from marshmallow.fields import Field
from marshmallow.schema import Schema, SchemaMeta, SchemaOpts
import sqlalchemy as sa
from sqlalchemy.ext.declarative import DeclarativeMeta
from .convert import ModelConverter
from .exceptions import IncorrectSchemaTypeError
from .load_instance_mixin import LoadInstanceMixin
# This isn't really a field; it's a placeholder for the metaclass.
# This should be considered private API.
class SQLAlchemyAutoField(Field):
def __init__(self, *, column_name=None, model=None, table=None, field_kwargs):
super().__init__()
if model and table:
raise ValueError("Cannot pass both `model` and `table` options.")
self.column_name = column_name
self.model = model
self.table = table
self.field_kwargs = field_kwargs
def create_field(self, schema_opts, column_name, converter):
model = self.model or schema_opts.model
if model:
return converter.field_for(model, column_name, **self.field_kwargs)
else:
table = self.table if self.table is not None else schema_opts.table
column = getattr(table.columns, column_name)
return converter.column2field(column, **self.field_kwargs)
# This field should never be bound to a schema.
# If this method is called, it's probably because the schema is not a SQLAlchemySchema.
def _bind_to_schema(self, field_name, schema):
raise IncorrectSchemaTypeError(
f"Cannot bind SQLAlchemyAutoField. Make sure that {schema} is a SQLAlchemySchema or SQLAlchemyAutoSchema."
)
[docs]class SQLAlchemySchemaOpts(LoadInstanceMixin.Opts, SchemaOpts):
"""Options class for `SQLAlchemySchema`.
Adds the following options:
- ``model``: The SQLAlchemy model to generate the `Schema` from (mutually exclusive with ``table``).
- ``table``: The SQLAlchemy table to generate the `Schema` from (mutually exclusive with ``model``).
- ``load_instance``: Whether to load model instances.
- ``sqla_session``: SQLAlchemy session to be used for deserialization.
This is only needed when ``load_instance`` is `True`. You can also pass a session to the Schema's `load` method.
- ``transient``: Whether to load model instances in a transient state (effectively ignoring the session).
Only relevant when ``load_instance`` is `True`.
- ``model_converter``: `ModelConverter` class to use for converting the SQLAlchemy model to marshmallow fields.
"""
def __init__(self, meta, *args, **kwargs):
super().__init__(meta, *args, **kwargs)
self.model = getattr(meta, "model", None)
self.table = getattr(meta, "table", None)
if self.model is not None and self.table is not None:
raise ValueError("Cannot set both `model` and `table` options.")
self.model_converter = getattr(meta, "model_converter", ModelConverter)
[docs]class SQLAlchemyAutoSchemaOpts(SQLAlchemySchemaOpts):
"""Options class for `SQLAlchemyAutoSchema`.
Has the same options as `SQLAlchemySchemaOpts`, with the addition of:
- ``include_fk``: Whether to include foreign fields; defaults to `False`.
- ``include_relationships``: Whether to include relationships; defaults to `False`.
"""
def __init__(self, meta, *args, **kwargs):
super().__init__(meta, *args, **kwargs)
self.include_fk = getattr(meta, "include_fk", False)
self.include_relationships = getattr(meta, "include_relationships", False)
if self.table is not None and self.include_relationships:
raise ValueError("Cannot set `table` and `include_relationships = True`.")
class SQLAlchemySchemaMeta(SchemaMeta):
@classmethod
def get_declared_fields(mcs, klass, cls_fields, inherited_fields, dict_cls):
opts = klass.opts
Converter = opts.model_converter
converter = Converter(schema_cls=klass)
fields = super().get_declared_fields(
klass, cls_fields, inherited_fields, dict_cls
)
fields.update(mcs.get_declared_sqla_fields(fields, converter, opts, dict_cls))
fields.update(mcs.get_auto_fields(fields, converter, opts, dict_cls))
return fields
@classmethod
def get_declared_sqla_fields(mcs, base_fields, converter, opts, dict_cls):
return {}
@classmethod
def get_auto_fields(mcs, fields, converter, opts, dict_cls):
return dict_cls(
{
field_name: field.create_field(
opts, field.column_name or field_name, converter
)
for field_name, field in fields.items()
if isinstance(field, SQLAlchemyAutoField)
and field_name not in opts.exclude
}
)
class SQLAlchemyAutoSchemaMeta(SQLAlchemySchemaMeta):
@classmethod
def get_declared_sqla_fields(cls, base_fields, converter, opts, dict_cls):
fields = dict_cls()
if opts.table is not None:
fields.update(
converter.fields_for_table(
opts.table,
fields=opts.fields,
exclude=opts.exclude,
include_fk=opts.include_fk,
base_fields=base_fields,
dict_cls=dict_cls,
)
)
elif opts.model is not None:
fields.update(
converter.fields_for_model(
opts.model,
fields=opts.fields,
exclude=opts.exclude,
include_fk=opts.include_fk,
include_relationships=opts.include_relationships,
base_fields=base_fields,
dict_cls=dict_cls,
)
)
return fields
[docs]class SQLAlchemySchema(
LoadInstanceMixin.Schema, Schema, metaclass=SQLAlchemySchemaMeta
):
"""Schema for a SQLAlchemy model or table.
Use together with `auto_field` to generate fields from columns.
Example: ::
from marshmallow_sqlalchemy import SQLAlchemySchema, auto_field
from mymodels import User
class UserSchema(SQLAlchemySchema):
class Meta:
model = User
id = auto_field()
created_at = auto_field(dump_only=True)
name = auto_field()
"""
OPTIONS_CLASS = SQLAlchemySchemaOpts
[docs]class SQLAlchemyAutoSchema(SQLAlchemySchema, metaclass=SQLAlchemyAutoSchemaMeta):
"""Schema that automatically generates fields from the columns of
a SQLAlchemy model or table.
Example: ::
from marshmallow_sqlalchemy import SQLAlchemyAutoSchema, auto_field
from mymodels import User
class UserSchema(SQLAlchemyAutoSchema):
class Meta:
model = User
# OR
# table = User.__table__
created_at = auto_field(dump_only=True)
"""
OPTIONS_CLASS = SQLAlchemyAutoSchemaOpts
[docs]def auto_field(
column_name: str = None,
*,
model: DeclarativeMeta = None,
table: sa.Table = None,
**kwargs,
):
"""Mark a field to autogenerate from a model or table.
:param column_name: Name of the column to generate the field from.
If ``None``, matches the field name. If ``attribute`` is unspecified,
``attribute`` will be set to the same value as ``column_name``.
:param model: Model to generate the field from.
If ``None``, uses ``model`` specified on ``class Meta``.
:param table: Table to generate the field from.
If ``None``, uses ``table`` specified on ``class Meta``.
:param kwargs: Field argument overrides.
"""
if column_name is not None:
kwargs.setdefault("attribute", column_name)
return SQLAlchemyAutoField(
column_name=column_name, model=model, table=table, field_kwargs=kwargs
)
