rustyroad 1.7.1

Rusty Road is a framework written in Rust that is based on Ruby on Rails. It is designed to provide the familiar conventions and ease of use of Ruby on Rails, while also taking advantage of the performance and efficiency of Rust.
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//! Column duplication: create a shadow physical column beside the original.
//!
//! An in-flight change writes to a shadow column rather than mutating the original,
//! so readers of the old schema version keep seeing the original values. The two are
//! kept in sync by triggers until the migration completes.

mod promote;

use super::super::naming::temporary_name;
use super::super::quote::quote_ident;

/// A column to duplicate, and the shape the copy should take.
pub struct Duplicate<'a> {
    pub table: &'a str,
    pub column: &'a str,
    /// Type of the shadow column; defaults to text when unknown.
    pub column_type: Option<&'a str>,
    pub nullable: bool,
    pub default: Option<&'a str>,
}

impl Duplicate<'_> {
    /// Returns the physical name of the shadow column.
    pub fn shadow_name(&self) -> String {
        temporary_name(self.column)
    }

    /// Returns the statement adding the shadow column.
    ///
    /// The shadow is always created nullable: existing rows have no value yet, and a
    /// NOT NULL constraint would fail before the backfill has run. The constraint is
    /// applied at completion instead.
    pub fn add_column(&self) -> String {
        let mut sql = format!(
            "ALTER TABLE {} ADD COLUMN IF NOT EXISTS {} {}",
            quote_ident(self.table),
            quote_ident(&self.shadow_name()),
            self.column_type.unwrap_or("text")
        );

        if let Some(default) = self.default {
            sql.push_str(&format!(" DEFAULT {default}"));
        }

        sql
    }
}