Fix multiple M2M relations on one table, close #3347

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
@@ -290,11 +296,12 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 	}
 
 	// build references
-	for idx, f := range relation.JoinTable.Fields {
+	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[idx] = f
+			relation.JoinTable.PrimaryFields = append(relation.JoinTable.PrimaryFields, f)
 			ownPriamryField := schema == fieldsMap[f.Name].Schema && ownFieldsMap[f.Name]
 
 			if ownPriamryField {
@@ -322,6 +329,7 @@ func (schema *Schema) buildMany2ManyRelation(relation *Relationship, field *Fiel
 			})
 		}
 	}
+}
 
 type guessLevel int
 

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},
+			},
+		},
+	)
+}