UniformList

class cerami.datatype.UniformList(datatype, default=None, column_name='')

A class to represent Lists of entirely the same datatype

The Base List class uses a Guesser to try and determine the datatype to use for the each item in the array. A UniformList does not need to guess, since the datatype is consistent and stored as an attribute

__init__(datatype, default=None, column_name='')

constructor for UniformList

Parameters

• datatype – Any DynamoDataType that each item in the List will be

• default – a default value for the column. It can be a value or function

• column_name – a string defining the name of the column on the table

append(array)

Build an expression to add the array to the end of the existing column data

It can only be used in SET UpdateExpressions.

Parameters

array – can be a list or single value to be appended. When it is a single value, it is automatically put inside its own array, before building the expression.

Returns

A ListAppendExpression

For example:

Person.update \
    .key(Person.email == "test@test.com")
    .set(Person.toys.append({"color": "red", "name": "car"})

between(greater_than, less_than)

Build a BetweenExpression

BetweenExpression can be used with the filter() on the model or as a KeyConditionExpression on the sort key of a query

Parameters

• greater_than – a value that the query is greater than or equal to

• less_than – a value that the query is less than or equal to

Returns

A BetweenExpression

For example:

Person.scan.filter(Person.age.between(10, 20))

build(val)

build the column value based on the val passed in

building is called automatically by the DynamoDataAttribute when the model is initialized. It will use the default value when present if the val passed in is None

Parameters

val – A value that will be used to build the attribute on the instance

Returns

The passed in val or the default when the default is set

in_(*values)

Build an InExpression

InExpressions can only be used with filter() on the model, it cannot be part of a KeyConditionExpression. The will filter for the table for values that match exactly any of the values passed in as arguments

Parameters

values – anything value to use to filter the table

Returns

An InExpression

For example:

Person.scan.filter(Person.name.in_("Mom", "Dad"))

index(idx)

build a duplicate datatype with the _index set to idx

When forming a Request that involves a specific item in the UniformList, that item can be specified using this index() method

Parameters

idx – a number for the index of the desired item in the list

Returns

A copy of the datatype with _index set

For example:

MyModel.scan.filter(MyModel.number_list.index(2) == 100).execute()

set_column_name(val)

Update the column_name of this instance

Parameters

value – a string for the new column name