could not find schema in the crate root

[jiangxiaoqiang]

when I am using schema like this in the main.js:

use crate::schema::posts;

fn main(){
    // use reddwarf_music::schema::posts::dsl::*;
    let connection = config::establish_connection();
}

shows:

~/Documents/GitHub/reddwarf_music on  develop! ⌚ 13:58:24
$ cargo build                                                                           ‹ruby-2.7.2›
   Compiling reddwarf_music v0.1.0 (/Users/dolphin/Documents/GitHub/reddwarf_music)
error[E0432]: unresolved import `crate::schema`
  --> src/main.rs:26:12
   |
26 | use crate::schema::posts;
   |            ^^^^^^ could not find `schema` in the crate root

warning: unused import: `serde::Deserialize`
 --> src/biz/user/user.rs:3:5
  |
3 | use serde::Deserialize;
  |     ^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0432`.
error: could not compile `reddwarf_music`

To learn more, run the command again with --verbose.
(base) 

what should I do to fix this problem?