Add find_by_relation method to QueryFilter and use it to eliminate unnecessary joins in ModelTrait

Author: rumpuslabs

src/entity/model.rs

@@ -1,7 +1,7 @@
 use crate::{
     find_linked, ActiveModelBehavior, ActiveModelTrait, ConnectionTrait, DbErr, DeleteResult,
-    EntityTrait, IntoActiveModel, Linked, QueryFilter, QueryResult, QueryTrait, Related, Select,
-    SelectModel, SelectorRaw, Statement,
+    EntityTrait, IntoActiveModel, Linked, QueryFilter, QueryResult, QuerySelect, QueryTrait,
+    Related, Select, SelectModel, SelectorRaw, Statement,
 };
 use async_trait::async_trait;
 pub use sea_query::{Alias, CommonTableExpression, IntoTableRef, JoinType, UnionType, Value};
@@ -25,16 +25,33 @@ pub trait ModelTrait: Clone + Send + Debug {
         R: EntityTrait,
         Self::Entity: Related<R>,
     {
-        <Self::Entity as Related<R>>::find_related().belongs_to(self)
+        let mut select = Select::<R>::new();
+        if let Some(via) = <Self::Entity as Related<R>>::via() {
+            select = select.join_rev(JoinType::InnerJoin, via)
+        }
+        select.find_by_relation(<Self::Entity as Related<R>>::to(), self, None)
     }
 
     /// Find linked Models
     fn find_linked<L>(&self, l: L) -> Select<L::ToEntity>
     where
         L: Linked<FromEntity = Self::Entity>,
     {
-        let tbl_alias = &format!("r{}", l.link().len() - 1);
-        l.find_linked().belongs_to_tbl_alias(self, tbl_alias)
+        let mut link = l.link().into_iter().peekable();
+        match link.next_if(|rel| rel.on_condition.is_none()) {
+            Some(last) => {
+                let tbl_alias = if link.len() == 0 {
+                    None
+                } else {
+                    Some(format!("r{}", link.len() - 1))
+                };
+                find_linked(link.rev(), JoinType::InnerJoin).find_by_relation(last, self, tbl_alias)
+            }
+            None => {
+                let tbl_alias = &format!("r{}", link.len() - 1);
+                find_linked(link.rev(), JoinType::InnerJoin).belongs_to_tbl_alias(self, tbl_alias)
+            }
+        }
     }
 
     /// Find linked Models, recursively

src/query/helper.rs

@@ -861,6 +861,24 @@ pub trait QueryFilter: Sized {
         }
         self
     }
+
+    /// Perform a check to determine table belongs to a Model through a relation
+    fn find_by_relation<M>(mut self, rel: RelationDef, model: &M, tbl_alias: Option<String>) -> Self
+    where
+        M: ModelTrait,
+    {
+        let tbl_alias = tbl_alias.unwrap_or_else(|| unpack_table_ref(&rel.to_tbl).to_string());
+        for (from_col, to_col) in rel.from_col.into_iter().zip(rel.to_col.into_iter()) {
+            let column = from_col
+                .to_string()
+                .parse()
+                .ok()
+                .expect("RelationDef should refer to valid column name");
+            let expr = Expr::col((Alias::new(&tbl_alias), to_col)).eq(model.get(column));
+            self = self.filter(expr);
+        }
+        self
+    }
 }
 
 pub(crate) fn join_condition(mut rel: RelationDef) -> Condition {

src/query/join.rs

@@ -199,8 +199,7 @@ mod tests {
                 .to_string(),
             [
                 "SELECT `fruit`.`id`, `fruit`.`name`, `fruit`.`cake_id` FROM `fruit`",
-                "INNER JOIN `cake` ON `cake`.`id` = `fruit`.`cake_id`",
-                "WHERE `cake`.`id` = 12",
+                "WHERE `fruit`.`cake_id` = 12",
             ]
             .join(" ")
         );
@@ -292,8 +291,7 @@ mod tests {
                 r#"SELECT `filling`.`id`, `filling`.`name`, `filling`.`vendor_id`"#,
                 r#"FROM `filling`"#,
                 r#"INNER JOIN `cake_filling` AS `r0` ON `r0`.`filling_id` = `filling`.`id`"#,
-                r#"INNER JOIN `cake` AS `r1` ON `r1`.`id` = `r0`.`cake_id`"#,
-                r#"WHERE `r1`.`id` = 12"#,
+                r#"WHERE `r0`.`cake_id` = 12"#,
             ]
             .join(" ")
         );
@@ -316,8 +314,7 @@ mod tests {
                 r#"FROM `vendor`"#,
                 r#"INNER JOIN `filling` AS `r0` ON `r0`.`vendor_id` = `vendor`.`id`"#,
                 r#"INNER JOIN `cake_filling` AS `r1` ON `r1`.`filling_id` = `r0`.`id`"#,
-                r#"INNER JOIN `cake` AS `r2` ON `r2`.`id` = `r1`.`cake_id`"#,
-                r#"WHERE `r2`.`id` = 18"#,
+                r#"WHERE `r1`.`cake_id` = 18"#,
             ]
             .join(" ")
         );