Snippet

Custom Database Expression Wrappers for Binary Vault Hashes

Subclassing Django Expression allows building custom DB-level expressions that compile into raw SQL functions yielding specialized binary datatypes.

snippet.py

python

from django.db.models import Expression, BinaryField
 
class SHA256DigestExpression(Expression):
    def __init__(self, expression):
        super().__init__(output_field=BinaryField())
        self.expression = expression
 
    def as_sql(self, compiler, connection):
        sql, params = compiler.compile(self.expression)
        return f"digest({sql}, 'sha256')", params
 
    def get_source_expressions(self):
        return [self.expression]
 
    def set_source_expressions(self, exprs):
        self.expression = exprs[0]

django

Breakdown

class SHA256DigestExpression(Expression):

Inherits from Django Expression base class to define custom SQL generation logic.

def as_sql(self, compiler, connection):

Compiles inner expression arguments and formats raw database function SQL syntax.

super().__init__(output_field=BinaryField())

Specifies BinaryField as the return datatype for Django ORM type casting.

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Custom Database Expression Wrappers for Binary Vault Hashes

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