issues-336 Array support

[ikrivosheev]

PR Info

• Closes Query binders: Add support for postgres arrays #336

This is continue: #390

[billy1624]

Hey @ikrivosheev, thanks for the draft!!

One question come up in my mind. For sea-query-binder and sea-query-driver, how do we bind the value on db driver? Because we can't figure out what's the type that implemented ValueTrait without the help of downcast and Any trait.

[billy1624]

@tyt2y3 ideas?

[ikrivosheev]

@billy1624 this is the biggest problem... Another idea is move sqlx and driver into sea-query

[ikrivosheev]

@Sytten ideas?

@billy1624 I can make two PR with with downcast and with move sqlx and driver into sea-query.

[billy1624]

The chain of pings loll

[ikrivosheev]

@tyt2y3 I think, I undestand!

[tyt2y3]

keeping the enum when you have the boxed trait

I wanted to pass-around primitives (and to some extend anything less than 16 bytes and impl Copy) on the stack, albeit they end up in a Values Vec.

[billy1624]

I imagine it's like

// Inside the root of sea-query

trait ValueTrait {}

enum SeaValue {
    I32(i32),
    Object(Box<dyn ValueTrait>),
}

impl ValueTrait for SeaValue {}

// Inside sea-orm-binder

struct SqlxMySqlValue<T>(T)
where
    T: ValueTrait + for<'q> Encode<'q, MySql>;

impl<'p, T> Encode<'p, MySql> for SqlxMySqlValue<T>
where
    T: ValueTrait + for<'q> Encode<'q, MySql>,
{
    fn encode_by_ref(
        &self,
        buf: &mut <MySql as sqlx::database::HasArguments<'_>>::ArgumentBuffer,
    ) -> sqlx::encode::IsNull {
        self.0.encode_by_ref(buf)
    }
}

[billy1624]

And, maybe...

trait ValueTrait {}

enum SeaValue {
    I32(i32),
    Object(Box<dyn ValueTrait>),
}

impl ValueTrait for SeaValue {}

impl<'p> Encode<'p, MySql> for dyn ValueTrait
where
    Self: for<'q> Encode<'q, MySql>,
{
    fn encode_by_ref(
        &self,
        buf: &mut <MySql as sqlx::database::HasArguments<'p>>::ArgumentBuffer,
    ) -> sqlx::encode::IsNull {
        self.encode_by_ref(buf)
    }
}

[ikrivosheev]

@billy1624 it seems like it won't work...

// Inside the root of sea-query

trait ValueTrait {}

enum Value {
    I32(i32),
    Object(Box<dyn ValueTrait>),
}

impl ValueTrait for Value {}

// Inside sea-query-rusqlite

#[derive(Clone, Debug)]
struct RusqliteValue<T>(T)
where
    T: ValueTrait + ToSql;

impl<T> ToSql for RusqliteValue<T>
where
    T: ValueTrait + ToSql,
{
    fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
        self.0.to_sql()
    }
}

#[derive(Clone, Debug)]
pub struct RusqliteValues<T>(pub Vec<RusqliteValue<T>>);  // <--- I cannot put here enum Value because it does not impl ToSql and I cannot make this parameter generic and I cannot impl ToSql for Value because it from other trait

[tyt2y3]

Perhaps we can start from removing the object variants from Value (while keeping the primitive variants)?

[billy1624]

The requirements:

1. No downcast
2. Keep SeaQuery clean, outsource heavy lifting of value binding to binder
3. Include binder in sea-query's dependency but do not turn on the features by default
4. It could be Value in sea-query, ValueTrait in binder
5. Could we enable multiple backend support in an additive compatible way? I.e. if one downstream turned on SQLx and another turn on postgres. The ? cargo syntax should be helpful

[ikrivosheev]

@billy1624 @tyt2y3 , hello! I have a bad surprise. trait ToSql from postgres-types crate need: Self: Sized, but I cannot make ValueTrait: Sized, because I need dyn ValueTrait

[ikrivosheev]

It looks like instead of create our own ValueTrait make all types, which hold Value should be generic...

[ikrivosheev]

Hmmm another sought... Black magic with unsafe. This should work. I can store row pointer to data and then transmute it to value and type get from enum.

Example: https://github.com/Diggsey/ijson/

[tyt2y3]

May be we should postpone ValueTrait to after 0.27, and trying to get array working with sqlx-postgres for now

[ikrivosheev]

Ah, one more problem... I try something like this:

pub trait Sqlx<'q, T: Database>: Encode<'q, T> + Type<T> {}

pub trait ValueTrait
where
    Self: Debug,
{
    fn to_sql_string(&self) -> String;

    #[cfg(feature = "with-postgres")]
    fn as_postgres_to_sql(&self) -> &(dyn PostgresToSql + Sync + Send);

    #[cfg(feature = "sqlx-mysql")]
    fn as_sqlx_mysql<'q>(&'q self) -> &(dyn Sqlx<'q, MySql>);

    #[cfg(feature = "sqlx-postgres")]
    fn as_sqlx_postgres<'q>(&'q self) -> &(dyn Sqlx<'q, Postgres>);

    #[cfg(feature = "sqlx-sqlite")]
    fn as_sqlx_sqlite<'q>(&'q self) -> &(dyn Sqlx<'q, Sqlite>);
}

#[derive(Debug, Clone)]
pub enum Value {
    Bool(bool),
    TinyInt(i8),
    SmallInt(i16),
    Int(i32),
    BigInt(i64),
    TinyUnsigned(u8),
    SmallUnsigned(u16),
    Unsigned(u32),
    BigUnsigned(u64),
    Float(f32),
    Double(f64),
    #[cfg(feature = "thread-safe")]
    Object(SeaRc<Box<dyn ValueTrait + Sync + Send>>),
    #[cfg(not(feature = "thread-safe"))]
    Object(SeaRc<Box<dyn ValueTrait>>),
}

impl ValueTrait for Value {...}

Problems:

1. I cannot combine rusqlite and sqlx in one crate (failed to select a version for libsqlite3-sys)
2. I cannot make &dyn Sqlx because Type<T> - Sqlx cannot be made into an object` - Make sqlx::Type object safe by taking &self launchbadge/sqlx#1461
3. sea-query-postgres throw compile error: the to_sql method cannot be invoked on a trait object`

[tyt2y3]

1: I think we won't combine them
2: we have to create our own trait based on that but is object safe

[billy1624]

I guess we can close this?

[ikrivosheev]

I guess we can close this?

@billy1624 I think, no, we cannot... I will continue work on it.

[billy1624]

Alright, a trait based Value with array support would be cool. And a huge step forward :)