djblets.db.fields.base64_field¶

Field for storing data as Base64-encoded values.

See Base64Field for the main field type and usage instructions.

exception Base64TypeError(value)¶

Bases: TypeError

Error indicating an invalid value type was provided for the field.

__init__(value)¶

Initialize the error.

Parameters:

value (object) – The invalid value that was passed.

class Base64DecodedValue¶

Bases: bytes

An identifiable wrapper around byte string values for Base64Field.

This wraps any values coming from Base64Field, helping make a distinction between arbitrary strings and decoded strings from the database. It helps prevent double-encoding or double-decoding of data.

class Base64FieldCreator(field)¶

Bases: object

Property-like class used to store/retrieve Base64 values.

This works much like a property, and takes care of encoding strings for storage and decoding them on retrieval. It’s set internally by Base64Field in place of the normal field attribute.

__init__(field)¶

Initialize the creator.

Parameters:

field (Base64Field) – The field owning this object.

__set__(obj, value)¶

Set a new value in the field.

If this is a Base64DecodedValue, or the model is new and hasn’t yet been persisted to the database, the value will be encoded and stored. Otherwise, if it’s a standard string value or the model is not new, it’s assumed that this is encoded data for storage, and will be stored directly.

Parameters:

• obj (django.db.models.Model) – The model owning the field.

• value (object) – The value being set. This must be a valid string value or Base64DecodedValue.

Raises:

Base64TypeError – The type of value provided could not be set.

__get__(obj, *args, **kwargs)¶

Return a decoded value from the field.

Parameters:

• obj (django.db.models.Model) – The model owning the field.

• *args (tuple) – Unused positional arguments.

• **kwargs (dict) – Unused keyword arguments.

Returns:

The decoded value from the field. If no value has yet been stored, this will return None instead.

Return type:

Base64DecodedValue

Raises:

• AttributeError –

• A –

class Base64Field(*args, db_collation=None, **kwargs)¶

Bases: TextField

A text field for storing Base64-encoded values.

This is used to store data (such as binary data or encoding-sensitive data) to the database in a Base64 encoding. This is useful if you’re dealing with unknown encodings and must guarantee that no modifications to the text occurs and that you can read/write the data in any database with any encoding.

When accessing this field on an instance of a model, a Base64DecodedValue will be returned consisting of the decoded data. This is a byte string, and can be treated as such. If set back into the field, it will be re-encoded and stored.

When writing to the field, the behavior changes based on the type of value and the state of the model:

• If the model instance is new (has not yet been saved in the database), any string set will be encoded. This allows the value to be passed during a create() call.

• If the model is not new, any string that’s set will be assumed to be encoded by the caller.

• Passing a Base64DecodedValue byte string will always cause the stored data to be encoded.

The field also adds a get_fieldname_base64() method to the class, which returns the raw Base64 encoded content from the database.

contribute_to_class(cls, name)¶

Set attributes on a new model class.

This is called when constructing a model class making use of this field. It sets the field’s attribute to a Base64FieldCreator and adds a get_fieldname_base64() method to the class.

Parameters:

• cls (type) – The class to add the arguments to.

• name (str) – The name of the field.

get_prep_value(value)¶

Return a value prepared for the field.

This prepares the value for use in database operations (saving or querying). It will convert the value into a Unicode Base64-encoded string.

Parameters:

value (object) – The value to prepare. This is expected to be a string or a Base64DecodedValue. If the latter, it will be encoded.

Returns:

The resulting value.

Return type:

unicode

Raises:

Base64TypeError – The type of value provided could not be prepared for writing.

to_python(value)¶

Return a Python representation of a value for the field.

This will decode the value (if not already decoded) and return it.

Parameters:

value (object) – The value to return a decoded value for.

Returns:

The decoded version of the provided value.

Return type:

Base64DecodedValue

Raises:

Base64TypeError – The type of value provided could not be prepared for writing.

value_to_string(obj)¶

Return a string representation of the value from a model.

The returned value will be a Base64-encoded string value.

Parameters:

obj (django.db.models.Model) – The model instance owning the field and value.

Returns:

The Base64-encoded string for the stored value.

Return type:

str