Version: 2.0.x

Nested Selects

FromQueryResult and DerivePartialModel macros allows you to nest objects easily, simplifying the construction of complex queries.

Nested FromQueryResult

As a simple first example, we'd like to select Cake with Bakery:

#[derive(FromQueryResult)]
struct Cake {
    id: i32,
    name: String,
    #[sea_orm(nested)]
    bakery: Option<Bakery>,
}

#[derive(FromQueryResult)]
struct Bakery {
    #[sea_orm(alias = "bakery_id")]
    id: i32,
    #[sea_orm(alias = "bakery_name")]
    brand: String,
}

let cake: Cake = cake::Entity::find()
    .select_only()
    .column(cake::Column::Id)
    .column(cake::Column::Name)
    .column_as(bakery::Column::Id, "bakery_id")
    .column_as(bakery::Column::Name, "bakery_name")
    .left_join(bakery::Entity)
    .order_by_asc(cake::Column::Id)
    .into_model()
    .one(db)
    .await?
    .unwrap();

assert_eq!(
    cake,
    Cake {
        id: 1,
        name: "Basque cheesecake".to_string(),
        bakery: Some(Bakery {
            id: 20,
            brand: "Super Baker".to_string(),
        })
    }
);

Because the tables cake and bakery have some duplicate column names, we'd have to do custom selects. select_only here clears the default select list, and we apply aliases with column_as. Then, in FromQueryResult we use alias to map the query result back to the nested struct.

Nested Models

Since 2.0.0

#[derive(DerivePartialModel)]
#[sea_orm(entity = "cake::Entity", from_query_result)]
//                                 ^^^^^^^^^^^^^^^^^ no longer needed

DerivePartialModel allows you to omit the custom selects and aliases. The previous example can be written as:

#[derive(DerivePartialModel)]
#[sea_orm(entity = "cake::Entity")]
struct Cake {
    id: i32,
    name: String,
    #[sea_orm(nested)]
    bakery: Option<Bakery>,
}

#[derive(DerivePartialModel)]
#[sea_orm(entity = "bakery::Entity")]
struct Bakery {
    id: i32,
    #[sea_orm(from_col = "name")]
    brand: String,
}

// same as previous example, but without the custom selects
let cake: Cake = cake::Entity::find()
    .left_join(bakery::Entity)
    .order_by_asc(cake::Column::Id)
    .into_partial_model()
    .one(db)
    .await?
    .unwrap();

Under the hood, bakery_ prefix will be added to the column alias in the SQL query.

SELECT
    "cake"."id" AS "id",
    "cake"."name" AS "name",
    "bakery"."id" AS "bakery_id",
    "bakery"."name" AS "bakery_brand"
FROM "cake"
LEFT JOIN "bakery" ON "cake"."bakery_id" = "bakery"."id"
ORDER BY "cake"."id" ASC LIMIT 1

Regular Models can be nested!

Since 2.0.0

So the previous example can also be:

#[derive(DerivePartialModel)]
#[sea_orm(entity = "cake::Entity")]
struct Cake {
    id: i32,
    name: String,
    #[sea_orm(nested)]
    bakery: Option<bakery::Model>, // <- a regular full Model
}

Where all columns of the nested model are selected.

Use with Linked

Since 2.0.0

You can select partial model with Linked relation as well, however an alias matching the underlying query has to be applied. The following is equivalent to previous example.

pub struct ToBakery;
impl Linked for ToBakery {
    type FromEntity = super::cake::Entity;
    type ToEntity = super::bakery::Entity;

    fn link(&self) -> Vec<RelationDef> {
        vec![cake::Relation::Bakery.def()]
    }
}

#[derive(Debug, DerivePartialModel)]
#[sea_orm(entity = "cake::Entity")]
struct Cake {
    id: i32,
    name: String,
    #[sea_orm(nested, alias = "r0")] // <- apply alias
    bakery: Option<Bakery>,
}

let cake: Cake = cake::Entity::find()
    .left_join_linked(ToBakery)
    .order_by_asc(cake::Column::Id)
    .into_partial_model()
    .one(&ctx.db)
    .await?;
    .unwrap();

Join with alias

When the same table is joined more than once in the same query, it's necessary to use an alias. You can use the alias attribute to select columns from an alias.

