`AsChangeset` requires prelude

[jethrogb]

When deriving AsChangeset on a simple table, e.g.

use schema::posts;

#[derive(AsChangeset)]
pub struct Posts {
    pub id: i64,
}

I'm getting

error: no method named `eq` found for type `schema::posts::columns::id` in the current scope
 --> .../diesel_demo/src/lib.rs:4:1
  |
4 | include!(concat!(env!("OUT_DIR"), "/lib.rs"));
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: the method `eq` exists but the following trait bounds were not satisfied: `schema::posts::columns::id : std::iter::Iterator`
  = help: items from traits can only be used if the trait is in scope; the following trait is implemented but not in scope, perhaps add a `use` for it:
  = help: candidate #1: `use diesel::ExpressionMethods`
  = note: this error originates in a macro outside of the current crate