Update Operations

The UpdateItem DynamoDB operations allows you to create or modify attributes of an item using an update expression. See the official documentation for more details.

Suppose that you have defined a Thread Model for the examples below.

from pynamodb.models import Model
from pynamodb.attributes import (
    ListAttribute, UnicodeAttribute, UnicodeSetAttribute, NumberAttribute
)


class Thread(Model):
    class Meta:
        table_name = 'Thread'

    forum_name = UnicodeAttribute(hash_key=True)
    subjects = UnicodeSetAttribute(default=dict)
    views = NumberAttribute(default=0)
    notes = ListAttribute(default=list)

Update Expressions

PynamoDB supports creating update expressions from attributes using a mix of built-in operators and method calls. Any value provided will be serialized using the serializer defined for that attribute.

DynamoDB Action / Operator	PynamoDB Syntax	Example
SET	set( value )	Thread.views.set(10)
REMOVE	remove()	Thread.notes[0].remove()
ADD	add( value )	Thread.subjects.add({‘A New Subject’, ‘Another New Subject’})
DELETE	delete( value )	Thread.subjects.delete({‘An Old Subject’})
attr_or_value_1 + attr_or_value_2	attr_or_value_1 + attr_or_value_2	Thread.views + 5
attr_or_value_1 - attr_or_value_2	attr_or_value_1 - attr_or_value_2	5 - Thread.views
list_append( attr , value )	append( value )	Thread.notes.append([‘my last note’])
list_append( value , attr )	prepend( value )	Thread.notes.prepend([‘my first note’])
if_not_exists( attr, value )	attr | value	Thread.forum_name | ‘Default Forum Name’