Dynamic logic query builder in Django

Question

I'm have 2 table in DB:

class Param(models.Model):
    s_name = models.CharField(max_length=200)
    n_name = models.CharField(max_length=200)

class ParamValue(models.Model):
    param = models.ForeignKey(Param)
    value = models.IntegerField()
    created = models.DateTimeField(default=datetime.now, blank=True)

I wanted to create dynamic constructor. Is there any library or method for create dynamic logic filter like as Apache Lucene or Solr? I mean something like this:

dyn_filter = parse("(value < 200 AND value__s_name == 'pressure') 
    OR (value > 10 AND value__s_name == 'depth')")
result = ParamValue.objects.filter(dyn_filer)

I want generate filter, maybe. Now I'm look at whoosh (whoosh.readthedocs.io/en/latest/querylang.html) — Yuriy Bosov
– Yuriy Bosov, Commented Sep 20, 2017 at 23:30
Do you also want a parser or do you only want the ORM to execute the equivalent query? — Bernardo Duarte
– Bernardo Duarte, Commented Sep 20, 2017 at 23:42
I think that I need parser, because query string ("(value < 200 AND ....)") should be stored in database — Yuriy Bosov
– Yuriy Bosov, Commented Sep 20, 2017 at 23:50

Bernardo Duarte · Accepted Answer · 2017-09-20 23:49:17Z

3

Django ORM has the Q objects which allows you to write the logic operation OR with the Queryset parameters.

The bellow example does exactly what your text ("(value < 200 AND value__s_name == 'pressure') OR (value > 10 AND value__s_name == 'depth')") asks for:

from django.db.models import Q
ParamValue.objects.filter(
    Q(value__lt=200, param__s_name='pressure') | Q(value__gt=10, param__s_name='depth')
)

answered Sep 20, 2017 at 23:49

Bernardo Duarte

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Comments

alfredo138923 · Accepted Answer · 2017-09-21 02:08:24Z

2

Check the library DjangoQL. It supports logical operators, comparison operators, parenthesis, table joins, etc.

from django.db import models

from djangoql.queryset import DjangoQLQuerySet


class Book(models.Model):
    name = models.CharField(max_length=255)
    author = models.ForeignKey('auth.User')

    objects = DjangoQLQuerySet.as_manager()

With the example above you can perform search like this:

qs = Book.objects.djangoql(
    'name ~ "war" and author.last_name = "Tolstoy"'
)

And DjangoQL will execute the equivalent Django queryset.

edited Sep 21, 2017 at 2:08

answered Sep 21, 2017 at 1:56

alfredo138923

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1 Comment

Yuriy Bosov Over a year ago

It's PERFECT! Thanks a lot!

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