refactor: prepare to decouple the "model migration" package and "models" package (#38533)

Migrations should never use model structs directly, because the model
structs can be different in different releases. e.g. if one migration uses
"User" model, it works in the early releases, then one day, when the
User model changes, the migration breaks because it will use the
new (incorrect) User model, it should only use the old User model.

The same to "modules/structs".

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

modelmigration/v1_16/v193_test.go

@@ -0,0 +1,80 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_16
+
+import (
+	"testing"
+
+	"gitea.dev/modelmigration/migrationtest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_AddRepoIDForAttachment(t *testing.T) {
+	type Attachment struct {
+		ID         int64  `xorm:"pk autoincr"`
+		UUID       string `xorm:"uuid UNIQUE"`
+		IssueID    int64  `xorm:"INDEX"` // maybe zero when creating
+		ReleaseID  int64  `xorm:"INDEX"` // maybe zero when creating
+		UploaderID int64  `xorm:"INDEX DEFAULT 0"`
+	}
+
+	type Issue struct {
+		ID     int64
+		RepoID int64
+	}
+
+	type Release struct {
+		ID     int64
+		RepoID int64
+	}
+
+	// Prepare and load the testing database
+	x, deferrable := migrationtest.PrepareTestEnv(t, 0, new(Attachment), new(Issue), new(Release))
+	defer deferrable()
+	if x == nil || t.Failed() {
+		return
+	}
+
+	// Run the migration
+	if err := AddRepoIDForAttachment(x); err != nil {
+		assert.NoError(t, err)
+		return
+	}
+
+	type NewAttachment struct {
+		ID         int64  `xorm:"pk autoincr"`
+		UUID       string `xorm:"uuid UNIQUE"`
+		RepoID     int64  `xorm:"INDEX"` // this should not be zero
+		IssueID    int64  `xorm:"INDEX"` // maybe zero when creating
+		ReleaseID  int64  `xorm:"INDEX"` // maybe zero when creating
+		UploaderID int64  `xorm:"INDEX DEFAULT 0"`
+	}
+
+	var issueAttachments []*NewAttachment
+	err := x.Table("attachment").Where("issue_id > 0").Find(&issueAttachments)
+	assert.NoError(t, err)
+	for _, attach := range issueAttachments {
+		assert.Positive(t, attach.RepoID)
+		assert.Positive(t, attach.IssueID)
+		var issue Issue
+		has, err := x.ID(attach.IssueID).Get(&issue)
+		assert.NoError(t, err)
+		assert.True(t, has)
+		assert.Equal(t, attach.RepoID, issue.RepoID)
+	}
+
+	var releaseAttachments []*NewAttachment
+	err = x.Table("attachment").Where("release_id > 0").Find(&releaseAttachments)
+	assert.NoError(t, err)
+	for _, attach := range releaseAttachments {
+		assert.Positive(t, attach.RepoID)
+		assert.Positive(t, attach.ReleaseID)
+		var release Release
+		has, err := x.ID(attach.ReleaseID).Get(&release)
+		assert.NoError(t, err)
+		assert.True(t, has)
+		assert.Equal(t, attach.RepoID, release.RepoID)
+	}
+}