Insert shapes with #[derive(New)]

When you create a row, some fields are the ORM's job, not yours: an autoincrement primary key, auto_now_add / auto_now timestamps, auto_uuid public ids, auto_user* stamps, and relations that own no column (M2M, ReverseSet, OneToOne). Constructing a full model literal just to insert one forces you to name all of them anyway (id: 0, created_at: Default::default(), …).

#[derive(New)] generates a companion insert shape — <Model>New — that omits exactly those fields, so you name only the data you actually supply. It's the type-level version of Django's Model.objects.create(name=…).

One example

use umbral::prelude::*;
use chrono::{DateTime, Utc};
 
#[derive(Debug, Clone, sqlx::FromRow, serde::Serialize, serde::Deserialize, Model, New)]
#[umbral(table = "widget")]
pub struct Widget {
    pub id: i64,                       // autoincrement — omitted from WidgetNew
    #[umbral(string)]
    pub name: String,                  // yours — kept
    #[umbral(auto_now_add)]
    pub created_at: DateTime<Utc>,     // stamped on insert — omitted
    #[umbral(auto_now)]
    pub updated_at: DateTime<Utc>,     // stamped on write — omitted
}
 
// Name only what you supply — no id, no timestamps.
let w = Widget::objects()
    .create(WidgetNew { name: "gizmo".into() })
    .await?;
assert!(w.id > 0);                     // PK assigned, timestamps stamped

create, get_or_create, and update_or_create all take impl Into<T>, so a <Model>New works everywhere a full model does — and, because T: Into<T> is identity, passing a full model still works unchanged:

// get_or_create / update_or_create accept the insert shape as `defaults`:
let (w, created) = Widget::objects()
    .get_or_create(widget::NAME.eq("gizmo"), WidgetNew { name: "gizmo".into() })
    .await?;

What's kept vs. omitted

The generated From<<Model>New> for <Model> fills the omitted fields with Default::default(); the typed write path then overwrites the PK sentinel and every auto column on insert, so the row is correct. See also Reusable model bases for the ..Default::default() construction shortcut on based models.