Adding support for flatten attribute

[heroin-moose]

Hi guys,

I'm currently hacking up a flatten attribute similar to serde. The basic case is simple and works with a trivial patch, so this:

CREATE TABLE table1(id INTEGER PRIMARY KEY, a TEXT, b TEXT);

gets converted to this:

#[derive(FromRow)]
struct Foo {
    a: String,
    b: String
}

#[derive(FromRow)]
struct Bar {
    id: i64,
    #[sqlx(flatten)]
    foo: Foo
}

So far so good. However, I also want to support a little bit more complex scenarios, like this:

CREATE TABLE table1(id INTEGER, foo_id INTEGER);
CREATE TABLE table2(id INTEGER, name TEXT);

SELECT t1.*,
       t2.name AS foo_name
  FROM table1 AS t1,
       table2 AS t2
 WHERE t2.id = t1.foo_id;

#[derive(FromRow)]
struct Foo {
    id: i64,
    name: String
}

#[derive(FromRow)]
struct Bar {
    id: i64,
    #[sqlx(flatten_with_prefix = "foo_")]
    foo: Foo
}

I want all columns starting with "foo_" to be translated into Foo without the prefix. Of course, in this scenario the rename attribute can be added manually for each child structure field, but IMO the attribute parameter has two advantages:

1. Less typing of course
2. A single child struct can be used in multiple parent structs under different names

Unfortunately this requires passing the attribute parameter from the field level of the parent structure to the container level of the child structure. And this is a completely uncharted territory for me, because I haven't seen anyone doing this and I'm starting to think that maybe it's not possible at all. Maybe someone can share some thoughts?

[blagowtf]

Imho, supporting prefixes like this is essential for the flattened structs sql returns.

[chikko80]

yeah flatten is super painful at the moment

[chikko80]

@heroin-moose
any progress on this? Can i help with anything?

[heroin-moose]

Completely forgot about that... No, I've moved to diesel :(

[chikko80]

mhm i see..
Do you think its possible to do? Diesel looks to bloated for me

[heroin-moose]

It's possible to do, just requires some patience. Diesel actually requires far less dependencies.

[chikko80]

How does diesel solve this issue? @heroin-moose
I couldn't find any library which supports this feature, i don't understand how people actually efficiently code apis without such a important feature.

checkout this simple example:

pub struct Company {
    pub id: i32,
    pub name: String,
    pub street: String,
}

pub struct Manager {
    pub id: i32,
    pub name: String,
    pub street: String,    
    pub company_id: Option<i32>,

}

struct CompanyWithManager {
    company: Company,
    manager: Manager,
}

I just want to query and return the CompanyWithManager, therefore i just wanna join on the company_id and then build the CompanyWithManager struct from that db response. I know there is a way implementing FromRow (for sqlx) manually but it such a large amount of boilerplate.
I also coulnd't find a simple solution in https://github.com/SeaQL/sea-query

I'm just confused, how people do this in rust backends

[heroin-moose]

diesel-rs/diesel#1613