Represent several relations between same types

src/entity/column.rs

@@ -1,6 +1,6 @@
-use std::str::FromStr;
 use crate::{EntityName, IdenStatic, Iterable};
 use sea_query::{DynIden, Expr, SeaRc, SelectStatement, SimpleExpr, Value};
+use std::str::FromStr;
 
 #[derive(Debug, Clone)]
 pub struct ColumnDef {

src/entity/model.rs

@@ -1,4 +1,4 @@
-use crate::{DbErr, EntityTrait, QueryFilter, QueryResult, Related, Select};
+use crate::{DbErr, EntityTrait, Linked, QueryFilter, QueryResult, Related, Select};
 pub use sea_query::Value;
 use std::fmt::Debug;
 
@@ -16,6 +16,13 @@ pub trait ModelTrait: Clone + Debug {
     {
         <Self::Entity as Related<R>>::find_related().belongs_to(self)
     }
+
+    fn find_linked<L>(&self, l: L) -> Select<L::ToEntity>
+    where
+        L: Linked<FromEntity = Self::Entity>,
+    {
+        l.find_linked()
+    }
 }
 
 pub trait FromQueryResult {

src/entity/prelude.rs

@@ -1,9 +1,9 @@
 pub use crate::{
     error::*, ActiveModelBehavior, ActiveModelTrait, ColumnDef, ColumnTrait, ColumnType,
     DeriveActiveModel, DeriveActiveModelBehavior, DeriveColumn, DeriveCustomColumn, DeriveEntity,
-    DeriveModel, DerivePrimaryKey, EntityName, EntityTrait, EnumIter, Iden, IdenStatic, ModelTrait,
-    PrimaryKeyToColumn, PrimaryKeyTrait, QueryFilter, QueryResult, Related, RelationDef,
-    RelationTrait, Select, Value,
+    DeriveModel, DerivePrimaryKey, EntityName, EntityTrait, EnumIter, Iden, IdenStatic, Linked,
+    ModelTrait, PrimaryKeyToColumn, PrimaryKeyTrait, QueryFilter, QueryResult, Related,
+    RelationDef, RelationTrait, Select, Value,
 };
 
 #[cfg(feature = "with-json")]

src/entity/relation.rs

@@ -28,6 +28,22 @@ where
     }
 }
 
+pub trait Linked {
+    type FromEntity: EntityTrait;
+
+    type ToEntity: EntityTrait;
+
+    fn link(&self) -> Vec<RelationDef>;
+
+    fn find_linked(&self) -> Select<Self::ToEntity> {
+        let mut select = Select::new();
+        for rel in self.link().into_iter().rev() {
+            select = select.join_rev(JoinType::InnerJoin, rel);
+        }
+        select
+    }
+}
+
 pub struct RelationDef {
     pub rel_type: RelationType,
     pub from_tbl: TableRef,

src/executor/select.rs

@@ -128,7 +128,7 @@ where
     E: EntityTrait,
     F: EntityTrait,
 {
-    fn into_model<M, N>(self) -> Selector<SelectTwoModel<M, N>>
+    pub fn into_model<M, N>(self) -> Selector<SelectTwoModel<M, N>>
     where
         M: FromQueryResult,
         N: FromQueryResult,

src/query/helper.rs

@@ -3,7 +3,7 @@ use crate::{
     RelationDef,
 };
 use sea_query::{
-    Alias, Expr, IntoCondition, SeaRc, SelectExpr, SelectStatement, SimpleExpr, TableRef,
+    Alias, Expr, Iden, IntoCondition, SeaRc, SelectExpr, SelectStatement, SimpleExpr, TableRef,
 };
 pub use sea_query::{Condition, ConditionalStatement, DynIden, JoinType, Order, OrderedStatement};
 
@@ -66,6 +66,33 @@ pub trait QuerySelect: Sized {
         self
     }
 
+    /// Add a select column with prefixed alias
+    /// ```
+    /// use sea_orm::{entity::*, query::*, tests_cfg::cake, DbBackend};
+    ///
+    /// assert_eq!(
+    ///     cake::Entity::find()
+    ///         .select_only()
+    ///         .column_as_prefixed(cake::Column::Id.count(), "A_", cake::Column::Id)
+    ///         .build(DbBackend::Postgres)
+    ///         .to_string(),
+    ///     r#"SELECT COUNT("cake"."id") AS "A_id" FROM "cake""#
+    /// );
+    /// ```
+    fn column_as_prefixed<C, I>(mut self, col: C, prefix: &str, alias: I) -> Self
+    where
+        C: IntoSimpleExpr,
+        I: Iden,
+    {
+        self.query().expr(SelectExpr {
+            expr: col.into_simple_expr(),
+            alias: Some(SeaRc::new(Alias::new(
+                vec![prefix, alias.to_string().as_str()].join("").as_str(),
+            ))),
+        });
+        self
+    }
+
     /// Add a group by column
     /// ```
     /// use sea_orm::{entity::*, query::*, tests_cfg::cake, DbBackend};

