From 162367be7d1d10aa59dc08bb507c356b4495c95e Mon Sep 17 00:00:00 2001
From: Jinzhu <wosmvp@gmail.com>
Date: Tue, 1 Sep 2020 11:30:16 +0800
Subject: [PATCH] Fix multiple M2M relations on one table, close #3347

---
 schema/relationship.go      | 62 +++++++++++++++++++++----------------
 schema/relationship_test.go | 31 +++++++++++++++++++
 2 files changed, 66 insertions(+), 27 deletions(-)

diff --git a/schema/relationship.go b/schema/relationship.go
index 5132ff74..aa992b84 100644
--- a/schema/relationship.go
+++ b/schema/relationship.go
@@ -254,12 +254,18 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 		})
 	}
 
+	joinTableFields = append(joinTableFields, reflect.StructField{
+		Name: schema.Name + field.Name,
+		Type: schema.ModelType,
+		Tag:  `gorm:"-"`,
+	})
+
 	if relation.JoinTable, err = Parse(reflect.New(reflect.StructOf(joinTableFields)).Interface(), schema.cacheStore, schema.namer); err != nil {
 		schema.err = err
 	}
 	relation.JoinTable.Name = many2many
 	relation.JoinTable.Table = schema.namer.JoinTableName(many2many)
-	relation.JoinTable.PrimaryFields = make([]*Field, len(relation.JoinTable.Fields))
+	relation.JoinTable.PrimaryFields = make([]*Field, 0, len(relation.JoinTable.Fields))
 
 	relName := relation.Schema.Name
 	relRefName := relation.FieldSchema.Name
@@ -290,36 +296,38 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 	}
 
 	// build references
-	for idx, f := range relation.JoinTable.Fields {
-		// use same data type for foreign keys
-		f.DataType = fieldsMap[f.Name].DataType
-		f.GORMDataType = fieldsMap[f.Name].GORMDataType
-		relation.JoinTable.PrimaryFields[idx] = f
-		ownPriamryField := schema == fieldsMap[f.Name].Schema && ownFieldsMap[f.Name]
+	for _, f := range relation.JoinTable.Fields {
+		if f.Creatable {
+			// use same data type for foreign keys
+			f.DataType = fieldsMap[f.Name].DataType
+			f.GORMDataType = fieldsMap[f.Name].GORMDataType
+			relation.JoinTable.PrimaryFields = append(relation.JoinTable.PrimaryFields, f)
+			ownPriamryField := schema == fieldsMap[f.Name].Schema && ownFieldsMap[f.Name]
 
-		if ownPriamryField {
-			joinRel := relation.JoinTable.Relationships.Relations[relName]
-			joinRel.Field = relation.Field
-			joinRel.References = append(joinRel.References, &Reference{
-				PrimaryKey: fieldsMap[f.Name],
-				ForeignKey: f,
-			})
-		} else {
-			joinRefRel := relation.JoinTable.Relationships.Relations[relRefName]
-			if joinRefRel.Field == nil {
-				joinRefRel.Field = relation.Field
+			if ownPriamryField {
+				joinRel := relation.JoinTable.Relationships.Relations[relName]
+				joinRel.Field = relation.Field
+				joinRel.References = append(joinRel.References, &Reference{
+					PrimaryKey: fieldsMap[f.Name],
+					ForeignKey: f,
+				})
+			} else {
+				joinRefRel := relation.JoinTable.Relationships.Relations[relRefName]
+				if joinRefRel.Field == nil {
+					joinRefRel.Field = relation.Field
+				}
+				joinRefRel.References = append(joinRefRel.References, &Reference{
+					PrimaryKey: fieldsMap[f.Name],
+					ForeignKey: f,
+				})
 			}
-			joinRefRel.References = append(joinRefRel.References, &Reference{
-				PrimaryKey: fieldsMap[f.Name],
-				ForeignKey: f,
+
+			relation.References = append(relation.References, &Reference{
+				PrimaryKey:    fieldsMap[f.Name],
+				ForeignKey:    f,
+				OwnPrimaryKey: ownPriamryField,
 			})
 		}
-
-		relation.References = append(relation.References, &Reference{
-			PrimaryKey:    fieldsMap[f.Name],
-			ForeignKey:    f,
-			OwnPrimaryKey: ownPriamryField,
-		})
 	}
 }
 
diff --git a/schema/relationship_test.go b/schema/relationship_test.go
index 2e85c538..f2d63323 100644
--- a/schema/relationship_test.go
+++ b/schema/relationship_test.go
@@ -267,3 +267,34 @@ func TestMany2ManyWithMultiPrimaryKeys(t *testing.T) {
 		},
 	)
 }
+
+func TestMultipleMany2Many(t *testing.T) {
+	type Thing struct {
+		ID int
+	}
+
+	type Person struct {
+		ID       int
+		Likes    []Thing `gorm:"many2many:likes"`
+		Dislikes []Thing `gorm:"many2many:dislikes"`
+	}
+
+	checkStructRelation(t, &Person{},
+		Relation{
+			Name: "Likes", Type: schema.Many2Many, Schema: "Person", FieldSchema: "Thing",
+			JoinTable: JoinTable{Name: "likes", Table: "likes"},
+			References: []Reference{
+				{"ID", "Person", "PersonID", "likes", "", true},
+				{"ID", "Thing", "ThingID", "likes", "", false},
+			},
+		},
+		Relation{
+			Name: "Dislikes", Type: schema.Many2Many, Schema: "Person", FieldSchema: "Thing",
+			JoinTable: JoinTable{Name: "dislikes", Table: "dislikes"},
+			References: []Reference{
+				{"ID", "Person", "PersonID", "dislikes", "", true},
+				{"ID", "Thing", "ThingID", "dislikes", "", false},
+			},
+		},
+	)
+}