Many to many by reverse relation

examples/sqlx-mysql/src/example_cake.rs

@@ -24,7 +24,6 @@ pub enum PrimaryKey {
 #[derive(Copy, Clone, Debug, EnumIter)]
 pub enum Relation {
     Fruit,
-    CakeFilling,
 }
 
 impl ColumnTrait for Column {
@@ -45,10 +44,6 @@ impl RelationTrait for Relation {
                 .from(Column::Id)
                 .to(super::fruit::Column::CakeId)
                 .into(),
-            Self::CakeFilling => Entity::has_many(super::cake_filling::Entity)
-                .from(Column::Id)
-                .to(super::cake_filling::Column::CakeId)
-                .into(),
         }
     }
 }
@@ -65,7 +60,7 @@ impl Related<super::filling::Entity> for Entity {
     }
 
     fn via() -> Option<RelationDef> {
-        Some(Relation::CakeFilling.def())
+        Some(super::cake_filling::Relation::Cake.def().rev())
     }
 }
 
@@ -73,4 +68,8 @@ impl Model {
     pub fn find_fruit(&self) -> Select<super::fruit::Entity> {
         Entity::find_related().belongs_to::<Entity>(self)
     }
+
+    pub fn find_filling(&self) -> Select<super::filling::Entity> {
+        Entity::find_related().belongs_to::<Entity>(self)
+    }
 }

examples/sqlx-mysql/src/example_cake_filling.rs

@@ -42,11 +42,11 @@ impl ColumnTrait for Column {
 impl RelationTrait for Relation {
     fn def(&self) -> RelationDef {
         match self {
-            Self::Cake => Entity::has_many(super::cake::Entity)
+            Self::Cake => Entity::has_one(super::cake::Entity)
                 .from(Column::CakeId)
                 .to(super::cake::Column::Id)
                 .into(),
-            Self::Filling => Entity::has_many(super::filling::Entity)
+            Self::Filling => Entity::has_one(super::filling::Entity)
                 .from(Column::FillingId)
                 .to(super::filling::Column::Id)
                 .into(),

examples/sqlx-mysql/src/example_filling.rs

@@ -40,3 +40,19 @@ impl RelationTrait for Relation {
         panic!()
     }
 }
+
+impl Related<super::cake::Entity> for Entity {
+    fn to() -> RelationDef {
+        super::cake_filling::Relation::Cake.def()
+    }
+
+    fn via() -> Option<RelationDef> {
+        Some(super::cake_filling::Relation::Filling.def().rev())
+    }
+}
+
+impl Model {
+    pub fn find_cake(&self) -> Select<super::cake::Entity> {
+        Entity::find_related().belongs_to::<Entity>(self)
+    }
+}

examples/sqlx-mysql/src/main.rs

@@ -150,5 +150,27 @@ async fn find_many_to_many(db: &Database) -> Result<(), QueryErr> {
         println!("{:?}\n", bb);
     }
 
+    print!("find fillings for cheese cake: ");
+
+    let cheese = cake::Entity::find_by(1).one(db).await?;
+
+    let fillings: Vec<filling::Model> = cheese.find_filling().all(db).await?;
+
+    println!();
+    for ff in fillings.iter() {
+        println!("{:?}\n", ff);
+    }
+
+    print!("find cakes for lemon: ");
+
+    let lemon = filling::Entity::find_by(2).one(db).await?;
+
+    let cakes: Vec<cake::Model> = lemon.find_cake().all(db).await?;
+
+    println!();
+    for cc in cakes.iter() {
+        println!("{:?}\n", cc);
+    }
+
     Ok(())
 }

src/entity/relation.rs

@@ -50,6 +50,19 @@ where
     to_col: Option<Identity>,
 }
 
+impl RelationDef {
+    /// Reverse this relation (swap from and to)
+    pub fn rev(self) -> Self {
+        Self {
+            rel_type: self.rel_type,
+            from_tbl: self.to_tbl,
+            to_tbl: self.from_tbl,
+            from_col: self.to_col,
+            to_col: self.from_col,
+        }
+    }
+}
+
 impl<E, R> RelationBuilder<E, R>
 where
     E: EntityTrait,

src/tests_cfg/cake.rs

@@ -25,7 +25,6 @@ pub enum PrimaryKey {
 #[derive(Copy, Clone, Debug, EnumIter)]
 pub enum Relation {
     Fruit,
-    CakeFilling,
 }
 
 impl ColumnTrait for Column {
@@ -46,10 +45,6 @@ impl RelationTrait for Relation {
                 .from(Column::Id)
                 .to(super::fruit::Column::CakeId)
                 .into(),
-            Self::CakeFilling => Entity::has_many(super::cake_filling::Entity)
-                .from(Column::Id)
-                .to(super::cake_filling::Column::CakeId)
-                .into(),
         }
     }
 }
@@ -66,7 +61,7 @@ impl Related<super::filling::Entity> for Entity {
     }
 
     fn via() -> Option<RelationDef> {
-        Some(Relation::CakeFilling.def())
+        Some(super::cake_filling::Relation::Cake.def().rev())
     }
 }
 
@@ -74,4 +69,8 @@ impl Model {
     pub fn find_fruit(&self) -> Select<super::fruit::Entity> {
         Entity::find_related().belongs_to::<Entity>(self)
     }
+
+    pub fn find_filling(&self) -> Select<super::filling::Entity> {
+        Entity::find_related().belongs_to::<Entity>(self)
+    }
 }

src/tests_cfg/cake_filling.rs

@@ -43,11 +43,11 @@ impl ColumnTrait for Column {
 impl RelationTrait for Relation {
     fn def(&self) -> RelationDef {
         match self {
-            Self::Cake => Entity::has_many(super::cake::Entity)
+            Self::Cake => Entity::has_one(super::cake::Entity)
                 .from(Column::CakeId)
                 .to(super::cake::Column::Id)
                 .into(),
-            Self::Filling => Entity::has_many(super::filling::Entity)
+            Self::Filling => Entity::has_one(super::filling::Entity)
                 .from(Column::FillingId)
                 .to(super::filling::Column::Id)
                 .into(),

src/tests_cfg/filling.rs

@@ -41,3 +41,19 @@ impl RelationTrait for Relation {
         panic!()
     }
 }
+
+impl Related<super::cake::Entity> for Entity {
+    fn to() -> RelationDef {
+        super::cake_filling::Relation::Cake.def()
+    }
+
+    fn via() -> Option<RelationDef> {
+        Some(super::cake_filling::Relation::Filling.def().rev())
+    }
+}
+
+impl Model {
+    pub fn find_cake(&self) -> Select<super::cake::Entity> {
+        Entity::find_related().belongs_to::<Entity>(self)
+    }
+}