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Version: 0.6.x 🚧

One to Many

A one-to-many relation is similar to a one-to-one relation. In the previous section, we gave the example of "a Cake entity has at most one Fruit topping". To make it a one-to-many relation, we remove the "at most one" constraint. So, we have a Cake entity that might have many Fruit toppings.

Defining the Relation

This is almost identical to defining a one-to-one relation; the only difference is that we use Entity::has_many() method here.

entity/cake.rs
#[derive(Copy, Clone, Debug, EnumIter)]
pub enum Relation {
Fruit,
}

impl RelationTrait for Relation {
fn def(&self) -> RelationDef {
match self {
Self::Fruit => Entity::has_many(super::fruit::Entity).into(),
}
}
}

impl Related<super::fruit::Entity> for Entity {
fn to() -> RelationDef {
Relation::Fruit.def()
}
}

Alternatively, the definition can be shortened by the DeriveRelation macro, where the following is equivalent to the above:

#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
pub enum Relation {
#[sea_orm(has_many = "super::fruit::Entity")]
Fruit,
}

Defining the Inverse Relation

It is the same as defining the one-to-one inverse relation.

entity/fruit.rs
#[derive(Copy, Clone, Debug, EnumIter)]
pub enum Relation {
Cake,
}

impl RelationTrait for Relation {
fn def(&self) -> RelationDef {
match self {
Self::Cake => Entity::belongs_to(super::cake::Entity)
.from(Column::CakeId)
.to(super::cake::Column::Id)
.into(),
}
}
}

impl Related<super::cake::Entity> for Entity {
fn to() -> RelationDef {
Relation::Cake.def()
}
}

Alternatively, the definition can be shortened by the DeriveRelation macro, where the following is equivalent to the above:

#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
pub enum Relation {
#[sea_orm(
belongs_to = "super::cake::Entity",
from = "Column::CakeId",
to = "super::cake::Column::Id"
)]
Cake,
}