diff --git a/examples/sqlx-mysql/src/example_cake.rs b/examples/sqlx-mysql/src/example_cake.rs
index 9438ac22..85207281 100644
--- a/examples/sqlx-mysql/src/example_cake.rs
+++ b/examples/sqlx-mysql/src/example_cake.rs
@@ -1,5 +1,5 @@
 use sea_orm::{
-    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic,
+    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic, PrimaryKeyOfModel,
     ModelTrait, QueryResult, Related, RelationDef, RelationTrait, Select, TypeErr, Value, PrimaryKeyTrait
 };
 
@@ -98,6 +98,15 @@ impl IdenStatic for PrimaryKey {
 // TODO: implement with derive macro
 impl PrimaryKeyTrait for PrimaryKey {}
 
+// TODO: implement with derive macro
+impl PrimaryKeyOfModel<Model> for PrimaryKey {
+    fn into_column(self) -> <Model as ModelTrait>::Column {
+        match self {
+            Self::Id => Column::Id,
+        }
+    }
+}
+
 impl RelationTrait for Relation {
     fn def(&self) -> RelationDef {
         match self {
diff --git a/examples/sqlx-mysql/src/example_fruit.rs b/examples/sqlx-mysql/src/example_fruit.rs
index 46a5bb9a..d994fbb2 100644
--- a/examples/sqlx-mysql/src/example_fruit.rs
+++ b/examples/sqlx-mysql/src/example_fruit.rs
@@ -1,5 +1,5 @@
 use sea_orm::{
-    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic,
+    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic, PrimaryKeyOfModel,
     ModelTrait, QueryResult, RelationDef, RelationTrait, TypeErr, Value, PrimaryKeyTrait
 };
 
@@ -103,6 +103,15 @@ impl IdenStatic for PrimaryKey {
 // TODO: implement with derive macro
 impl PrimaryKeyTrait for PrimaryKey {}
 
+// TODO: implement with derive macro
+impl PrimaryKeyOfModel<Model> for PrimaryKey {
+    fn into_column(self) -> <Model as ModelTrait>::Column {
+        match self {
+            Self::Id => Column::Id,
+        }
+    }
+}
+
 impl RelationTrait for Relation {
     fn def(&self) -> RelationDef {
         panic!()
diff --git a/examples/sqlx-mysql/src/main.rs b/examples/sqlx-mysql/src/main.rs
index 72048897..f817aacb 100644
--- a/examples/sqlx-mysql/src/main.rs
+++ b/examples/sqlx-mysql/src/main.rs
@@ -32,4 +32,14 @@ async fn main() {
     println!();
     println!("{:?}", cheese);
     println!();
+
+    println!("find models belongs to");
+
+    let fruits = cheese.find_fruit().all(&db).await.unwrap();
+
+    println!();
+    for ff in fruits.iter() {
+        println!("{:?}", ff);
+        println!();
+    }
 }
diff --git a/src/entity/primary_key.rs b/src/entity/primary_key.rs
index 357b1314..744d7d45 100644
--- a/src/entity/primary_key.rs
+++ b/src/entity/primary_key.rs
@@ -1,3 +1,10 @@
-use super::IdenStatic;
+use super::{ModelTrait, IdenStatic};
 
-pub trait PrimaryKeyTrait: IdenStatic {}
\ No newline at end of file
+pub trait PrimaryKeyTrait: IdenStatic {}
+
+pub trait PrimaryKeyOfModel<M>
+where
+    M: ModelTrait,
+{
+    fn into_column(self) -> M::Column;
+}
\ No newline at end of file
diff --git a/src/query/select.rs b/src/query/select.rs
index 596d1bd9..fea847c1 100644
--- a/src/query/select.rs
+++ b/src/query/select.rs
@@ -1,4 +1,4 @@
-use crate::{EntityTrait, Identity, Iterable, RelationDef, RelationTrait, Statement, Related};
+use crate::{EntityTrait, Identity, Iterable, PrimaryKeyOfModel, RelationDef, RelationTrait, Statement, Related};
 use core::fmt::Debug;
 use core::marker::PhantomData;
 pub use sea_query::JoinType;
@@ -88,13 +88,16 @@ where
     }
 
     pub fn belongs_to<R>(self, model: &R::Model) -> Self
-        where R: EntityTrait + Related<E> {
-        // match R::primary_key() {
-        //     Identity::Unary(iden) => {
-        //         model.get(iden)
-        //     }
-        // };
-        self
+        where R: EntityTrait + Related<E>, R::PrimaryKey: PrimaryKeyOfModel<R::Model> {
+        use crate::{ColumnTrait, ModelTrait};
+
+        if let Some(key) = R::PrimaryKey::iter().next() {
+            // TODO: supporting composite primary key
+            let col = key.into_column();
+            self.filter(col.eq(model.get(col)))
+        } else {
+            panic!("undefined primary key");
+        }
     }
 
     /// ```
@@ -243,4 +246,25 @@ mod tests {
             .join(" ")
         );
     }
+
+    #[test]
+    fn join_5() {
+
+        let cake_model = cake::Model {
+            id: 12,
+            name: "".to_owned(),
+        };
+
+        assert_eq!(
+            cake_model.find_fruit()
+                .build(MysqlQueryBuilder)
+                .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",
+            ]
+            .join(" ")
+        );
+    }
 }
diff --git a/src/tests_cfg/cake.rs b/src/tests_cfg/cake.rs
index 9951a857..db96d95a 100644
--- a/src/tests_cfg/cake.rs
+++ b/src/tests_cfg/cake.rs
@@ -1,5 +1,5 @@
 use crate::{
-    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic,
+    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic, PrimaryKeyOfModel,
     ModelTrait, QueryResult, Related, RelationDef, RelationTrait, Select, TypeErr, Value, PrimaryKeyTrait
 };
 
@@ -98,6 +98,15 @@ impl IdenStatic for PrimaryKey {
 // TODO: implement with derive macro
 impl PrimaryKeyTrait for PrimaryKey {}
 
+// TODO: implement with derive macro
+impl PrimaryKeyOfModel<Model> for PrimaryKey {
+    fn into_column(self) -> <Model as ModelTrait>::Column {
+        match self {
+            Self::Id => Column::Id,
+        }
+    }
+}
+
 impl RelationTrait for Relation {
     fn def(&self) -> RelationDef {
         match self {
diff --git a/src/tests_cfg/fruit.rs b/src/tests_cfg/fruit.rs
index 93c9e4a3..e3762afd 100644
--- a/src/tests_cfg/fruit.rs
+++ b/src/tests_cfg/fruit.rs
@@ -1,5 +1,5 @@
 use crate::{
-    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic,
+    ColumnTrait, ColumnType, EntityTrait, EnumIter, Iden, IdenStatic, PrimaryKeyOfModel,
     ModelTrait, QueryResult, RelationDef, RelationTrait, TypeErr, Value, PrimaryKeyTrait
 };
 
@@ -103,6 +103,15 @@ impl IdenStatic for PrimaryKey {
 // TODO: implement with derive macro
 impl PrimaryKeyTrait for PrimaryKey {}
 
+// TODO: implement with derive macro
+impl PrimaryKeyOfModel<Model> for PrimaryKey {
+    fn into_column(self) -> <Model as ModelTrait>::Column {
+        match self {
+            Self::Id => Column::Id,
+        }
+    }
+}
+
 impl RelationTrait for Relation {
     fn def(&self) -> RelationDef {
         panic!()