Day 21 國際化租屋，Django 多租戶多語系

即便是在同一個國家也可能會有不同的文化，每個租戶的語言習慣也可能會不相同，一個詞在不同領域也可能會有不一樣的解釋。今天要來介紹在 Django 多租戶架構下的多語系，除了能區分不同租戶的翻譯對照表之外，還能在管理介面直接修改，我們馬上開始吧！

調整多語系目錄結構

由於 Django 的多語系是讀取編譯後的檔案，我們將要建立一個新多語系目錄，並且在其中使用租戶的 schema 名稱建立各自的多語系目錄。

docker exec --workdir /opt/app/web example_tenant_web \
mkdir tenant_locale

docker exec --workdir /opt/app/web example_tenant_web \
cp -pr locale tenant_locale/example01

docker exec --workdir /opt/app/web example_tenant_web \
cp -pr locale tenant_locale/example02

新目錄結構如下

.
├── core
├── customers
├── locale
│   └── zh_Hant
│       └── LC_MESSAGES
│           └── django.po
├── main
├── manage.py
├── media
├── products
└── tenant_locale
    ├── example01
    │   └── zh_Hant
    │       └── LC_MESSAGES
    │           ├── django.mo
    │           └── django.po
    └── example02
        └── zh_Hant
            └── LC_MESSAGES
                ├── django.mo
                └── django.po

建立 翻譯對照表

在 core 新增模型 LocaleSetting 與 TranslateSetting 用來定義多語系的翻譯對照表

為了避免在同一個對照表建立重複的翻譯詞，使用 clean 函數進行重複判斷。

# core/models.py

from django.core.exceptions import ValidationError
from django.db import models
from django.utils.translation import gettext_lazy as _
from core import helpers

# ...

class LocaleSetting(models.Model):
    id = models.CharField('語言代碼', max_length=10, primary_key=True)
    language = models.CharField('系統語言', max_length=50)

    class Meta:
        verbose_name = '翻譯對照表'
        verbose_name_plural = '翻譯對照表'

    def __str__(self):
        return "%s" % (self.id)

class TranslateSetting(models.Model):
    locale = models.ForeignKey('core.LocaleSetting', on_delete=models.CASCADE, related_name='translatesetting_set')
    raw_string = models.CharField('原始文字', max_length=255)
    translated_string = models.CharField('翻譯後文字', default='', null=True, max_length=255, blank=True)

    def clean(self):
        if trans_obj := TranslateSetting.objects.filter(raw_string=self.raw_string, locale=self.locale):
            if self.id != trans_obj.first().id:
                raise ValidationError(_('Raw string already exists!'))

    class Meta:
        verbose_name = '翻譯文字'
        verbose_name_plural = '翻譯文字'
        ordering = ['raw_string']

    def __str__(self):
        return ""

建立資料庫遷移檔案

docker exec --workdir /opt/app/web example_tenant_web \
    python3.10 manage.py makemigrations
...

Migrations for 'core':
  core/migrations/0005_localesetting_translatesetting.py
    - Create model LocaleSetting
    - Create model TranslateSetting

執行資料庫遷移

docker exec --workdir /opt/app/web example_tenant_web \
    python3.10 manage.py migrate

... 

=== Starting migration
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, core, customers, products, sessions, sites
Running migrations:
  Applying core.0005_localesetting_translatesetting...
 OK
=== Starting migration
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, core, customers, products, sessions, sites
Running migrations:
  Applying core.0005_localesetting_translatesetting...
 OK
=== Starting migration
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, core, customers, products, sessions, sites
Running migrations:
  Applying core.0005_localesetting_translatesetting...
 OK

新增 翻譯對照表管理介面

# core/admin.py

import os
from django.conf import settings
from django.contrib import admin
from django.db import connection
from django.utils.translation import to_locale

# Register your models here.
from core.models import Setting, LocaleSetting, TranslateSetting

class SettingAdmin(admin.ModelAdmin):
    # ...

class TranslateSettingInline(admin.TabularInline):
    model = TranslateSetting
    fields = ('raw_string', 'translated_string')

class LocaleSettingAdmin(admin.ModelAdmin):
    search_fields = ['id', 'language']
    fields = ('id', 'language')
    list_display = ('id', 'language')
    inlines = [TranslateSettingInline, ]

admin.site.register(Setting, SettingAdmin) 
admin.site.register(LocaleSetting, LocaleSettingAdmin)

