Module pyracmon.select
This module exports types and functions used for SELECT
queries.
Main purpose is providing a type which contains information of selecting columns, i.e. which columns are selected and how they are rendered in the query. Using the same instance of the type in both of query genration and reading results enables consistent reconstruction of model objects.
In most cases, classes of this module should not be used directly.
The use of SelectMixin.select()
and read_row()
is sufficient way to benefit from this module.
Expand source code
"""
This module exports types and functions used for `SELECT` queries.
Main purpose is providing a type which contains information of selecting columns,
i.e. which columns are selected and how they are rendered in the query.
Using the same instance of the type in both of query genration and reading results enables consistent reconstruction of model objects.
In most cases, classes of this module should not be used directly.
The use of `SelectMixin.select` and `read_row` is sufficient way to benefit from this module.
"""
from collections.abc import Iterator
from typing import Any, Union, TypeVar, Generic, Optional, Literal, Protocol, cast, overload
from typing_extensions import Self
from .model import Model, Column
from .query import Q, Queryable
S = TypeVar('S')
M = TypeVar('M', bound=Model)
class AliasedColumn(Queryable[Any]): # type: ignore
"""
The representation of column and the alias of its belonging table.
The instance of this class works as `Q` 's attribute as well.
i.e. Condition on the column can be generated similarly to 'Q' via methods like `eq` .
```python
>>> c = AliasedColumn("t", "col")
>>> c.eq(3)
Condition: 't.col = $_' -- [3]
```
"""
def __init__(self, alias: str, column: Union[Column, str]) -> None:
#: Alias string.
self.alias = alias
#: Column name or schema.
self.column = column
def __hash__(self) -> int:
return hash(self.alias) + hash(self.column)
def __eq__(self, other: object) -> bool:
return isinstance(other, AliasedColumn) and self.alias == other.alias and self.column is other.column
def __str__(self) -> str:
return self.name
@property
def name(self) -> str:
"""
Aliased column name. If alias is empty, column name is returns as it is.
"""
if isinstance(self.column, Column):
return f"{self.alias}.{self.column.name}" if self.alias else self.column.name
else:
return f"{self.alias}.{self.column}" if self.alias else self.column
def __getattr__(self, key):
method = getattr(Q, key)
def invoke(value, *args, **kwargs):
kwargs.update({self.name: value})
return method(*args, **kwargs)
return invoke
class Aliased(Generic[M]):
"""
A wrapper of a model type with an alias for it.
"""
def __init__(self, alias: str, model: type[M]) -> None:
#: Alias string.
self.alias = alias
#: Model type.
self.model = model
def __getattr__(self, key: str) -> AliasedColumn:
try:
col = next(filter(lambda c: c.name == key, self.model.columns))
return AliasedColumn(self.alias, col)
except StopIteration:
raise KeyError(f"{key} is not a valid column name of {self.model.name}.")
def select(self, includes: list[str] = [], excludes: list[str] = []) -> 'Selection[M]':
"""
Creates a selection object containing selected columns in the model.
Args:
includes: Column names to select. All columns except specified in `excludes` are selected if empty.
excludes: Column names not to select.
Returns:
Selection object.
"""
columns = [c for c in self.model.columns if c.name not in excludes] \
if not bool(includes) else \
[c for c in self.model.columns if c.name not in excludes and c.name in includes]
return cast(Selection[M], Selection(self.model, self.alias, columns))
class Consumable:
@staticmethod
def to_consumable(value: Any) -> 'Consumable':
if isinstance(value, Consumable):
return value
elif isinstance(value, str):
return StrConsumable(value)
else:
return EmptyConsumable()
def __len__(self) -> int: ...
