Non-parameter SQL Variables with MySql Connector/Net and Dapper?

I don't think this is a dapper issue; dapper just takes the SQL you offer, and adds any members from the "args" object that it obviously see in the SQL.

The way to investigate this is to try running the same with DbCommand directly - my guess is that it will fail identical. There is going to be some SQL trick to make it work, but that is between you and MySQL. All dapper is doing is:

creating a command with your sql defining a parameter called "Slug" and setting the value invoking the sql and parsing the results

it doesn't touch "ID", and it is correct that it doesn't do so.

Answers

It turns out "MySql Connector/Net" generates the error.

In order to use Non-parameter SQL Variables with MySql Connector/Net, you have to add the following option to your connection string:

"Allow User Variables=True"

See: http://blog.tjitjing.com/index.php/2009/05/mysqldatamysqlclientmysqlexception-parameter-id-must-be-defined.html

Answers

You need to declare the ID variable in your sql code:

var sql = @"DECLARE @ID Int; 
            SELECT @ID := id, slug, Title, Text FROM posts WHERE slug = @Slug;
            SELECT * FROM comments where postid = @ID;";