maestral.utils.orm

A basic object relational mapper for SQLite.

This is a very simple ORM implementation which contains only functionality needed by Maestral. Many operations will still require explicit SQL statements. This module is no alternative to fully featured ORMs such as sqlalchemy but may be useful when system memory is constrained.

class maestral.utils.orm.SqlType[source]

Bases: object

Base class to represent Python types in SQLite table

sql_type = 'TEXT'

py_type: alias of str

static sql_to_py(value)[source]: Converts the return value from sqlite3 to the target Python type.

static py_to_sql(value)[source]: Converts a Python value to a type accepted by sqlite3.

class maestral.utils.orm.SqlString[source]

Bases: maestral.utils.orm.SqlType

Class to represent Python strings in SQLite table

sql_type = 'TEXT'

py_type: alias of str

class maestral.utils.orm.SqlInt[source]

Bases: maestral.utils.orm.SqlType

Class to represent Python integers in SQLite table

sql_type = 'INTEGER'

py_type: alias of int

class maestral.utils.orm.SqlFloat[source]

Bases: maestral.utils.orm.SqlType

Class to represent Python floats in SQLite table

sql_type = 'REAL'

py_type: alias of float

class maestral.utils.orm.SqlPath[source]

Bases: maestral.utils.orm.SqlType

Class to represent Python paths in SQLite table

This class contains special handling for strings with surrogate escape characters which can appear in badly encoded file names.

sql_type = 'TEXT'

py_type: alias of str

class maestral.utils.orm.SqlEnum(enum)[source]

Bases: maestral.utils.orm.SqlType

Class to represent Python enums in SQLite table

Parameters: enum (Iterable[enum.Enum]) –
Return type: None

sql_type = 'TEXT'

py_type: alias of enum.Enum

sql_to_py(value)[source]

Parameters: value (Optional[str]) –
Return type: Optional[enum.Enum]

static py_to_sql(value)[source]

Parameters: value (Optional[enum.Enum]) –
Return type: Optional[str]

class maestral.utils.orm.Column(type, nullable=True, unique=False, primary_key=False, index=False, default=None)[source]

Bases: property

Represents a column in a database table.

Parameters

type (maestral.utils.orm.SqlType) – Column type in database table. Python types which don’t have SQLite equivalents, such as enum.Enum, will be converted appropriately.
nullable (bool) – When set to False, will cause the “NOT NULL” phrase to be added when generating the column.
unique (bool) – If True, sets a unique constraint on the column.
primary_key (bool) – If True, marks this column as a primary key column. Currently, only a single primary key column is supported.
index (bool) – If True, create an index on this column.
default (Union[str, int, float, enum.Enum, None, Type[NoDefault]]) – Default value for the column. Set to NoDefault if no default value should be used. Note than None / NULL is a valid default for an SQLite column.

render_constraints()[source]

Returns a string with constraints for the SQLite column definition.

Return type: str

render_properties()[source]

Returns a string with properties for the SQLite column definition.

Return type: str

render_column()[source]

Returns a string with the full SQLite column definition.

Return type: str

py_to_sql(value)[source]

Converts a Python value to a value which can be stored in the database column.

Parameters: value (Optional[Union[str, int, float, enum.Enum]]) – Native Python value.
Returns: Converted Python value to store in database. Will only return str, int, float or None.
Return type: Optional[Union[str, int, float]]

sql_to_py(value)[source]

Converts a database column value to the original Python type.

Parameters: value (Optional[Union[str, int, float]]) – Value from database column. Only accepts str, int, float or None.
Returns: Converted Python value.
Return type: Optional[Union[str, int, float, enum.Enum]]

class maestral.utils.orm.NoDefault[source]

Bases: object

Class to denote the absence of a default value.

This is distinct from None which may be a valid default.

class maestral.utils.orm.Database(*args, **kwargs)[source]

Bases: object

Proxy class to access sqlite3.connect method.

Return type: None

property connection: sqlite3.Connection: Returns an existing SQL connection or creates a new one.

close()[source]

Closes the SQL connection.

