I cannot make binding work with Diesel on MariaDB

Question

I simply wanted to pass an argument to my sql query.

let query = sql("SELECT resa_comment FROM reservation WHERE resa_id = ? ");

let query2 = query.bind::<Integer, _>(1286);

let result : Result<std::vec::Vec<String>, _> = query2.load(&connection);
dbg!(result);

But the result is

[src/bin/show_posts.rs:36] result = Err(
    DatabaseError(
        __Unknown,
        "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near \'?\' at line 1"
    )
)

The SQL query is correct because when I replace the "?" with a constant and remove the "bind", I get a correct result.

I know that I can map the table to a Rust structure but my goal is to pass complex requests with arguments so I was testing Rust and Diesel.

Is there something I missed ? Thanks.

Answer 1

The bind method does not replace question mark, it appends the value to the end of the query. So it should look like this:

let query = sql("SELECT resa_comment FROM reservation WHERE resa_id = ");
// ...

If you need to put value in the middle of the query, then you need to chain bind and sql calls, such as:

sql("SELECT resa_comment FROM reservation WHERE resa_id = ")
    .bind::<Integer, _>(1286)
    .sql(" AND something > ")
    .bind::<Integer, _>(1);

But note that you should avoid writing raw sql if it is not necessary.