src/query/join.rs

@@ -1,4 +1,4 @@
-use crate::{EntityTrait, QuerySelect, Related, Select, SelectTwo, SelectTwoMany};
+use crate::{EntityTrait, Linked, QuerySelect, Related, Select, SelectTwo, SelectTwoMany};
 pub use sea_query::JoinType;
 
 impl<E> Select<E>
@@ -57,6 +57,19 @@ where
     {
         self.left_join(r).select_with(r)
     }
+
+    /// Left Join with a Linked Entity and select both Entity.
+    pub fn find_also_linked<L, T>(self, l: L) -> SelectTwo<E, T>
+    where
+        L: Linked<FromEntity = E, ToEntity = T>,
+        T: EntityTrait,
+    {
+        let mut slf = self;
+        for rel in l.link() {
+            slf = slf.join(JoinType::LeftJoin, rel);
+        }
+        slf.select_also(T::default())
+    }
 }
 
 #[cfg(test)]
@@ -220,4 +233,44 @@ mod tests {
             .join(" ")
         );
     }
+
+    #[test]
+    fn join_10() {
+        let cake_model = cake::Model {
+            id: 12,
+            name: "".to_owned(),
+        };
+
+        assert_eq!(
+            cake_model
+                .find_linked(cake::CakeToFilling)
+                .build(DbBackend::MySql)
+                .to_string(),
+            [
+                r#"SELECT `filling`.`id`, `filling`.`name`"#,
+                r#"FROM `filling`"#,
+                r#"INNER JOIN `cake_filling` ON `cake_filling`.`filling_id` = `filling`.`id`"#,
+                r#"INNER JOIN `cake` ON `cake`.`id` = `cake_filling`.`cake_id`"#,
+            ]
+            .join(" ")
+        );
+    }
+
+    #[test]
+    fn join_11() {
+        assert_eq!(
+            cake::Entity::find()
+                .find_also_linked(cake::CakeToFilling)
+                .build(DbBackend::MySql)
+                .to_string(),
+            [
+                r#"SELECT `cake`.`id` AS `A_id`, `cake`.`name` AS `A_name`,"#,
+                r#"`filling`.`id` AS `B_id`, `filling`.`name` AS `B_name`"#,
+                r#"FROM `cake`"#,
+                r#"LEFT JOIN `cake_filling` ON `cake`.`id` = `cake_filling`.`cake_id`"#,
+                r#"LEFT JOIN `filling` ON `cake_filling`.`filling_id` = `filling`.`id`"#,
+            ]
+            .join(" ")
+        );
+    }
 }

src/tests_cfg/cake.rs

@@ -73,4 +73,19 @@ impl Related<super::filling::Entity> for Entity {
     }
 }
 
+pub struct CakeToFilling;
+
+impl Linked for CakeToFilling {
+    type FromEntity = Entity;
+
+    type ToEntity = super::filling::Entity;
+
+    fn link(&self) -> Vec<RelationDef> {
+        vec![
+            super::cake_filling::Relation::Cake.def().rev(),
+            super::cake_filling::Relation::Filling.def(),
+        ]
+    }
+}
+
 impl ActiveModelBehavior for ActiveModel {}

tests/common/bakery_chain/baker.rs

@@ -81,4 +81,22 @@ impl Related<super::cake::Entity> for Entity {
     }
 }
 
+pub struct BakedForCustomer;
+
+impl Linked for BakedForCustomer {
+    type FromEntity = Entity;
+
+    type ToEntity = super::customer::Entity;
+
+    fn link(&self) -> Vec<RelationDef> {
+        vec![
+            super::cakes_bakers::Relation::Baker.def().rev(),
+            super::cakes_bakers::Relation::Cake.def(),
+            super::lineitem::Relation::Cake.def().rev(),
+            super::lineitem::Relation::Order.def(),
+            super::order::Relation::Customer.def(),
+        ]
+    }
+}
+
 impl ActiveModelBehavior for ActiveModel {}