Django FULL OUTER JOIN - django

Question

I have these three tables
class IdentificationAddress(models.Model):
id_ident_address = models.AutoField(primary_key=True)
ident = models.ForeignKey('Ident', models.DO_NOTHING, db_column='ident')
address = models.TextField()
time = models.DateTimeField()
class Meta:
managed = False
db_table = 'identification_address'
class IdentC(models.Model):
id_ident = models.AutoField(primary_key=True)
ident = models.TextField(unique=True)
name = models.TextField()
class Meta:
managed = False
db_table = 'ident_c'
class location(models.Model):
id_ident_loc = models.AutoField(primary_key=True)
ident = models.ForeignKey('IdentC', models.DO_NOTHING, db_column='ident')
loc_name = models.TextField()
class Meta:
managed = False
db_table = 'location
I want to get the last
address field (It could be zero) from IdentificationAddress model, the last _loc_name_ field (it matches at least one) from location model, name field (Only one) from IdentC model and ident field. The search is base on ident field.
I have been reading about many_to_many relationships and prefetch_related. But, they don't seem to be the best way to get these information.
If a use SQL syntax, this instruction does the job:
SELECT ident_c.name, ident_c.ident, identification_address.address, location.loc_name FROM identn_c FULL OUTER JOIN location ON ident_c.ident=location.ident FULL OUTER JOIN identification_address ON ident_c.ident=identification_address.ident;
or for this case
SELECT ident_c.name, ident_c.ident, identification_address.address, location.loc_name FROM identn_c LEFT JOIN location ON ident_c.ident=location.ident LEFT JOIN identification_address ON ident_c.ident=identification_address.ident;
Based on my little understanding of Django, JOIN instructions cannot be implemented. Hope I am wrong.

Answer 1

Django ORM take care of it if you set relationship between models.
for example,
models.py
class Aexample(models.Model):
name = models.CharField(max_length=20)
class Bexample(models.Model):
name = models.CharField(max_length=20)
fkexample = models.ForeignKey(Aexample)
shell
examplequery = Bexample.objects.filter(fkexample__name="hellothere")
SQL query
SELECT
"yourtable_bexample"."id",
"yourtable_bexample"."name",
"yourtable_bexample"."fkexample_id"
FROM "yourtable_bexample"
INNER JOIN "yourtable_aexample"
ON ("yourtable_bexample"."fkexample_id" = "yourtable_aexample"."id")
WHERE "yourtable_aexample"."name" = hellothere
you want to make query in Django like below
SELECT ident_c.name, ident_c.ident, identification_address.address, location.loc_name
FROM identn_c
LEFT JOIN location ON ident_c.ident=location.ident
LEFT JOIN identification_address ON ident_c.ident=identification_address.ident;
It means you want all rows from identn_c, right?. If you make proper relationship between your tables for your purpose, Django ORM takes care of it.
class IntentC(model.Model):
exampleA = models.ForeignKey(ExampleA)
exampleB = models.ForeignKey(ExampleB)
this command make query with JOIN Clause.
identn_instance = IdentC.objects.get(id=somenumber)
identn_instance.exampleA
identn_instance.exampleB
you can show every IntentC rows and relating rows in different tables.
for in in IntentC.objects.all(): #you can all rows in IntentC
print(in.exampleA.name)
#show name column in exampleA table
#JOIN ... ON intenctctable.example_id = exampleatable.id
print(in.exampleB.name) #show name column in exampleB table / JOIN ... ON