djorm-ext-expressions 0.5

Simple usage

Imagine some django model with postgresql integer array field. You need to find objects in the field containing a set of group numbers.

NOTE: array field is part of django orm extensions package and is located on djorm-ext-pgarray submodule.

Example model definition

from django.db import models
from djorm_expressions.models import ExpressionManager
from .somefiels import ArrayField

class Register(models.Model):
    name = models.CharField(max_length=200)
    points = ArrayField(dbtype="int")

    objects = ExpressionManager()

With this model definition, we can do this searches:

from djorm_expressions.base import SqlExpression, AND, OR

# search all register items that points field contains [2,3]

qs = Register.manager.where(
    SqlExpression("points", "@>", [2,3])
)

# search all register items that points fields contains [2,3] or [5,6]

expression = OR(
    SqlExpression("points", "@>", [2,3]),
    SqlExpression("points", "@>", [5,6]),
)

qs = Register.objects.where(expression)

Also, we can use functions to construct a expression:

from djorm_expressions.base import SqlFunction

class BitLength(SqlFunction):
    sql_function = "bit_length"

# search all registers items that bit_length(name) > 20.
qs = Register.objects.where(
    SqlExpression(BitLength("name"), ">", 20)
)

I finally can redefine the behavior “SqlExpression” and make it more “object oriented”:

class ArrayExpression(object):
    def __init__(self, field):
        self.field = field

    def contains(self, value):
        return SqlExpression(self.field, "@>", value)

    def overlap(self, value):
        return SqlExpression(self.field, "&&", value)

# search all register items that points field contains [2,3]
qs = Register.objects.where(
    ArrayExpression("points").contains([2,3])
)