

I tried and executed the SQL statement directly in "SQL Server Management Studio" as a query and it finishes in less then 1 second.

So my suggestion is, that you use the "anonymous mapping" until dapper guys fix this if they will be able to.

Answer 2

I had a similar experience with Dapper as I was trying to project from a View to an POCO object.

The problem ended up being for me that I did not have a column for each property on my object, so the Convert.ChangeType() was very slow, I added a column to my View that would always return NULL, and the Query<T>() call sped up dramatically.