Update

Update DuckDB rows through Diesel: diesel::update with a filtered target, setting single or multiple columns, updating from an AsChangeset struct, and returning changed values.

Modifying rows with diesel::update. Portable Diesel on the DuckDB backend.

Updating columns

diesel::update(target).set(...) where target is a filtered table. Set one column, or a tuple of columns:

use diesel::prelude::*;

// single column
diesel::update(products::table.filter(products::id.eq(1)))
    .set(products::price.eq(11.99))
    .execute(&mut conn)?;

// several columns
diesel::update(products::table.filter(products::id.eq(1)))
    .set((products::name.eq("widget-mk2"), products::price.eq(12.5)))
    .execute(&mut conn)?;

.execute returns the number of rows changed.

diesel::update(products::table) with no .filter updates every row. Always scope the target with .filter(...) unless a table-wide update is truly intended.

Expressions in SET

The right-hand side can reference columns and DuckDB scalar functions, not just literals:

use better_duck_diesel::dsl::*;

diesel::update(products::table.filter(products::id.eq(1)))
    .set(products::name.eq(upper(products::name)))  // UPDATE … SET name = upper(name)
    .execute(&mut conn)?;

See the DSL overview for the function library.

Updating from a struct

A #[derive(AsChangeset)] struct turns into the SET clause. Option fields that are None are omitted from the clause — a convenient partial-update pattern:

#[derive(AsChangeset)]
#[diesel(table_name = products)]
struct ProductPatch<'a> {
    name: Option<&'a str>,   // None -> not touched
    price: Option<f64>,
}

diesel::update(products::table.filter(products::id.eq(1)))
    .set(&ProductPatch { name: None, price: Some(19.99) })  // only price is updated
    .execute(&mut conn)?;

See Schema for deriving AsChangeset.

To treat a None as “set this column to NULL” rather than “leave it alone”, add #[diesel(treat_none_as_null = true)] to the AsChangeset struct — this is Diesel’s own attribute.

Returning updated values

Chain .returning(...) with get_result/get_results to read columns back after the update:

let new_price: f64 = diesel::update(products::table.filter(products::id.eq(1)))
    .set(products::price.eq(11.99))
    .returning(products::price)
    .get_result(&mut conn)?;

See RETURNING.

See also

Delete

Remove rows.

Upsert

Insert-or-update in one statement.

RETURNING

Read values back from an update.

DSL overview

Functions usable in a SET expression.