Be able to find many to many relations

association.go

@@ -1,25 +1,67 @@
 package gorm
 
+import (
+	"errors"
+	"fmt"
+	"reflect"
+)
+
 type Association struct {
 	Scope  *Scope
 	Column string
+	Error  error
 }
 
-func (*Association) Find(value interface{}) {
+func (association *Association) Find(value interface{}) *Association {
+	scope := association.Scope
+	primaryKey := scope.PrimaryKeyValue()
+	if reflect.DeepEqual(reflect.ValueOf(primaryKey), reflect.Zero(reflect.ValueOf(primaryKey).Type())) {
+		association.Error = errors.New("primary key can't be nil")
+	}
+
+	scopeType := scope.IndirectValue().Type()
+	if f, ok := scopeType.FieldByName(SnakeToUpperCamel(association.Column)); ok {
+		field := scope.fieldFromStruct(f)
+		joinTable := field.JoinTable
+		if joinTable != nil && joinTable.foreignKey != "" {
+			if joinTable.joinTable != "" {
+				newScope := scope.New(value)
+				joinSql := fmt.Sprintf(
+					"INNER JOIN %v ON %v.%v = %v.%v",
+					scope.Quote(joinTable.joinTable),
+					scope.Quote(joinTable.joinTable),
+					scope.Quote(ToSnake(joinTable.associationForeignKey)),
+					newScope.QuotedTableName(),
+					scope.Quote(newScope.PrimaryKey()))
+				whereSql := fmt.Sprintf("%v.%v = ?", scope.Quote(joinTable.joinTable), scope.Quote(ToSnake(joinTable.foreignKey)))
+				scope.db.Joins(joinSql).Where(whereSql, primaryKey).Find(value)
+			} else {
+			}
+		} else {
+			association.Error = errors.New(fmt.Sprintf("invalid association %v for %v", association.Column, scopeType))
+		}
+	} else {
+		association.Error = errors.New(fmt.Sprintf("%v doesn't have column %v", scopeType, association.Column))
+	}
+	return association
 }
 
-func (*Association) Append(values interface{}) {
+func (association *Association) Append(values interface{}) *Association {
+	return association
 }
 
-func (*Association) Delete(value interface{}) {
+func (association *Association) Delete(value interface{}) *Association {
+	return association
 }
 
-func (*Association) Clear(value interface{}) {
+func (association *Association) Clear(value interface{}) *Association {
+	return association
 }
 
-func (*Association) Replace(values interface{}) {
+func (association *Association) Replace(values interface{}) *Association {
+	return association
 }
 
-func (*Association) Count(values interface{}) int {
+func (association *Association) Count(values interface{}) int {
 	return 0
 }

association_test.go

@@ -140,7 +140,7 @@ func TestManyToMany(t *testing.T) {
 	newLanguages = []Language{}
 	db.Model(&user).Association("Languages").Find(&newLanguages)
 	if len(newLanguages) != 3 {
-		t.Errorf("Query many to many relations")
+		t.Errorf("Should be able to find many to many relations")
 	}
 
 	// db.Model(&User{}).Many2Many("Languages").Add(&Language{})

migration_test.go

@@ -18,7 +18,7 @@ func runMigration() {
 	db.Exec("drop table roles")
 	db.Exec("drop table companies")
 	db.Exec("drop table animals")
-	db.Exec("drop table user_companies")
+	db.Exec("drop table user_languages")
 
 	if err := db.CreateTable(&Animal{}).Error; err != nil {
 		panic(fmt.Sprintf("No error should happen when create table, but got %+v", err))