Struct Assignments 

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

A SET list that is known non-empty, which is the only kind that has a SQL form. Every *Update derives Default, and that value — what a PATCH handler holds when the request changed nothing — has no assignments at all, so the check belongs where such a value enters a statement rather than at rendering time.

Implementations

impl<T: Table> Assignments<T>

pub fn set_to<C, V, Idxs>(_column: Column<C>, value: V) -> Self

where C: ColumnKey<Table = T> + Writable, V: IntoExpr, V::Sql: AssignsTo<C::Sql>, WrittenTable<T>: Superset<V::Req, Idxs>,

column = <expression> — the assignments a value can’t say: updated_at = now(), version = version + 1. The expression is checked against the table being written to, exactly as a WHERE condition is.

pub fn and_set_to<C, V, Idxs>(self, _column: Column<C>, value: V) -> Self

where C: ColumnKey<Table = T> + Writable, V: IntoExpr, V::Sql: AssignsTo<C::Sql>, WrittenTable<T>: Superset<V::Req, Idxs>,

One more of them, so a statement can assign several expressions.

impl<T> Assignments<T>

pub fn from_row<R: UpdateRow<Table = T>>(row: R) -> Result<Self, NothingToSet>

The SET list a request struct describes — the one fallible step in building a statement, since a *Update whose every field is untouched describes no assignment. Mixed with computed ones as Assignments::from_row(patch)?.and_set_to(col, expr).

Trait Implementations

impl<T> Clone for Assignments<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Debug for Assignments<T>

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

Formats the value using the given formatter.