Django API, manage linked tabes using multiple GETs - python-3.x

Question

In my django app i expose two tables using DjangoRestAPI for manage data one related to other.
There is a result data with this structure:
"results": [
{
"id": 175194,
"device": "f906e9db70b0cc822cb44ccd1b2b89a7",
"res_key": "b865c3125cb4ef173e55377026d94b2b",
"read_date": "2021-03-31T07:06:04.143569Z",
"unit": 2
},
{
"id": 21278,
"device": "f906e9db70b0cc822cb44ccd1b2b89a7",
"res_key": "c8a961f3ef9f8fa0ebdac3c910070055",
"read_date": "2021-03-26T15:54:04.171926Z",
"unit": 1
},
{
"id": 25173,
"device": "f906e9db70b0cc822cb44ccd1b2b89a7",
"res_key": "75126c6b2b4e78fc553ec75c7eb927ea",
"read_date": "2021-03-26T16:48:03.259185Z",
"unit": 1
},
...
and a result_details API endpoint related to results:
"results_details": [
{
"id": 1,
"id_res": 236,
"var_id": 1,
"var_val": "[41]",
"var_hash": "6f241d5445cf3031f6420de63c0a409bad527ea3"
},
{
"id": 2,
"id_res": 326,
"var_id": 1,
"var_val": "[45]",
"var_hash": "e5f03cfbed7ee88445b44ddf8e64365da310f8ec"
},
...
My models:
class Results(models.Model):
id = models.AutoField(primary_key=True)
device = models.ForeignKey(Device, null=True, on_delete=models.SET_NULL)
res_key = models.SlugField(max_length=80, verbose_name="Message unique key", unique=True)
read_date = models.DateTimeField(verbose_name="Datetime of vals readings")
unit = models.ForeignKey(ModbusDevice, null=True, on_delete=models.SET_NULL)
def __str__(self):
return self.device
class Meta:
indexes = [
models.Index(fields=['device', 'unit']),
]
"""
Detailed vars results table
"""
class VarsResults(models.Model):
id = models.AutoField(primary_key=True)
id_res = models.ForeignKey(Results, related_name="mainres", on_delete=models.CASCADE)
var_id = models.ForeignKey(ModbusVariable, null=True, on_delete=models.SET_NULL)
var_val = models.CharField(max_length=400, blank=True)
var_hash = models.CharField(max_length=400)
def __str__(self):
return self.var_hash
class Meta:
indexes = [
models.Index(fields=['id_res', 'var_id']),
]
Here my serializers:
class ResultsSerializer(serializers.ModelSerializer):
#main_res = serializers.RelatedField(read_only=True)
class Meta:
model = Results
fields = ['id', 'device', 'res_key', 'read_date', 'unit']
class VarsResultsSerializer(serializers.ModelSerializer):
id_res = serializers.ReadOnlyField(source='id_res.id')
class Meta:
model = VarsResults
fields = ['id', 'id_res', 'var_id', 'var_val', 'var_hash']
there is an id_res field that link to main results data.
So, in this configuration, every time a user have to get results related to a specific device have to execute a GET to the first table filtering for device and then, inside a for loop, manage n GETs on second table passing the id for link to id_res.
If i find 100 rows from Results API call i have to execute 100 different calls to the Results_data.
Someone have an idea for better manage this king of situation from external API calls?
I try to avoid internal data aggregation, i would external apps after API call manage internally data structure.
So many thanks in advance

Answer 1

Django automatically adds entity_id column for foreign keys. It's not only a bad practice to add them manually but it might also break a few things.
docs
Behind the scenes, Django appends "_id" to the field name to create its database column name. In the above example, the database table for the Car model will have a manufacturer_id column. (You can change this explicitly by specifying db_column) However, your code should never have to deal with the database column name, unless you write custom SQL. You’ll always deal with the field names of your model object.
id pk is also added automatically.
Your model names should be singular.
class Result(models.Model):
device = models.ForeignKey(Device, null=True, on_delete=models.SET_NULL)
res_key = models.SlugField(max_length=80, verbose_name="Message unique key", unique=True)
read_date = models.DateTimeField(verbose_name="Datetime of vals readings")
unit = models.ForeignKey(ModbusDevice, null=True, on_delete=models.SET_NULL)
def __str__(self):
return self.device
class Meta:
indexes = [
models.Index(fields=['device', 'unit']),
]
class VarsResult(models.Model):
result = models.ForeignKey(Result, related_name="mainres", on_delete=models.CASCADE)
modbus_variable = models.ForeignKey(ModbusVariable, null=True, on_delete=models.SET_NULL)
var_val = models.CharField(max_length=400, blank=True)
var_hash = models.CharField(max_length=400)
def __str__(self):
return self.var_hash
class Meta:
indexes = [
models.Index(fields=['result', 'modbus_variable']),
]
Now if you pass Result instance to ResultsSerializer it will also return all its mainres.
class ResultsSerializer(serializers.ModelSerializer):
mainres = VarsResultsSerializer(many=True, read_only=True)
class Meta:
model = Results
fields = ['id', 'device', 'res_key', 'read_date', 'unit', 'mainres']
class VarsResultsSerializer(serializers.ModelSerializer):
class Meta:
model = VarsResults
fields = ['id', 'id_res', 'var_id', 'var_val', 'var_hash']
You can take it a step further (I'm not sure what exactly do you need) and return all results from a single Device.
class DeviceSerializer(serializers.ModelSerializer):
results = ResultSerializer(many=True, read_only=True, source='result_set')
class Meta:
model = Device
fields = ['id', 'results']
Depending on your needs, read about select_related and prefetch_related.
If you want to use view for Result, you should Result.objects.prefetch_related('mainres').all()

Answer 2

Use django-rest-framework serializer to do it.
https://www.django-rest-framework.org/api-guide/serializers/
Read the doc, make some tests and your life will be simplify with django ;)
Change your serializer with :
class VarsResultsSerializer(serializers.ModelSerializer):
id_res = ResultsSerializer(read_only=True)
class Meta:
model = VarsResults
fields = ['id', 'id_res', 'var_id', 'var_val', 'var_hash']