Struct Relation 

pub struct Relation<P, C> { /* private fields */ }

Describes how a parent model P relates to a related model C.

Built by the accessors #[relations] generates, such as User::posts().

Implementations

impl<P, C> Relation<P, C>

pub fn has_many( parent_table: &'static str, parent_key: &'static str, child_table: &'static str, child_key: &'static str, ) -> Self

Builds a has_many relation: parent.parent_key = child.child_key.

pub fn belongs_to( local_table: &'static str, local_key: &'static str, parent_table: &'static str, parent_key: &'static str, ) -> Self

Builds a belongs_to relation: local.local_key = parent.parent_key.

pub fn filter(self, predicate: Expr) -> Self

Constrains the related rows loaded by preload.

Has no effect on a plain join.

pub fn order_by(self, term: OrderTerm) -> Self

Orders the related rows loaded by preload.

pub fn limit(self, limit: u64) -> Self

Caps the number of related rows loaded by preload for each parent. Useful when a single parent has a high-cardinality child table (for example a popular user with thousands of posts) and pulling every row would exhaust memory.

pub fn kind(&self) -> RelationKind

Returns the kind of this relation.

pub fn target_table(&self) -> &'static str

Returns the table this relation brings into a query when joined.

pub fn from_column(&self) -> &'static str

Returns the owning side column of the join condition.

pub fn to_column(&self) -> &'static str

Returns the related side column of the join condition.

pub fn preload_filters(&self) -> &[Expr]

Returns the extra predicates applied when preloading.

pub fn preload_order_by(&self) -> &[OrderTerm]

Returns the ordering applied when preloading.

pub fn preload_limit(&self) -> Option<u64>

Returns the per-parent row cap applied when preloading, if any.

pub fn join_node(&self) -> Join

Builds an inner join node for this relation.

pub fn join_node_with_kind(&self, kind: JoinKind) -> Join

Builds a join node with the given kind.