Return type: None

commit()[source]

Commits SQL changes.

Return type: None

execute(sql, *args)[source]

Creates a cursor and executes the given SQL statement.

Parameters

sql (str) – SQL statement to execute.
args – Parameters to substitute for placeholders in SQL statement.

Returns

The created cursor.

Return type

sqlite3.Cursor

executescript(script)[source]

Creates a cursor and executes the given SQL script.

Parameters: script (str) – SQL script to execute.
Returns: The created cursor.
Return type: None

class maestral.utils.orm.Manager(db, model)[source]

Bases: object

A data mapper interface for a table model.

Creates the table as defined in the model if it doesn’t already exist. Keeps a cache of weak references to all retrieved and created rows to speed up queries. The cache should be cleared manually changes where made to the table from outside this manager.

Parameters

db (maestral.utils.orm.Database) – Database to use.
model (Type[Model]) – Model for database table.

Return type

None

create_table()[source]

Creates the table as defined by the model.

Return type: None

clear_cache()[source]

Clears our cache.

Return type: None

get_primary_key(obj)[source]

Returns the primary key for a model object / row in the table.

Parameters: obj (maestral.utils.orm.Model) – Model instance which represents the row.
Returns: Primary key for row.
Return type: Optional[Union[str, int, float]]

all()[source]

Get all model objects / rows from database in a single query.

Returns: List of model objects.
Return type: List[maestral.utils.orm.Model]

iter_all(size=1000)[source]

Get all model objects / rows from database in multiple queries.

Parameters: size (int) – Number of rows to fetch in each query.
Returns: Iterator over lists of model objects.
Return type: Generator[List[maestral.utils.orm.Model], Any, None]

create(**kwargs)[source]

Create a model object from SQL column values

Parameters: kwargs – Column values.
Returns: Model object.
Return type: maestral.utils.orm.Model

delete(obj)[source]

Delete a model object / row from database.

Parameters: obj (maestral.utils.orm.Model) – Object / row to delete.
Return type: None

delete_primary_key(primary_key)[source]

Delete a model object / row from database by primary key.

Parameters: primary_key (Optional[Union[str, int, float, enum.Enum]]) – Primary key for row.
Return type: None

get(primary_key)[source]

Gets a model object from database by its primary key. This will return a cached value if available and None if no row with the primary key exists.

Parameters: primary_key (Optional[Union[str, int, float, enum.Enum]]) – Primary key for row.
Returns: Model object representing the row.
Return type: Optional[maestral.utils.orm.Model]

has(primary_key)[source]

Checks if a model object exists in database by its primary key

Parameters: primary_key (Optional[Union[str, int, float, enum.Enum]]) – The primary key.
Returns: Whether the corresponding row exists in the table.
Return type: bool

save(obj)[source]

Saves a model object to the database table. If the primary key is None, a new primary key will be generated by SQLite on inserting the row. This key will be retrieved and stored in the primary key property of the object.

Parameters: obj (maestral.utils.orm.Model) – Model object to save.
Returns: Saved model object.
Return type: maestral.utils.orm.Model

update(obj)[source]

Updates the database table from a model object.

Parameters: obj (maestral.utils.orm.Model) – The object to update.
Return type: None

query_to_objects(sql, *args)[source]

Performs the given SQL query and converts any returned rows to model objects.

Parameters

sql (str) – SQL statement to execute.
args – Parameters to substitute for placeholders in SQL statement.

Returns

List of model objects from the query.

Return type

List[maestral.utils.orm.Model]

count()[source]

Returns the number of rows in the table.

Return type: int

class maestral.utils.orm.Model(**kwargs)[source]

Bases: object

Abstract object model to represent an SQL table.

Instances of this class are model objects which correspond to rows in the database table.

To define a table, subclass this Model and define Column`s as class properties. Override the ``__tablename__` attribute with the actual table name.

Initialise with keyword arguments corresponding to column names and values.

Parameters: kwargs – Keyword arguments assigning values to table columns.
Return type: None