My goal is to query the database and find if a user already exists with the giving email. Looking at the documentation, this appears the way to do so. The only difference is I want to query based on the email instead of the name of the user.
I have some code like this:
src/models.rs
use crate::schema::mailing_list;
use chrono::NaiveDateTime;
use diesel::prelude::*;
use diesel::Insertable;
#[derive(Queryable, Insertable)]
#[diesel(table_name = mailing_list)]
pub struct Subscriber {
pub uuid: String,
pub email: String,
pub date_subscribed: NaiveDateTime,
pub date_unsubscribed: Option<NaiveDateTime>,
}
and some logic here that has been shortened:
src/mail.rs
use chrono::Utc;
use diesel::prelude::*;
use diesel::dsl::select;
use diesel::dsl::exists;
use rocket::http::Status;
use uuid::Uuid;
use crate::db;
use crate::models::Subscriber;
use crate::schema::mailing_list::dsl::mailing_list;
#[get("/subscribe?<email>")]
pub fn subscribe(email: String) -> Status {
(...)
let connection = &mut db::establish_connection();
(...)
let email_exists = select(exists(mailing_list.filter(email.eq(&email))))
.get_result(connection);
(...)
}
Compiling rocket-website v0.1.0 (/home/cedric/Documents/Programming/personal-website/rocket-website)
error[E0277]: the trait bound `bool: diesel::Expression` is not satisfied
--> src/mail.rs:27:58
|
27 | let email_exists = select(exists(mailing_list.filter(email.eq(&email))))
| ------ ^^^^^^^^^^^^^^^^ the trait `diesel::Expression` is no
t implemented for `bool`
| |
| required by a bound introduced by this call
|
= help: the following other types implement trait `diesel::Expression`:
&'a T
(T0, T1)
(T0, T1, T2)
(T0, T1, T2, T3)
(T0, T1, T2, T3, T4)
(T0, T1, T2, T3, T4, T5)
(T0, T1, T2, T3, T4, T5, T6)
(T0, T1, T2, T3, T4, T5, T6, T7)
and 80 others
= note: required for `SelectStatement<FromClause<table>>` to implement `FilterDsl<bool>`
= note: 1 redundant requirement hidden
= note: required for `table` to implement `FilterDsl<bool>`
note: required by a bound in `diesel::QueryDsl::filter`
--> /home/cedric/.cargo/registry/src/github.com-1ecc6299db9ec823/diesel-2.0.3/src/query_dsl/mod.rs:619:15
|
619 | Self: methods::FilterDsl<Predicate>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `diesel::QueryDsl::filter`
The error is quite longer than the snippet above, but in short it mentions that for line 27 (the line with the select and the exists these errors:
the trait `diesel::Expression` is not implemented for `bool`
the trait `ValidGrouping<()>` is not implemented for `bool`
the trait `expression::subselect::ValidSubselect<NoFromClause>` is not implemented for
`SelectStatement<FromClause<table>, query_builder::select_clause::DefaultSelectClause<FromClause<table>>,
query_builder::distinct_clause::NoDistinctClause, query_builder::where_cl
ause::WhereClause<bool>>`
the trait `expression::subselect::ValidSubselect<NoFromClause>` is not implemented for
`SelectStatement<FromClause<table>, query_builder::select_clause::DefaultSelectClause<FromClause<table>>,
query_builder::distinct_clause::NoDistinctClause, query_builder::where_clause::WhereClause<bool>>`
Additionally, there's this other error:
error[E0277]: the trait bound `bool: QueryId` is not satisfied
--> src/mail.rs:28:21
|
28 | .get_result(connection);
| ---------- ^^^^^^^^^^ the trait `QueryId` is not implemented for `bool`
| |
| required by a bound introduced by this call
where this line also triggers this version of the error:
the trait `QueryFragment<Mysql>` is not implemented for `bool`
The filter function expects a special type from diesel that comes from an auto-generated type in the crate::schema namespace.
This should do the trick:
let email_exists = select(exists(mailing_list.filter(self::schema::mailing_list::dsl::email.eq(&email))))
.get_result::<bool>(connection);