main.rs

#[macro_use]
extern crate diesel;

use diesel::{
    prelude::*, query_builder::{InsertStatement, UndecoratedInsertRecord},
    query_dsl::methods::ExecuteDsl,
};

trait LoadTable {
    type Insertable;

    fn fetch_data() -> Vec<Self::Insertable>;

    fn populate_table<T>(conn: &PgConnection, table: T)
    where
        T: Table,
        for<'a> &'a [Self::Insertable]: UndecoratedInsertRecord<T> + Insertable<T>,
        for<'a> InsertStatement<T, <&'a [Self::Insertable] as Insertable<T>>::Values>:
            ExecuteDsl<PgConnection>,
    {
        let data = Self::fetch_data();
        data.insert_into(table).execute(conn).unwrap();
    }
}

table! {
    blah (id) {
        id -> Int4,
        value -> Int4,
    }
}

#[derive(Debug, Insertable)]
#[table_name = "blah"]
struct Blah {
    value: i32,
}

struct A;

impl LoadTable for A {
    type Insertable = Blah;
    fn fetch_data() -> Vec<Self::Insertable> {
        vec![Blah { value: 1 }]
    }
}

fn main() {
    let conn = PgConnection::establish("abc").unwrap();
    A::populate_table(&conn, blah::table);
}

// returns...
// [Running cargo check]
//     Checking diesel_bound v0.1.0
// error[E0271]: type mismatch resolving `for<'a> <std::option::Option<diesel::expression::operator
// s::Eq<blah::columns::value, diesel::expression::bound::Bound<diesel::sql_types::Integer, &'a i32
// >>> as diesel::Insertable<blah::table>>::Values == diesel::query_builder::ValuesClause<_, blah::
// table>`
//   --> src/main.rs:50:5
//    |
// 50 |     A::populate_table(&conn, blah::table);
//    |     ^^^^^^^^^^^^^^^^^ expected bound lifetime parameter 'a, found concrete lifetime
//    |
//    = note: required because of the requirements on the impl of `diesel::Insertable<blah::table>`
//  for `(std::option::Option<diesel::expression::operators::Eq<blah::columns::value, diesel::expre
// ssion::bound::Bound<diesel::sql_types::Integer, &i32>>>,)`
//    = note: required because of the requirements on the impl of `for<'a> diesel::query_builder::Q
// ueryFragment<diesel::pg::Pg>` for `diesel::insertable::BatchInsert<'a, Blah, blah::table>`
//    = note: required because of the requirements on the impl of `for<'a> diesel::query_builder::Q
// ueryFragment<diesel::pg::Pg>` for `diesel::query_builder::InsertStatement<blah::table, diesel::i
// nsertable::BatchInsert<'a, Blah, blah::table>>`
//    = note: required because of the requirements on the impl of `for<'a> diesel::query_dsl::load_
// dsl::ExecuteDsl<diesel::PgConnection, diesel::pg::Pg>` for `diesel::query_builder::InsertStateme
// nt<blah::table, <&'a [Blah] as diesel::Insertable<blah::table>>::Values>`
// note: required by `LoadTable::populate_table`
//   --> src/main.rs:14:5
//    |
// 14 | /     fn populate_table<T>(conn: &PgConnection, table: T)
// 15 | |     where
// 16 | |         T: Table,
// 17 | |         for<'a> &'a [Self::Insertable]: UndecoratedInsertRecord<T> + Insertable<T>,
// ...  |
// 22 | |         data.insert_into(table).execute(conn).unwrap();
// 23 | |     }
//    | |_____^
//
// error: aborting due to previous error
// //