UpdateRequest¶

An UpdateRequest is used to perform an update_item transaction with DynamoDB.

https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_UpdateItem.html

class cerami.request.UpdateRequest(client, tablename='', request_attributes=None, reconstructor=None)¶

A class to perform the update request

__init__(client, tablename='', request_attributes=None, reconstructor=None)¶

constructor for base request

Parameters

client – A boto3.client('dynamodb')
tablename – the name of the table to perform the request on
request_attributes –
a dict of SearchAttribute objects whose keys represent options that can be passed to client upon execution For example, it may include a FilterExpression key whose value is a SearchAttribute that resolves to a string of filters. This is typically None but can be used to manually build requests:
```
Parent.scan.filter(Parent.name == 'Mom').project(Parent.name)
# The search_attributes can be manually specified
ScanRequest(client=client, tablename='parents', search_attributes={
    'FilterExpression': SearchAttribute('name = Mom'),
    'ProjectionExpression': SearchAttribute('name'),
})
```
reconstructor – a Reconstructor object

add(datatype, value)¶

Add an ADD statement to the UpdateExpression

Amazon recommends only using with numbers and sets

The UpdateExpression is a comma separated list of instructions to perform on the table. ADD can be used to change the value of the Number or add to a Set.

Parameters

datatype – a DynamoDataType object to change
value – the value to change the datatype For Numbers the value should be a number, it can be negative to subtract For Sets, the value should be an array

Returns

the caller of the method. This allows for chaining

For example:

Person.update.key(Person.email == "test@test.com").add(Person.age, 10).build()
{
    "TableName": "people",
    "ReturnValues": "ALL_NEW",
    "Key": {
        "email": {
            "S": "test@test.com"
        }
    },
    "UpdateExpression": "ADD #__age  :_age_dzszf",
    "ExpressionAttributeNames": {
        "#__age": "age"
    },
    "ExpressionAttributeValues": {
        ":_age_dzszf": {
            "N": "10"
        }
    }
}

add_attribute(attr_class, name, value)¶

add a search attribute to a to the request_attributes dict

All search attributes must be unique keys. When the key already exists, it will update that value by calling add(). Depending on the attr_class, this can overwrite, append, change the value of the existing search attribute.

Parameters

attr_class – a SearchAttribute class
name – the name of the attribute
value – the value that will be added to the SearchAttribute

For example:

Person.scan.limit(10)
# or ...
Person.scan.add_attribute(SearchAttribute, 'Limit', 10)

build()¶

build the dict used by dynamodb

Returns: a dict whose keys matching the keys of the request_attributes and whose values are string versions of each attribute

For example:

User.scan.filter(User.email == 'test@test.com').build()
{
    "TableName": "Users",
    "FilterExpression": "#__email = :_email_dpxqm",
    "ExpressionAttributeNames": {
        "#__email": "email"
    },
    "ExpressionAttributeValues": {
        ":_email_dpxqm": {
            "S": "test@test.com"
        }
    }
}

delete(datatype, value)¶

Add a DELETE statement to the UpdateExpression

The UpdateExpression is a comma separated list of instructions to perform on the table. DELETE can be used to remove one or more elements from a Set only.

Parameters

datatype – a Set DynamoDatatype object
value – an array of values to remove from the set.

Returns

the caller of the method. This allows for chaining

For example:

Person.update \
    .key(Person.email == "test@test.com") \
    .delete(Person.tags, ["cool", "awesome"]) \
    .build()
{
    "TableName": "people",
    "ReturnValues": "ALL_NEW",
    "Key": {
        "name": {
            "S": "test@test.com"
        }
    },
    "UpdateExpression": "DELETE #__tags  :_tags_bttwj",
    "ExpressionAttributeNames": {
        "#__tags": "tags"
    },
    "ExpressionAttributeValues": {
        ":_tags_bttwj": {
            "SS": [
                "cool",
                "awesome"
            ]
        }
    }
}

execute()¶

perform the update_item request

Returns: a SaveResponse object built from the update_item response

For example:

Person.update \
    .key(Person.email == 'test@test.com') \
    .set(Person.name, 'Mommy') \
    .execute()

key(*expressions)¶

return a new Request setup with the Key attribute

Adds the Key to the request_attributes dict

Parameters: *expressions – a list of BaseExpressions
Returns: the caller of the method. This allows for chaning

For example:

Person.get.key(Person.email == 'test@test.com').build()
{
    "TableName": "people",
    "Key": {
        "email": {
            "S": "test@test.com"
        }
    }
}

remove(*datatypes)¶

Add a REMOVE statement to the UpdateExpression

The UpdateExpression is a comma separated list of instructions to perform on the table. REMOVE will delete the specified datatypes from the record. REMOVE can also be used to remove elements from a List datatype when used with List.index()

Parameters: *datatypes – a list of DynamoDataType objects
Returns: the caller of the method. This allows for chaining

For example:

Person.update \
    .key(Person.email == "test@test.com") \
    .remove(Person.name) \
    .build()
{
    "TableName": "people",
    "ReturnValues": "ALL_NEW",
    "Key": {
        "email": {
            "S": "test@test.com"
        }
    },
    "UpdateExpression": "REMOVE #__name  :_name_butcw",
    "ExpressionAttributeNames": {
        "#__name": "name"
    }
}

returns(value)¶

return the Request setup with ReturnValues attribute

Adds the ReturnValues to the request attributes dict

Parameters: value – NONE | ALL_OLD | UPDATED_OLD | ALL_NEW | UPDATED_NEW
Returns: the caller of the method. This allows for chaining

For example:

from cerami.request.return_values import UPDATED_NEW
Person.update \
    .key(Person.email == 'test@test.com') \
    .set(Person.name, 'new name') \
    .returns(UPDATED_NEW) \
    .build()
{
    "TableName": "people",
    "ReturnValues": "UPDATED_NEW",
    "Key": {
        "email": {
            "S": "test@test.com"
        }
    },
    "UpdateExpression": "SET #__name = :_name_zhvzz",
    "ExpressionAttributeNames": {
        "#__name": "name"
    },
    "ExpressionAttributeValues": {
        ":_name_zhvzz": {
            "S": "new name"
        }
    }
}

set(expression_or_datatype, value=None)¶

Add a SET statement to the UpdateExpression

The UpdateExpression is a comma separated list of instructions to perform on the table. SET will change the value or put the value if it does not exist.

Sorry, i dont know how to do method overloading in python yet, so were stuck with this garbage..

Parameters

datatype_or_expresion – a DynamoDataType or BaseExpresion object to change
value – the value to change the datatype

Returns

the caller of the method. This allows for chaining

For example:

Person.update \
    .key(Person.email == "test@test.com") \
    .set(Person.name, "Zac") \
    .execute()

Person.update \
    .key(Person.email == "test@test.com") \
    .set(Person.age.add(10))
    .execute()

update_expression(action, expression)¶

return a Request setup with the update expression attributes

Adds the UpdateExpression, ExpressionAttributeNames and ExpressionAttributeValues to the request_attributes dict

Parameters

action – ADD | SET | DELETE | UPDATE
expression – a BaseExpression object

Returns

the caller of the method. This allows for chaining