Struct QueryScalar 

pub struct QueryScalar<T> { /* private fields */ }

A compiled single-column query. Created by the query_scalar! macro.

Returns values of a single column (e.g. COUNT(*), MAX(score), etc.). The type T must implement RowValue.

Example

let count: i64 = query_scalar!(i64, "SELECT COUNT(*) FROM users").fetch_one(&conn)?;
let names: Vec<String> = query_scalar!(String, "SELECT name FROM users").fetch_all(&conn)?;

Implementations

impl<T: RowValue> QueryScalar<T>

pub fn new(sql: &str, params: &[&dyn Debug]) -> Self

Construct a new QueryScalar. Called by the query_scalar! macro.

pub fn fetch_all(self, conn: &Connection) -> Result<Vec<T>>

Execute and return all scalar values as a Vec<T>.

Errors

Returns a hyperdb_api::Error on connection failure, SQL error, or type conversion failure.

pub fn fetch_one(self, conn: &Connection) -> Result<T>

Execute and return exactly one scalar value.

Errors

Returns Error::Conversion if the query returns zero rows.

pub fn fetch_optional(self, conn: &Connection) -> Result<Option<T>>

Execute and return Some(value) for the first row, or None.

Errors

Returns a hyperdb_api::Error on connection or SQL failure.

Trait Implementations

impl<T: Debug> Debug for QueryScalar<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.