What is the best way to integrate external SQL Server data into my Django application for frontend display?

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Hello everyone,

I am making good progress with my first Django application and have successfully implemented my data model. Now I need to display data from another SQL Server database on the frontend without altering it in Django. My current setup is as follows:
• Django DB: Server01, DB Name = ‘Django’
• Other Data DB: Server02, DB Name = ‘Data’

I have temporarily created a model representing the external table in my models.py and use an ETL process to refresh the data, but this solution isn’t ideal. Specifically, I need to link purchasing positions with responsibilities by joining on the cost_bearer, department, and system fields between the Responsibility and BottleneckPart models.

Here is my current models.py:

PYTHON
from django.db import models

# Create your models here.
class Project(models.Model):
    cost_bearer = models.CharField(max_length=6, primary_key=True, verbose_name='Kostenträger')
    description = models.CharField(max_length=50, unique=True, verbose_name='Bezeichnung')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Projekt'
        verbose_name_plural = 'Projekte'

    def __str__(self):
        return f'{self.cost_bearer} {self.description}'

class System(models.Model):
    number = models.CharField(max_length=4, primary_key=True, verbose_name='Nummer')
    description = models.CharField(max_length=100, verbose_name='Bezeichnung')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Baugruppe'
        verbose_name_plural = 'Baugruppen'

    def __str__(self):
        return f'{self.number} {self.description}'

class Department(models.Model):
    name = models.CharField(max_length=50, unique=True, verbose_name='Name')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Abteilung'
        verbose_name_plural = 'Abteilungen'

    def __str__(self):
        return self.name

class Team(models.Model):
    department = models.ForeignKey(Department, on_delete=models.CASCADE, verbose_name='Abteilung')
    name = models.CharField(max_length=50, unique=True, verbose_name='Name')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Team'
        verbose_name_plural = 'Teams'

    def __str__(self):
        return self.name

class Employee(models.Model):
    team = models.ManyToManyField(Team, verbose_name='Team')
    user = models.OneToOneField('auth.User', on_delete=models.CASCADE, verbose_name='Benutzer')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Mitarbeiter'
        verbose_name_plural = 'Mitarbeiter'

    def __str__(self):
        return f'{self.user.first_name} {self.user.last_name}'

class Responsibility(models.Model):
    project = models.ForeignKey(Project, on_delete=models.CASCADE, verbose_name='Projekt')
    system = models.ForeignKey(System, on_delete=models.CASCADE, verbose_name='Baugruppe')
    team = models.ForeignKey(Team, on_delete=models.CASCADE, verbose_name='Team')
    employee = models.ForeignKey(Employee, on_delete=models.SET_NULL, blank=True, null=True, verbose_name='Mitarbeiter')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Verantwortlichkeit'
        verbose_name_plural = 'Verantwortlichkeiten'
        constraints = [
            models.UniqueConstraint(fields=['project', 'system', 'team', 'employee'], name='uq_project_system_team_employee')
        ]

    def __str__(self):
        return f'{self.project} | {self.system} | {self.team} | {self.employee}'

class Problem(models.Model):
    responsibility = models.ForeignKey(Responsibility, on_delete=models.CASCADE, verbose_name='Verantwortlichkeit')
    summary = models.CharField(max_length=150, verbose_name='Zusammenfassung')
    description = models.TextField(verbose_name='Beschreibung')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Problem'
        verbose_name_plural = 'Probleme'

    def __str__(self):
        return f'{self.responsibility} | {self.summary}'

class Solution(models.Model):
    problem = models.OneToOneField(Problem, on_delete=models.CASCADE, verbose_name='Problem')
    summary = models.CharField(max_length=150, verbose_name='Zusammenfassung')
    description = models.TextField(verbose_name='Beschreibung')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Lösung'
        verbose_name_plural = 'Lösungen'

    def __str__(self):
        return f'{self.problem} | {self.summary}'

class Status(models.Model):
    COLORS = (
        ('Rot', 'Rot'),
        ('Gelb', 'Gelb'),
        ('Grün', 'Grün'),
    )
    responsibility = models.OneToOneField(Responsibility, on_delete=models.CASCADE, unique=True, verbose_name='Verantwortlichkeit')
    traffic_light = models.CharField(max_length=4, choices=COLORS, default='Grün', verbose_name='Ampel')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Status'
        verbose_name_plural = 'Status'

    def __str__(self):
        return f'{self.responsibility} | {self.traffic_light}'

