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pythondjangodjango-orm
Holly
Holly

Reputation: 1217

Django bulk update with string replace

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_field, 'old text', 'new text');

With that query, I expect old text and old text more text to be replaced with new text and new text more text respectively, for all the entries in the string_field column.

Bulk update() seems promising, but doesn't allow me to modify only part of the field, and F() expressions only implement numeric changes, not string replace. I also looked at using raw queries to run the above SQL, but that seems like a sideways hack (especially since F() exists to do the same functionality on numbers), and I couldn't get them to actually execute.

I ended up with this, but it seems a shame to execute all the extra queries when I know there's a one line SQL statement to do it.

for entry in ExampleModel.objects.all():
    entry.string_field = entry.string_field.replace('old text', 'new text', 1)
    entry.save()

Does this feature not exist in Django's ORM for strings yet? Is there something I overlooked in the docs?

Related SO questions:

Upvotes: 30

Views: 15775

Answers (5)

pymen
pymen

Reputation: 6539

Use replace_field_substring(YourModel, "your_field", "value_from", "value_to")

from django.db.models import F, Value, QuerySet
from django.db.models.functions import Replace

def replace_field_substring(model_or_qs, field, value_from, value_to):
    """Generates ORM partial replace, which can be used in Django ORM data migrations,
    for example for partial replace tbl.cont from="twitter.com" to="x.com" will give you
    UPDATE tbl SET cont = REPLACE(cont, 'twitter.com', 'x.com') WHERE cont LIKE '%twitter.com%';
    """
    qs = model_or_qs if isinstance(model_or_qs, QuerySet) else model_or_qs.objects.all()
    replacement_expression = Replace(F(field), Value(value_from), Value(value_to))
    qs.update(**{field: replacement_expression})

Upvotes: 0

Dave Lawrence
Dave Lawrence

Reputation: 1236

New in Django 2.1 - Replace database function

Your example can now be expressed most easily via:

ExampleModel.objects.update(
    string_field=Replace('string_field', Value('old_text'), Value('new_text'))
)

Upvotes: 5

Nhu Trinh
Nhu Trinh

Reputation: 13956

Tested with django 1.9

from django.db.models import F, Func, Value

ExampleModel.objects.filter(<condition>).update(
    string_field=Func(
        F('string_field'),
        Value('old text'), Value('new text'),
        function='replace',
    )
)

UPDATE Django 2.1 https://docs.djangoproject.com/en/2.2/ref/models/database-functions/#replace

from django.db.models import Value
from django.db.models.functions import Replace

ExampleModel.objects.filter(<condition>).update(
    string_field=Replace('string_field', Value('old text'), Value('new text'))
)

Upvotes: 42

Alhamsya Bintang Dyasta
Alhamsya Bintang Dyasta

Reputation: 71

Django 2.2 support bulk update, can you using function that one.

Check this one : https://docs.djangoproject.com/en/2.2/ref/models/querysets/#django.db.models.query.QuerySet.bulk_create

Upvotes: -1

Andrew Magee
Andrew Magee

Reputation: 6684

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.

Upvotes: 5

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