Django bulk update with string replace

Question

I am trying to update and modify a string field Django\'s ORM. The equivalent SQL to do this is:

UPDATE example_table SET string_field = REPLACE(string_fiel         


        

Answer 1

You could make your own F-like object to represent the string replacing in SQL. Here is a proof of concept:

from django.db.models.expressions import ExpressionNode

class StringReplaceF(ExpressionNode):
    def __init__(self, field, replace_from, replace_to):
        self.field = field
        self.replace_from = replace_from
        self.replace_to = replace_to
        super(StringReplaceF, self).__init__()

    def evaluate(self, evaluator, qn, connection):
        return (
            "REPLACE({}, %s, %s)".format(self.field),
            (self.replace_from, self.replace_to)
        )

 >>> f = StringReplaceF('string_field', 'old text', 'new text')
 >>> ExampleModel.objects.update(string_field=f)

You'd need to do a bit more work with the class if you need it to behave nicely with other F objects, but then again, the existing F objects don't seem to work with strings anyway.