@property
def name(self) -> Optional[str]: ...
def consume(self, values: list[Any]) -> Any: ...
class StrConsumable(Consumable):
def __init__(self, key: str) -> None:
self.key = key
def __eq__(self, other: object) -> bool:
return isinstance(other, StrConsumable) and self.key == other.key
def __len__(self) -> int:
return 1
@property
def name(self) -> Optional[str]:
return self.key
def consume(self, values: list[Any]) -> Any:
return values[0]
class EmptyConsumable(Consumable):
def __eq__(self, other: object) -> bool:
return isinstance(other, EmptyConsumable)
def __len__(self) -> int:
return 1
@property
def name(self) -> Optional[str]:
return None
def consume(self, values: list[Any]) -> Any:
return values[0]
class Selection(Consumable, Generic[S]):
"""
A representation of table and its columns used in query.
This class is designed to be a bridge from query generation to reading results.
String expression of the instance is comma-separated column names prepended with alias, which can be embedded in the select query.
Due to `SelectMixin`, factory method is available on every model type.
```python
>>> s1 = table1.select("t1", includes = ["col11", "col12"])
>>> s2 = table2.select("t2")
>>> str(s1)
't1.col11, t1.col12'
>>> str(s2)
't2.col21, t2.col22, t2.col23'
```
The instances of this class are also used in `read_row` to reconstruct model objects from each obtained row.
```python
>>> c.execute(f"SELECT {s1}, {s2} FROM table1 AS t1 INNER JOIN table2 AS t2 ON ...")
>>> for row in c.fetchall():
>>> r = read_row(row, s1, s2)
>>> assert isinstance(r.t1, table1)
>>> assert isinstance(r.t2, table2)
```
"""
def __init__(self, table: type[S], alias: str, columns: list[Column]):
#: Model type.
self.table = table
#: An alias.
self.alias = alias
#: Columns to select.
self.columns = columns
@property
def name(self) -> str:
"""
Returns alias or name of the table.
"""
return self.alias if self.alias else cast(type[Model], self.table).name
def __len__(self) -> int:
return len(self.columns)
def __repr__(self) -> str:
a = f"{self.alias}." if self.alias else ""
return ', '.join([f"{a}{c.name}" for c in self.columns])
def __add__(self, other) -> 'FieldExpressions':
return FieldExpressions() + self + other
def __iter__(self):
return iter([self])
def __getattr__(self, key) -> AliasedColumn:
try:
return AliasedColumn(self.alias, next(filter(lambda c: c.name == key, self.columns)))
except StopIteration:
raise KeyError(f"{key} is not found from selected columns.")
def consume(self, values: list[Any]) -> S:
"""
Construct a model object from a row.
Args:
values: Values of row. The length must be equal to the number of columns in this.
Returns:
Model object where column values obtained from the row are set.
"""
return self.table(**dict([(c.name, v) for c, v in zip(self.columns, values)]))
class FieldExpressions:
"""
The instance of this class works as the composition of selections.
`+` operation on `Selection` s creates an instance of `FieldExpressions`. Each selection can be accessed via attributes of its name.
Also, `FieldExpression` can be extended by `+=`.
```python
>>> exp = table1.select("t1", includes=["col11", "col12"]) + table2.select("t2")
>>> c.execute(f"SELECT {exp} FROM table1 AS t1 INNER JOIN table2 AS t2 ON ...")
>>> for row in c.fetchall():
>>> r = read_row(row, *exp)
>>> assert isinstance(r.t1, table1)
>>> assert isinstance(r.t2, table2)
```
Here, empty tuple and string are also available instead of `Selection` instance.
They are replaced with index arguments (tuple) or keywords arguments (string) respectively by the invocation of the instance.
```python
>>> exp = table1.select("t1", includes=["col11", "col12"]) + () + "a" + () + "b"
>>> f"{exp("t2.col21", "t2.col23", a="t2.col22", b="t2.col24")}"
t1.col11, t1.col12, t2.col21, t2.col22, t2.col23, t2.col24
```
"""
def __init__(self):
self.__selections: list[Consumable] = []
self.__keys = {}
def __add__(self, other) -> Self:
exp = FieldExpressions()
exp += self
exp += other
return exp
def __iadd__(self, other) -> Self:
if isinstance(other, Selection):
self.__selections.append(other)
self.__keys[other.name] = other
elif isinstance(other, FieldExpressions):
self.__selections += other.__selections
self.__keys.update(other.__keys)
elif isinstance(other, str):
cons = StrConsumable(other)
self.__selections.append(cons)
self.__keys[other] = cons
elif other == ():
self.__selections.append(EmptyConsumable())
else:
raise ValueError(f"Operand of + for FieldExpressions must be a Selection or FieldExpressions but {type(other)} is given.")
