Prepared Statement on Postgresql in Rails

Question

Right now I am in the middle of migrating from SQLite to Postgresql and I came across this problem. The following prepared statement works with SQLite:

id = 5
st         


        

Answer 1

If you want to use prepare like that then you'll need to make a couple changes:

1. The PostgreSQL driver wants to see numbered placeholders ($1, $2, ...) not question marks and you need to give your prepared statement a name:

    ActiveRecord::Base.connection.raw_connection.prepare('some_name', "DELETE FROM my_table WHERE id = $1")
   

2. The calling sequence is prepare followed by exec_prepared:

   connection = ActiveRecord::Base.connection.raw_connection
   connection.prepare('some_name', "DELETE FROM my_table WHERE id = $1")
   st = connection.exec_prepared('some_name', [ id ])
   

The above approach works for me with ActiveRecord and PostgreSQL, your PG::Connection.open version should work if you're connecting properly.

Another way is to do the quoting yourself:

conn = ActiveRecord::Base.connection
conn.execute(%Q{
    delete from my_table
    where id = #{conn.quote(id)}
})

That's the sort of thing that ActiveRecord is usually doing behind your back.

Directly interacting with the database tends to be a bit of a mess with Rails since the Rails people don't think you should ever do it.

If you really are just trying to delete a row without interference, you could use delete:

delete()

[...]

The row is simply removed with an SQL DELETE statement on the record’s primary key, and no callbacks are executed.

So you can just say this:

MyTable.delete(id)

and you'll send a simple delete from my_tables where id = ... into the database.