How can I use the sql function CAST in rust, diesel? - mysql

Question

I'm developing a new endpoint using Rocket and am trying to return a Vec<> made of various structs.
The raw query I want to replicate in diesel is:
select location.id, location.name, w.datetime, t.temp, w.compass, w.speed, r.probability, s.height
from location
inner join rainfall r on location.id = r.location
inner join temperature t on location.id = t.location
inner join wind w on location.id = w.location
inner join swell s on location.id = s.location
where t.datetime = w.datetime
and s.datetime = t.datetime
and CAST(t.datetime as date) = CAST(r.datetime as date)
and t.datetime > now() and t.datetime < NOW() + INTERVAL 1 HOUR;
and I recognize, that in order to use the CAST function I need to use the sql_function! macro:
sql_function! {
#[sql_name="CAST"]
fn cast(x: sql_types::Nullable<sql_types::Datetime>) -> sql_types::Date;
}
which allows me to create the following query:
let summaries: Vec<(Location, Swell, Wind, Temperature, Rainfall)> = location::table
.inner_join(swell::table)
.inner_join(wind::table)
.inner_join(temperature::table)
.inner_join(rainfall::table)
.filter(temperature::datetime.eq(wind::datetime))
.filter(temperature::datetime.eq(swell::datetime))
.filter(temperature::datetime.gt(utilities::today()))
.filter(temperature::datetime.lt(utilities::future_hour(1)))
.filter(cast(temperature::datetime).eq(cast(rainfall::datetime)))
.load(&conn.0)?;
However, when I run this query I get a SQL Query error:
"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near \') = CAST('rainfall'.'datetime')\' at line 1"
As illustrated in the raw SQL statement it should read CAST('rainfall'.'datetime' as date).
My question is, how can I add the 'as date' component to my diesel query? Is something missing in the sql_function definition?
Thanks for your help.

Answer 1

I found the answer after digging a little deeper into similar questions.
Turns out you can enter a raw sql string into the .filter method after adding: use diesel::expression::sql_literal::sql;.
So the final snippet becomes:
let summaries: Vec<(Location, Swell, Wind, Temperature, Rainfall)> = location::table
.inner_join(swell::table)
.inner_join(wind::table)
.inner_join(temperature::table)
.inner_join(rainfall::table)
.filter(temperature::datetime.eq(wind::datetime))
.filter(temperature::datetime.eq(swell::datetime))
.filter(temperature::datetime.gt(utilities::today()))
.filter(temperature::datetime.lt(utilities::future_hour(1)))
.filter(sql("CAST(`temperature`.`datetime` as date) = CAST(`rainfall`.`datetime` as date)"))
.load(&conn.0)?;
I hope this helps someone else!