return self
def __getitem__(self, index: int) -> Consumable:
return self.__selections[index]
def __getattr__(self, key: str) -> Consumable:
return self.__keys[key]
def __iter__(self) -> Iterator[Consumable]:
return iter(self.__selections)
class Instance:
def __init__(self, exp: 'FieldExpressions', *args, **kwargs):
self.exp = exp
self.args = args
self.kwargs = kwargs
def __repr__(self):
args = list(self.args)
def _repr(s: Consumable) -> str:
if isinstance(s, Selection):
return s.__repr__()
elif isinstance(s, StrConsumable):
return self.kwargs.get(s.key, s.key)
elif isinstance(s, EmptyConsumable):
return args.pop(0)
else:
raise ValueError(f"Unexpected expression type: {s}")
return ', '.join(map(_repr, self.exp))
def __call__(self, *args, **kwargs):
return FieldExpressions.Instance(self, *args, **kwargs)
def __repr__(self):
return self().__repr__()
class RowValues:
"""
This class provides attribute access to each row in query result.
Each instance returned by `read_row` behaves as if it is a list of consumed values of containing `Selection` s.
Index access returns the value at the index and iteration yields values in order.
```python
>>> exp = table1.select("t1"), table2.select()
>>> r = read_row(row, *exp)
>>> r[0]
...
>>> [v for v in r]
...
```
It also exposes attributes returns a `Selection` by its alias or table name.
```python
>>> r.t1
...
>>> r.table2
...
```
Args:
selections: List of selections which assign each value in row to a column.
"""
def __init__(self, selections: list[Consumable]):
self._key_map = dict([(s.name, i) for i, s in enumerate(selections) if s.name is not None])
self._values = []
def __len__(self):
return len(self._values)
def __iter__(self):
return iter(self._values)
def __getitem__(self, index):
return self._values[index]
def __getattr__(self, key) -> Any:
index = self._key_map.get(key, None)
if index is None:
raise AttributeError(f"No selection is found whose table name or alias is '{key}'")
return self._values[index]
def append(self, value: Any):
"""
Appends a value in the row.
Args:
value: A value in the row.
"""
self._values.append(value)
def read_row(row, *selections: Union[Consumable, str, tuple], allow_redundancy: bool = False) -> RowValues:
"""
Read values in a row according to given selections.
This function returns `RowValues` where each value is created by each selection respectively.
The type of the selection determines how values in the row are handled:
- `Selection` consumes as many values as the number of columns in it and creates a model instance.
- Empty tuple or a string consumes a value, which is stored in `RowValues` as it is.
Args:
selections: List of selections or their equivalents.
allow_redundancy: If `False`, `ValueError` is thrown when not all values in a row are consumed.
Returns:
Values read from the row accoding to the selections.
"""
consumables = [Consumable.to_consumable(s) for s in selections]
result = RowValues(consumables)
for s in consumables:
result.append(s.consume(row))
row = row[len(s):]
if not allow_redundancy and len(row) > 0:
raise ValueError("Not all elements in row is consumed.")
return result
class SelectMixin:
@overload
@classmethod
def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: Literal[False] = False) -> FieldExpressions: ...
@overload
@classmethod
def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: Literal[True] = True) -> Selection[Self]: ...
@classmethod
def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: bool = False):
"""
Default mixin class of every model type providing method to generate `Selection` by Selecting columns with alias.
Args:
alias: An alias string of this table.
includes: Column names to select. All columns except specified in `excludes` are selected if empty.
excludes: Column names not to select.
Returns:
Selection object.