#[derive(DerivePartialModel)]
#[sea_orm(entity = "cake::Entity")]
struct CakeFactory {
    id: i32,
    name: String,
    #[sea_orm(nested, alias = "factory")]
    bakery: Option<Factory>,
}

#[derive(DerivePartialModel)]
#[sea_orm(entity = "bakery::Entity")]
struct Factory {
    id: i32,
    #[sea_orm(from_col = "name")]
    plant: String,
}

let cake_factory: CakeFactory = cake::Entity::find()
    .join_as(
        JoinType::LeftJoin,
        cake::Relation::Bakery.def(),
        "factory",
    )
    .order_by_asc(cake::Column::Id)
    .into_partial_model()
    .one(db)
    .await?
    .unwrap();

Results in:

SELECT
    "cake"."id" AS "id",
    "cake"."name" AS "name",
    "factory"."id" AS "bakery_id",
    "factory"."name" AS "bakery_plant"
FROM "cake"
LEFT JOIN "bakery" AS "factory" ON "cake"."bakery_id" = "factory"."id"
ORDER BY "cake"."id" ASC LIMIT 1

Multiple Aliases

You can join the same Entity twice via two relations and have different aliases for each of them in the same query.

#[derive(DerivePartialModel)]
#[sea_orm(entity = "bakery::Entity")]
struct Bakery {
    name: String,
    #[sea_orm(nested, alias = "manager")]
    manager: Worker,
    #[sea_orm(nested, alias = "cashier")]
    cashier: Worker,
}

let bakery: Bakery = bakery::Entity::find()
    .join_as(
        sea_orm::JoinType::LeftJoin,
        bakery::Relation::Manager.def(),
        "manager",
    )
    .join_as(
        sea_orm::JoinType::LeftJoin,
        bakery::Relation::Cashier.def(),
        "cashier",
    )
    ..

Three-way Join

Our join plan starts from Order:

Order -> Customer
      -> LineItem -> Cake

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "order::Entity")]
struct Order {
    id: i32,
    total: Decimal,
    #[sea_orm(nested)]
    customer: Customer,
    #[sea_orm(nested)]
    line: LineItem,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "customer::Entity")]
struct Customer {
    name: String,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "lineitem::Entity")]
struct LineItem {
    price: Decimal,
    quantity: i32,
    #[sea_orm(nested)]
    cake: Cake,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "cake::Entity")]
struct Cake {
    name: String,
}

let items: Vec<Order> = order::Entity::find()
    .left_join(customer::Entity)
    .left_join(lineitem::Entity)
    .join(JoinType::LeftJoin, lineitem::Relation::Cake.def())
    .order_by_asc(order::Column::Id)
    .order_by_asc(lineitem::Column::Id)
    .into_partial_model()
    .all(db)
    .await?;

assert_eq!(
    items,
    [
        Order {
            id: 101,
            total: Decimal::from(10),
            customer: Customer {
                name: "Bob".to_owned()
            },
            line: LineItem {
                cake: Cake {
                    name: "Cheesecake".to_owned()
                },
                price: Decimal::from(2),
                quantity: 2,
            }
        },
        ..
    ]
);

Since Cake is a related Entity of LineItem, not Order, it does not satisfy the trait bound of left_join. It is thus necessary to use the more flexible join method.

Alternative shape

In the above, we make the nested structure resembles the topology of the join plan. But there is no restriction. Indeed, SQL flattens the select into a flat table, so as long as all columns can be found, we can freely arrange the result data structure.

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "order::Entity")]
struct OrderItem {
    #[sea_orm(nested)]
    order: Order,
    #[sea_orm(nested)]
    customer: Customer,
    #[sea_orm(nested)]
    line: LineItem,
    #[sea_orm(nested)]
    cake: Cake,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "order::Entity")]
struct Order {
    #[sea_orm(from_col = "id")]
    order_id: i32,
    total: Decimal,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "customer::Entity")]
struct Customer {
    name: String,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "lineitem::Entity")]
struct LineItem {
    price: Decimal,
    quantity: i32,
}

#[derive(Debug, DerivePartialModel, PartialEq)]
#[sea_orm(entity = "cake::Entity")]
struct Cake {
    name: String,
}

// the exact same select query
let items: Vec<Order> = order::Entity::find()
    .left_join(customer::Entity)
    .left_join(lineitem::Entity)
    .join(JoinType::LeftJoin, lineitem::Relation::Cake.def())
    .order_by_asc(order::Column::Id)
    .order_by_asc(lineitem::Column::Id)
    .into_partial_model()
    .all(db)
    .await?;

assert_eq!(
    items,
    [
        OrderItem {
            order: Order {
                order_id: 101,
                total: Decimal::from(10),
            },
            customer: Customer {
                name: "Bob".to_owned()
            },
            line: LineItem {
                price: Decimal::from(2),
                quantity: 2,
            },
            cake: Cake {
                name: "Cheesecake".to_owned()
            },
        },
        ..
    ]
);

Nested FromQueryResult​

Nested Models​

Regular Models can be nested!​

Use with Linked​

Join with alias​

Multiple Aliases​

Three-way Join​

Alternative shape​

Nested FromQueryResult

Nested Models

Regular Models can be nested!

Use with Linked

Join with alias

Multiple Aliases

Three-way Join

Alternative shape