Represent several relations between same types

[billy1624]

Resolve #89

[billy1624]

Just a simple POC @tyt2y3

[tyt2y3]

okay looks reasonable. But the intention of find_related is to select the ToEntity, and thus, it walks backwards from ToEntity back to FromEntity

[billy1624]

okay looks reasonable. But the intention of find_related is to select the ToEntity, and thus, it walks backwards from ToEntity back to FromEntity

I walk (join) in the wrong direction here?

sea-orm/src/entity/relation.rs

Lines 38 to 44 in 31941d3

	fn find_linked() -> Select<Self::ToEntity> {
	let mut select = Select::new();
	for rel in Self::link() {
	select = select.join(JoinType::InnerJoin, rel);
	}
	select
	}

[tyt2y3]

I think we were using join_rev

sea-orm/src/entity/relation.rs

Lines 26 to 28 in 8cfa142

	fn find_related() -> Select<R> {
	Select::<R>::new().join_join_rev(JoinType::InnerJoin, Self::to(), Self::via())
	}

sea-orm/src/query/helper.rs

Lines 121 to 127 in 8cfa142

	fn join_join_rev(mut self, join: JoinType, rel: RelationDef, via: Option<RelationDef>) -> Self {
	self = self.join_rev(join, rel);
	if let Some(via) = via {
	self = self.join_rev(join, via)
	}
	self
	}

[billy1624]

I don't understand why we need join_rev here.

sea-orm/src/entity/relation.rs

Lines 38 to 44 in 31941d3

	fn find_linked() -> Select<Self::ToEntity> {
	let mut select = Select::new();
	for rel in Self::link() {
	select = select.join(JoinType::InnerJoin, rel);
	}
	select
	}

sea-orm/src/query/join.rs

Lines 62 to 72 in 31941d3

	pub fn find_also_linked<L, T>(self, _: 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())
	}

Check these two test cases and see if the resulting SQL statements are expected

sea-orm/src/query/join.rs

Lines 237 to 275 in 31941d3

	#[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`.`id` = `cake_filling`.`cake_id`"#,
	r#"INNER JOIN `filling` ON `cake_filling`.`filling_id` = `filling`.`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(" ")
	);
	}

[tyt2y3]

sea-orm/src/query/join.rs

Lines 250 to 253 in 31941d3

	r#"SELECT `filling`.`id`, `filling`.`name`"#,
	r#"FROM `filling`"#,
	r#"INNER JOIN `cake_filling` ON `cake`.`id` = `cake_filling`.`cake_id`"#,
	r#"INNER JOIN `filling` ON `cake_filling`.`filling_id` = `filling`.`id`"#,

Well filling inner join filling, this is not right right?

I think ideally this simple case should matches the original Related implementation.

sea-orm/src/query/join.rs

Lines 171 to 184 in 8cfa142

	fn join_7() {
	use crate::{Related, Select};
	let find_filling: Select<filling::Entity> = cake::Entity::find_related();
	assert_eq!(
	find_filling.build(DbBackend::MySql).to_string(),
	[
	"SELECT `filling`.`id`, `filling`.`name` FROM `filling`",
	"INNER JOIN `cake_filling` ON `cake_filling`.`filling_id` = `filling`.`id`",
	"INNER JOIN `cake` ON `cake`.`id` = `cake_filling`.`cake_id`",
	]
	.join(" ")
	);
	}

[billy1624]

I see what you mean now. See 447947e for the fix.

[billy1624]

I also added test cases. Anything is still missing?

[nicoulaj]

This looks nice 👍

What about sea-orm-cli codegen though ? Maybe it could have a flag to generate Linked instead of Related for all associations as a first step ?

[billy1624]

This looks nice 👍

What about sea-orm-cli codegen though ? Maybe it could have a flag to generate Linked instead of Related for all associations as a first step ?

But generating Linked for all associations will be annoying loll

i.e. each table will be Linked to all other tables in some way unless it has no association with any table

[tyt2y3]

For the scope of this PR we are not changing the codegen.
But as a rough idea, I think these 'links' does not belong to the Entity file.
I am thinking to put them in a dedicated module because it works across many Entities.