Struct MaybeTable 

pub struct MaybeTable<'scope, T> { /* private fields */ }

A table which contains a tag indicating whether a query returned rows. Use Query::optional to construct this.

Implementations

impl<'scope, T: Table<'scope>> MaybeTable<'scope, T>

pub fn project<U, F>(&self, f: F) -> Expr<'scope, Option<U>>

where F: FnOnce(&T) -> Expr<'_, U>,

Project out an expression from the maybe table

pub fn maybe<U: Table<'scope>, F>(self, fallback: U, f: F) -> U

where F: FnOnce(T) -> U,

Test if the table is None, if it is, use the fallback, otherwise call f.

Trait Implementations

impl<'scope, T: ForLifetimeTable + Table<'scope>> ForLifetimeTable for MaybeTable<'scope, T>

where for<'lt> T::WithLt<'lt>: Table<'lt>,

type WithLt<'lt> = MaybeTable<'lt, <T as ForLifetimeTable>::WithLt<'lt>>

Substitute the lifetime of this table with 'lt.

fn with_lt<'lt>(self, marker: &mut WithLtMarker) -> Self::WithLt<'lt>

Coerce the lifetime of this table. This is used internally by the library.

impl<'scope, T: ShortenLifetime> ShortenLifetime for MaybeTable<'scope, T>

type Shortened<'small> = MaybeTable<'small, <T as ShortenLifetime>::Shortened<'small>> where Self: 'small

fn shorten_lifetime<'small, 'large: 'small>(self) -> Self::Shortened<'small>

where Self: 'large,

Shorten a lifetime, normally rust does this automatically, but if the lifetime is invariant due to being used in a Gat or trait, we need to do it manually.

impl<'scope, T: Table<'scope>> Table<'scope> for MaybeTable<'scope, T>

type Result = Option<<T as Table<'scope>>::Result>

The value a row of this table has when loaded from the database.

fn visit(&self, f: &mut impl FnMut(&ErasedExpr), mode: VisitTableMode)

Visit each expr in the table.

fn visit_mut( &mut self, f: &mut impl FnMut(&mut ErasedExpr), mode: VisitTableMode, )

Visit each expr in the table, with a mutable reference.

impl<T: TableLoaderSqlx> TableLoaderSqlx for MaybeTable<'static, T>

Available on crate feature sqlx only.

fn load<'a>( &self, values: &mut impl Iterator<Item = PgValueRef<'a>>, ) -> Self::Result

Load the table given an iterator over a row’s values

fn skip<'a>(&self, values: &mut impl Iterator<Item = PgValueRef<'a>>)

discard N columns from the iterator ofer a row This is used when this value was discarded by a MaybeTable.