DuckStruct Derive

#[derive(DuckStruct)]: map a Rust named-field struct to a DuckDB STRUCT value, with field renaming and optional Diesel emission.

Requires feature = "derive". See the derives overview for the shared #[duck(...)] attributes and rename_all casings.

#[derive(DuckStruct)] maps a Rust named-field struct to a DuckDB STRUCT value (named fields, fixed schema). It generates From<T> for DuckValue and FromDuckValue for T, so the struct converts to and from a DuckValue::Struct.

use better_duck_core::DuckStruct;

#[derive(DuckStruct, Debug, PartialEq)]
#[duck(rename_all = "camelCase")]
struct Point {
    x_coord: i32,
    y_coord: i32,
    #[duck(rename = "z")]
    depth: Option<i32>,
}
// Maps to STRUCT(xCoord INTEGER, yCoord INTEGER, z INTEGER)

It shares the same #[duck(rename = "…")] / #[duck(rename_all = "…")] / #[duck(crate = …)] attributes as #[derive(FromRow)], with the same resolution order.

DuckStruct maps to a DuckDB STRUCT value (a column value), whereas FromRow maps a whole query row. Reach for DuckStruct when a single column is itself a STRUCT; reach for FromRow to read a result set’s rows.

Diesel emission

With better-duck-diesel’s derive feature on, #[derive(DuckStruct)] additionally emits Diesel ToSql / FromSql against better_duck_diesel::sql_types::DuckStruct (via sql_query + QueryableByName, routing through the DuckDb backend), so the same type binds and loads through a DuckDbConnection. The deriving crate must then depend on better-duck-diesel — see the Diesel docs. Nothing extra is emitted with the feature off.

See also

• DuckEnum derive · FromRow / ToRow.
• Composite types — the runtime DuckStruct value.
• Derives overview — the rename_all casings table.