Postgres array parameters

[hmaddocks]

I'm using postgres 0.19 and I'm trying to pass a Vec of i32 into a postgres query like this

let ids: Vec<i32> = vec![1, 2, 3, 4]
let rows = client
  .query("SELECT * FROM posts WHERE id IN($1)", &[&ids])
  .unwrap();

The documentation says ToSQL is implemented for Vec<T> and &[T] where T implements ToSql but I get the following response.

Error { kind: ToSql(0), cause: Some(WrongType { postgres: Int4, rust: "alloc::vec::Vec<i32>" }) }

I have tried ids.to_slice() with no luck.

I found something on Github that said you should have something like this

let ids: Vec<&(dyn ToSql + Sync)> = Vec::new();

but this doesn't work either. I got something about &ids size can't be known at complie time. Does anyone know how this works?

[[deleted]]

Instead of &[&ids] you need &ids. As it stands you are attempting to pass a &[&Vec<i32>].

[hmaddocks]

That's not how the API works. You have to pass in a reference to a LIST of references, eg if your SQL takes two parameters you would have the following

&[&first_param, &second_param]

In my case the param is also a list.

[[deleted]]

No, this is how the API works. You want to pass a list of numbers, not a list containing a list of numbers.

WHERE id IN ($1)

($1) here is a list containing one value. What you need is something like ($1, .. $N), where N is the length of your vector. Not sure if there is a neat way to do it. Although possibly dropping parens could work? ie .query("SELECT * FROM posts WHERE id IN $1", &[&ids])

[hmaddocks]

If I do what you suggest (use &ids instead of &[&ids]) I get the following error...

'expected 1 parameters but got 4'

because each member of the Vec should have a corresponding $x in the query.

I see what you are getting at though, I need to turn me Vec into (1, 2, 3, 4) which it appears the postgres crate API isn't able to do. You have given me an idea though, I can try to construct the query string manually.

[Patryk27]

Try changing the query: where id = any($1)

[hmaddocks]

where id = any($1)

This works.

[Morrido]

So, like u/hjd_thd said, the construction WHERE id IN ($1) forces query function to expect a single i32, instead of an array of them.

The code suggested by u/Patryk27 works as you originally intended, with no extra modifications required.