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column.rs
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column.rs
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use crate::database::Database;
use crate::error::Error;
use std::fmt::Debug;
pub trait Column: 'static + Send + Sync + Debug {
type Database: Database;
/// Gets the column ordinal.
///
/// This can be used to unambiguously refer to this column within a row in case more than
/// one column have the same name
fn ordinal(&self) -> usize;
/// Gets the column name or alias.
///
/// The column name is unreliable (and can change between database minor versions) if this
/// column is an expression that has not been aliased.
fn name(&self) -> &str;
/// Gets the type information for the column.
fn type_info(&self) -> &<Self::Database as Database>::TypeInfo;
}
/// A type that can be used to index into a [`Row`] or [`Statement`].
///
/// The [`get`] and [`try_get`] methods of [`Row`] accept any type that implements `ColumnIndex`.
/// This trait is implemented for strings which are used to look up a column by name, and for
/// `usize` which is used as a positional index into the row.
///
/// [`Row`]: crate::row::Row
/// [`Statement`]: crate::statement::Statement
/// [`get`]: crate::row::Row::get
/// [`try_get`]: crate::row::Row::try_get
///
pub trait ColumnIndex<T: ?Sized>: Debug {
/// Returns a valid positional index into the row or statement, [`ColumnIndexOutOfBounds`], or,
/// [`ColumnNotFound`].
///
/// [`ColumnNotFound`]: Error::ColumnNotFound
/// [`ColumnIndexOutOfBounds`]: Error::ColumnIndexOutOfBounds
fn index(&self, container: &T) -> Result<usize, Error>;
}
impl<T: ?Sized, I: ColumnIndex<T> + ?Sized> ColumnIndex<T> for &'_ I {
#[inline]
fn index(&self, row: &T) -> Result<usize, Error> {
(**self).index(row)
}
}
#[macro_export]
macro_rules! impl_column_index_for_row {
($R:ident) => {
impl $crate::column::ColumnIndex<$R> for usize {
fn index(&self, row: &$R) -> Result<usize, $crate::error::Error> {
let len = $crate::row::Row::len(row);
if *self >= len {
return Err($crate::error::Error::ColumnIndexOutOfBounds { len, index: *self });
}
Ok(*self)
}
}
};
}
#[macro_export]
macro_rules! impl_column_index_for_statement {
($S:ident) => {
impl $crate::column::ColumnIndex<$S<'_>> for usize {
fn index(&self, statement: &$S<'_>) -> Result<usize, $crate::error::Error> {
let len = $crate::statement::Statement::columns(statement).len();
if *self >= len {
return Err($crate::error::Error::ColumnIndexOutOfBounds { len, index: *self });
}
Ok(*self)
}
}
};
}