自動編譯語言檔

save_related 在儲存頁面時觸發，可以取得 inline 表送出後的中的所有值，我們將根據欄位內容重新寫一個 django.po 檔。
to_locale 為 Django 自帶的函數，可以將 zh-hant 轉換為 zh_Hant 格式，再加上當前的 schema 名稱來尋找多語系目錄的路徑後進行檔案覆蓋，而因為 django 的編譯指令需要指定語言代碼，這裡使用 gettext 的指令 msgfmt 來進行語言檔編譯。

# core/admin.py

import os
from django.conf import settings
from django.contrib import admin
from django.db import connection
from django.utils.translation import to_locale

class SettingAdmin(admin.ModelAdmin):
    # ...

class TranslateSettingInline(admin.TabularInline):
     # ...

class LocaleSettingAdmin(admin.ModelAdmin):
    search_fields = ['id', 'language']
    fields = ('id', 'language')
    list_display = ('id', 'language')
    inlines = [TranslateSettingInline, ]

    def save_related(self, request, form, formsets, change):
        super(LocaleSettingAdmin, self).save_related(request, form, formsets, change)
        locale_id = (to_locale(form.instance.id))
        locale_path = os.path.join(settings.BASE_DIR, f'tenant_locale/{connection.schema_name}/{locale_id}/LC_MESSAGES/')
        message_file = 'msgid ""\n' + \
        'msgstr ""\n' + \
        '"Project-Id-Version: PACKAGE VERSION\\n"\n' + \
        '"Report-Msgid-Bugs-To: \\n"\n' + \
        '"POT-Creation-Date: 2022-10-01 15:59+0800\\n"\n' + \
        '"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\\n"\n' + \
        '"Last-Translator: FULL NAME <EMAIL@ADDRESS>\\n"\n' + \
        '"Language-Team: LANGUAGE <LL@li.org>\\n"\n' + \
        '"Language: \\n"\n' + \
        '"MIME-Version: 1.0\\n"\n' + \
        '"Content-Type: text/plain; charset=UTF-8\\n"\n' + \
        '"Content-Transfer-Encoding: 8bit\\n"\n' + \
        '"Plural-Forms: nplurals=1; plural=0;\\n"\n\n'
        for trans_obj in form.instance.translatesetting_set.all():
            message_file += f'msgid "{trans_obj.raw_string}"\n'
            message_file += f'msgstr "{trans_obj.translated_string}"\n\n'
        with open(f"{locale_path}/django.po" , "w") as f:
            f.write(message_file)
        os.system(f"cd {locale_path} && msgfmt django.po -o django.mo")

讀取多語系

Django 本身會對語言檔進行快取，而這會造成在不同租戶無法正常取得各自的多語系檔案，我們需要在 middleware 將語言檔快取清除後重新取得多語系設定。

在 core 建立一個 middleware.py 並定義一個 TranslationsMiddleware 類

# core/middleware.py 

class TranslationsMiddleware(MiddlewareMixin):
    def process_request(self, request):
        from django.utils import translation
        from django.utils.translation import trans_real, get_language
        from django.conf import settings
        import gettext
        if settings.USE_I18N:
            try:
                # Reset gettext.GNUTranslation cache.
                gettext._translations = {}

                # Reset Django by-language translation cache.
                trans_real._translations = {}

                # Delete Django current language translation cache.
                trans_real._default = None

                settings.LOCALE_PATHS = (os.path.join(settings.BASE_DIR, f'tenant_locale/{connection.schema_name}'), )
                translation.activate(get_language())
            except AttributeError:
                pass

在 settings.py 的 MIDDLEWARE 加入 TranslationsMiddleware。

# main/settings.py

MIDDLEWARE = (
     ...
     'core.middleware.TranslationsMiddleware',
)

到這裡，多租戶多語系的設定就完成了！

頁面展示

租戶 examle01

對照表：
Home page 對照 首頁
List of products 對照 商品列表
Product detail 對照 商品詳情

展示：

租戶 example02

對照表：
Home page 對照 主頁
List of products 對照 商品清單
Product detail 對照 商品詳細

展示：

為了定期通知用戶上架的新品，我們接下來要講解如何使用 Django 寄信，下一回『 郵差來送信，使用 Django 寄送郵件 』。