Diesel error type on Sql_Count

[NachoGotaki]

• Rust: cargo 1.31.0-nightly
• Diesel: 1.3.0
• Database: Mysql
• Operating System Ubuntu 18
• diesel:

Hello, first of all i have to say that im totally new in rust/rocket/diesel. Completely new.
Im only trying to print the total of rows in a query. Im doing this.

let total_results = places::table.count().load(connection); println!("{:?}", total_results);

Im trying to get the total to do a paginator, but compilation fails due to this:

error[E0282]: type annotations needed
--> src/v1/places/mod.rs:189:47
|
189 | let total_results = places::table.count().load(connection);
| ------------- ^^^^ cannot infer type for U
| |
| consider giving total_results a type

And in examples i see on the web they never give a type to the variable.
https://docs.diesel.rs/diesel/query_dsl/trait.QueryDsl.html#method.count

Thank in advance

[weiznich]

As far as I can see from that minimal code snippet, the problem seems to be that you use the result only in the print statement. Therefore rustc could not infer the concrete type of total_results because I only knows that those type has to implement a bunch of traits, but multiple types could fulfil that.
Therefore a explicit type annotation is needed here. (In the examples this is not the case because the assert_eq! explicitly puts a value (with a type) to compare in there.)

To make this work there are two solutions:

• Add a type annotation to the variable: let total_results: Result<Vec<i64>, _> = places::table.count().load(connection);
• Add the generic type parameter explicitly to the method call: let total_results = places::table.count().load::<i64>(connection);

(Closed this issue because our issue tracker should only contain actionable open issues. Feel free to ask such questions in our gitter channel or our forum

[NachoGotaki]

thank you too much.