class BottleneckPart(models.Model):
    cost_bearer = models.ForeignKey(Project, on_delete=models.CASCADE, verbose_name='Kostenträger')
    department = models.ForeignKey(Department, on_delete=models.CASCADE, verbose_name='Abteilung')
    system = models.ForeignKey(System, on_delete=models.CASCADE, verbose_name='Baugruppe')
    feedback_number = models.IntegerField(verbose_name='Rückmeldenummer')
    feedback_position_number = models.CharField(max_length=6, verbose_name='Rückmeldepositionsnummer')
    description_head = models.CharField(max_length=150, verbose_name='Kopfbezeichnung')
    description = models.CharField(max_length=150, verbose_name='Bezeichnung')
    po_position_status = models.CharField(max_length=50, blank=True, null=True, verbose_name='Bestellpositionsstatus')
    inquiry_purchase_current = models.DateField(blank=True, null=True, verbose_name='Anfrage an KM IST')
    inquiry_purchase_target = models.DateField(blank=True, null=True, verbose_name='Anfrage an KM SOLL')
    purchase_requisition_planning_current = models.DateField(blank=True, null=True, verbose_name='Bestellanforderung an TP IST')
    purchase_requisition_planning_target = models.DateField(blank=True, null=True, verbose_name='Bestellanforderung an TP SOLL')
    po_finished_current = models.DateField(blank=True, null=True, verbose_name='Bestellung fertig IST')
    po_finished_target = models.DateField(blank=True, null=True, verbose_name='Bestellung fertig SOLL')
    appointment_document = models.CharField(max_length=50, blank=True, null=True, verbose_name='TU')
    appointment_document_date = models.DateField(blank=True, null=True, verbose_name='TU Termin')
    delivery_time_current = models.IntegerField(blank=True, null=True, verbose_name='Lieferzeit AT')
    delivery_date_target = models.DateField(blank=True, null=True, verbose_name='Liefertermin SOLL')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Engpassteil'
        verbose_name_plural = 'Engpassteile'

I appreciate any guidance on achieving a cleaner integration between the two databases.

Best regards,
gospat

Comments 0

•

Answers 1

•

1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

Using Multiple Databases in Django

To integrate your external SQL Server database with your Django application, you can use Django's multi-database support. This approach will allow you to query data from both databases without needing to use ETL processes to copy data between them.

Setting Up Multiple Databases

First, you need to configure both databases in your settings.py:

PYTHON
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlserver',  # Or appropriate engine
        'NAME': 'Django',
        'HOST': 'Server01',
        'USER': 'your_username',
        'PASSWORD': 'your_password',
    },
    'data_db': {
        'ENGINE': 'django.db.backends.sqlserver',  # Or appropriate engine
        'NAME': 'Data',
        'HOST': 'Server02',
        'USER': 'your_username',
        'PASSWORD': 'your_password',
    }
}

Creating a Database Router

Next, create a database router to direct queries to the appropriate database:

PYTHON
# routers.py
class MultiDBRouter:
    """
    Router to manage database operations for models in different databases.
    """
    def db_for_read(self, model, **hints):
        if model._meta.app_label == 'external_data':
            return 'data_db'
        return 'default'

    def db_for_write(self, model, **hints):
        if model._meta.app_label == 'external_data':
            return 'data_db'
        return 'default'

    def allow_relation(self, obj1, obj2, **hints):
        # Only allow relations within the same database
        return obj1._state.db == obj2._state.db

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        # Don't run migrations on the external database
        if db == 'data_db':
            return False
        if app_label == 'external_data':
            return False
        return True

Add the router to your settings:

PYTHON
DATABASE_ROUTERS = ['path.to.routers.MultiDBRouter']

Creating Models for External Data

Create a separate app for your external data models:

BASH
python manage.py startapp external_data

In your external_data/models.py, define models that match the external database schema:

PYTHON
from django.db import models

class ExternalBottleneckPart(models.Model):
    # Define fields matching your external table
    cost_bearer = models.CharField(max_length=6)
    department_id = models.IntegerField()
    system_id = models.CharField(max_length=4)
    feedback_number = models.IntegerField()
    # ... other fields ...

    class Meta:
        app_label = 'external_data'
        db_table = 'actual_table_name_in_external_db'
        managed = False  # Django won't try to create or modify this table

Querying Across Databases

Since Django doesn't support cross-database relationships, you'll need to handle the joining in your application code:

PYTHON
from django.db import connections
from django.db.models import Q
from your_app.models import Responsibility
from external_data.models import ExternalBottleneckPart

def get_related_data(responsibility_id):
    # Get the responsibility
    responsibility = Responsibility.objects.get(id=responsibility_id)
    
    # Query the external data
    external_parts = ExternalBottleneckPart.objects.using('data_db').filter(
        cost_bearer=responsibility.project.cost_bearer,
        system_id=responsibility.system.number,
        department_id=responsibility.team.department.id
    )
    
    return {
        'responsibility': responsibility,
        'external_parts': external_parts
    }

Using in Admin Interface

If you want to expose the external database in the admin interface, you'll need a custom ModelAdmin:

PYTHON
from django.contrib import admin
from external_data.models import ExternalBottleneckPart

class ExternalDataAdmin(admin.ModelAdmin):
    using = 'data_db'
    
    def save_model(self, request, obj, form, change):
        # Save to the external database
        obj.save(using=self.using)
    
    def delete_model(self, request, obj):
        obj.delete(using=self.using)
    
    def get_queryset(self, request):
        return super().get_queryset(request).using(self.using)
    
    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        return super().formfield_for_foreignkey(
            db_field, request, using=self.using, **kwargs
        )
    
    def formfield_for_manytomany(self, db_field, request, **kwargs):
        return super().formfield_for_manytomany(
            db_field, request, using=self.using, **kwargs
        )

admin.site.register(ExternalBottleneckPart, ExternalDataAdmin)

Important Limitations

Django doesn't support foreign key or many-to-many relationships spanning multiple databases.
You cannot create cross-database relationships due to referential integrity constraints.
If you're using the admin interface with multiple databases, you'll need custom ModelAdmin classes.

This approach allows you to query data from both databases without copying it, but you'll need to handle the relationships in your application code rather than relying on Django's ORM for cross-database joins.

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