Support adding expressions for ON CONFLICT targets

[sumeetattree]

PR Info

Supports adding expressions to ON CONFLICT targets on supported databases (postgres, and sqlite);

INSERT ... ON CONFLICT ("id", LOWER("email")) DO UPDATE SET "name" = "excluded"."name"

• Closes OnConflict does not support adding a function expression to list of columns #678

New Features

• Added an OnConflict::expr() and OnConflict::exprs() impls to support adding custom expressions to on_conflict targets

Breaking Changes

None

Changes

None

[sumeetattree]

There is little weirdness in how OnConflict struct is initialized:

let conflict_column = OnConflict::column(Glyph::Id).to_owned(); // no need to call `new` first

let conflict_expr = OnConflict::new().expr(Func::lower(Expr::col(Glyph::Tokens))).to_owned();

.column() method acts like a constructor but .expr() requires the object to be already constructed. Changing .expr() method to also act like a constructor locks us out of using both columns and expressions in the same ON CONFLICT clause.

impl OnConflict {
    pub fn column(col) -> Self {
        // ...
    }

    pub fn expr(expr) -> Self {
        // ...
    }
}
let conflict = OnConflict::column(Glyph::Id)
    .expr(Func::lower(Expr::col(Glyph::Tokens)))  // will NOT work!
    .to_string();

On the flip side, using .expr() alone is a little cumbersome because we must first call .new().

However, doing this:

impl OnConflict {
    pub fn column(&mut self, col) -> &mut Self {
        // ...
    }

    pub fn expr(&mut self, expr) -> &mut Self {
        // ...
    }
}

is a breaking change for all .column() and .columns() consumers.

How do we reconcile these api differences?

[sumeetattree]

@ikrivosheev I have tried fixing the formatting issues raised by the workflow. I think it's sorted. Can you take another look?

[tyt2y3]

Sorry for the delay

[github-actions]

🎉 Released In 0.30.5 🎉

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