How to write a query based on multiple tables? - django

Question

I want the details of lender whose state,distrtict,religion,profession equals to borrowers details i.e;(state,distrtict,religion,profession)
This is borrowers models.py
class Borrower(models.Model):
district = models.TextField(blank=True)
state = models.TextField(blank=True)
profession = models.TextField(blank=True)
religion = models.TextField(blank=True)
This is Lenders models.py
class LenderStateDistrict(models.Model):
lenderId = models.CharField(max_length=5)
state = models.CharField(max_length=50,**optional)
district = models.CharField(max_length=50,**optional)
class LenderReligion(models.Model):
lenderId = models.CharField(max_length=5)
religion = models.CharField(max_length=50, **optional)
class LenderMultipleProfessions(models.Model):
lenderId = models.CharField(max_length=5)
profession = models.CharField(max_length=50,**optional)
views.py
#api_view(['GET'])
def xyz(request):
borrower1= Borrower.objects.get(id =1)
city = borrower1.district
state = borrower1.state
profession = borrower1.profession
religion = borrower1.religion
I got every requirement for borrower and then how to query based on the three tables i.e; LenderStateDistrict,LenderReligion,LenderMultipleProfessions,if the borrowers district,state,religion,profession equals to the lenders then it should give the details how to query it?

Answer 1

There's a fundamental problem with your models. They are not related to each other. The power of Relational Database Management Systems lies in making relationships!
Django offers ways to define the three most common types of database
relationships: many-to-one, many-to-many and one-to-one.
https://docs.djangoproject.com/en/1.10/topics/db/models/#relationships
At the very least you need to create a foreign key between your borrow and the lender. But it may need to be a ManyToMany relationship if users can borrows from more than one lender

Answer 2

As #e4c5 mentioned that there is a problem with your models, try to relate your models with each other so that writing queries become easier.
Try to implement this way:
class District(models.Model):
field1 = models.CharField(max_length=255)
field2 = models.CharField(max_length=255)
class Religion(models.Model):
field1 = models.CharField(max_length=255)
field2 = models.CharField(max_length=255)
class Profession(models.Model):
field1 = models.CharField(max_length=255)
field2 = models.CharField(max_length=255)
This should be your basic models according to your question, and then you can reference these models in your Lender and Borrower tables, this way:
class Lender(models.Model):
district = models.ForeignKey(District, related_name="lender_district")
profession = models.ForeignKey(Profession, related_name="lender_profession")
religion = models.ForeignKey(Religion, related_name="lender_region")
class Borrower(models.Model):
district = models.ForeignKey(District, related_name="borrower_district")
profession = models.ForeignKey(Profession, related_name="borrower_profession")
religion = models.ForeignKey(Religion, related_name="borrower_region")
This way you can achieve that query that you want. Suppose you want to access the details of Borrower and Lender who belongs to district where field1 = "xyz", for that you have to simply write:
lenders = Lender.objects.filter(district__field1="xyz")
borrowers = Borrower.objects.filter(district__field1="xyz")
And further simple way is:
district = District.objects.get(field1="xyz") # get district
lenders = Lender.objects.filter(district=district) # Get Lenders
borrowers = Borrower.objects.filter(district=district) # Get Borrowers
You can implement ManyToMany relations too if lender and Borrower has more than one District, Religion or Profession.