django queryset annotate all field in childtable - django

Question

models.py
class Userinfo(models.Model):
useruid = models.BigAutoField(db_column='UserUID', primary_key=True)
useremail = models.CharField(
db_column='UserEmail', unique=True, max_length=100)
userpassword = models.CharField(db_column='UserPassword', max_length=128)
passwordsalt = models.CharField(db_column='PasswordSalt', max_length=128)
class Meta:
managed = False
db_table = 'userinfo'
class Postinfo(models.Model):
postuid = models.BigAutoField(db_column='PostUID',primary_key=True)
useruid = models.ForeignKey(
'Userinfo', db_column='UserUID', on_delete=models.CASCADE)
content = models.TextField(db_column='Content')
class Meta:
managed = False
db_table = 'postinfo'
if i get userlist and user's last post
i think use annotate
models.Userinfo.objects.all().annotate(lastpost="??").order_by("-useruid")
what values in "??"
like this form
[{userinfo1,"lastpost":{postinfofields}},{userinfo2,"lastpost":{postinfofields}},{userinfo3,"lastpost":{postinfofields}}]
can i this query not use forloop?
Serializer.py
class PostSerializer(serializers.ModelSerializer):
class Meta:
model = Postinfo
fields = ('postuid','content')
class UserSerializer(serializers.ModelSerializer):
lastpost = PostSerializer()
class Meta:
model = Userinfo
fields = ['useruid', 'useremail', 'lastpost']
view.py
userinfos = models.Userinfo.objects.all().order_by("-useruid")
result = UserSerializer(userinfos,many=True)
print(result.data)
raise Exception
Got AttributeError when attempting to get a value for field `lastpost` on serializer `UserSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `Userinfo` instance.
Original exception text was: 'Userinfo' object has no attribute 'lastpost'.
if i add read_only=True print this
[OrderedDict([('useuid', 1), ('useremail', 'test')]), OrderedDict([('useruid', 2), ('useremail', 'test2')])]

Answer 1

You can use model's property for this:
class Userinfo(models.Model):
useruid = models.BigAutoField(db_column='UserUID', primary_key=True)
useremail = models.CharField(
db_column='UserEmail', unique=True, max_length=100)
userpassword = models.CharField(db_column='UserPassword', max_length=128)
passwordsalt = models.CharField(db_column='PasswordSalt', max_length=128)
#property
def lastpost(self):
return self.postinfo_set.latest('postuid')
Now you dont need annotation, just use it for example in template like this:
{{ user.lastpost.content }}
UPD
To serialize property with ModelSerializer just add serializer's field 'lastpost':
class PostSerializer(serializers.ModelSerializer):
class Meta:
model = Postinfo
fields = ('postuid','content')
class UserSerializer(serializers.ModelSerializer):
lastpost = PostSerializer()
class Meta:
model = Userinfo
fields = ['useruid', 'useremail', 'lastpost']
UPD2
You can also implement logic directly on the serializer level, without model's property. Just use SerializerMethodField:
class UserSerializer(serializers.ModelSerializer):
lastpost = SerializerMethodField()
class Meta:
model = Userinfo
fields = ['useruid', 'useremail', 'lastpost']
def get_lastpos(self, obj):
last = obj.postinfo_set.latest('postuid')
serializer = PostSerializer(last)
return serializer.data