"""
if single:
return Aliased(alias, cast(type, cls)).select(includes, excludes)
else:
return FieldExpressions() + Aliased(alias, cast(type, cls)).select(includes, excludes)
Functions
def read_row(row, *selections: Union[Consumable, str, tuple], allow_redundancy: bool = False) ‑> RowValues
-
Read values in a row according to given selections.
This function returns
RowValues
where each value is created by each selection respectively. The type of the selection determines how values in the row are handled:Selection
consumes as many values as the number of columns in it and creates a model instance.- Empty tuple or a string consumes a value, which is stored in
RowValues
as it is.
Args
selections
- List of selections or their equivalents.
allow_redundancy
- If
False
,ValueError
is thrown when not all values in a row are consumed.
Returns
Values read from the row accoding to the selections.
Expand source code
def read_row(row, *selections: Union[Consumable, str, tuple], allow_redundancy: bool = False) -> RowValues: """ Read values in a row according to given selections. This function returns `RowValues` where each value is created by each selection respectively. The type of the selection determines how values in the row are handled: - `Selection` consumes as many values as the number of columns in it and creates a model instance. - Empty tuple or a string consumes a value, which is stored in `RowValues` as it is. Args: selections: List of selections or their equivalents. allow_redundancy: If `False`, `ValueError` is thrown when not all values in a row are consumed. Returns: Values read from the row accoding to the selections. """ consumables = [Consumable.to_consumable(s) for s in selections] result = RowValues(consumables) for s in consumables: result.append(s.consume(row)) row = row[len(s):] if not allow_redundancy and len(row) > 0: raise ValueError("Not all elements in row is consumed.") return result
Classes
class Aliased (alias: str, model: type[~M])
-
A wrapper of a model type with an alias for it.
Expand source code
class Aliased(Generic[M]): """ A wrapper of a model type with an alias for it. """ def __init__(self, alias: str, model: type[M]) -> None: #: Alias string. self.alias = alias #: Model type. self.model = model def __getattr__(self, key: str) -> AliasedColumn: try: col = next(filter(lambda c: c.name == key, self.model.columns)) return AliasedColumn(self.alias, col) except StopIteration: raise KeyError(f"{key} is not a valid column name of {self.model.name}.") def select(self, includes: list[str] = [], excludes: list[str] = []) -> 'Selection[M]': """ Creates a selection object containing selected columns in the model. Args: includes: Column names to select. All columns except specified in `excludes` are selected if empty. excludes: Column names not to select. Returns: Selection object. """ columns = [c for c in self.model.columns if c.name not in excludes] \ if not bool(includes) else \ [c for c in self.model.columns if c.name not in excludes and c.name in includes] return cast(Selection[M], Selection(self.model, self.alias, columns))
Ancestors
- typing.Generic
Instance variables
var alias
-
Alias string.
var model
-
Model type.
Methods
def select(self, includes: list[str] = [], excludes: list[str] = []) ‑> Selection[~M]
-
Creates a selection object containing selected columns in the model.
Args
includes
- Column names to select. All columns except specified in
excludes
are selected if empty. excludes
- Column names not to select.
Returns
Selection object.
Expand source code
def select(self, includes: list[str] = [], excludes: list[str] = []) -> 'Selection[M]': """ Creates a selection object containing selected columns in the model. Args: includes: Column names to select. All columns except specified in `excludes` are selected if empty. excludes: Column names not to select. Returns: Selection object. """ columns = [c for c in self.model.columns if c.name not in excludes] \ if not bool(includes) else \ [c for c in self.model.columns if c.name not in excludes and c.name in includes] return cast(Selection[M], Selection(self.model, self.alias, columns))
class AliasedColumn (alias: str, column: Union[Column, str])
-
The representation of column and the alias of its belonging table.
The instance of this class works as
Q
's attribute as well. i.e. Condition on the column can be generated similarly to 'Q' via methods likeeq
.>>> c = AliasedColumn("t", "col") >>> c.eq(3) Condition: 't.col = $_' -- [3]
Expand source code
class AliasedColumn(Queryable[Any]): # type: ignore """ The representation of column and the alias of its belonging table. The instance of this class works as `Q` 's attribute as well. i.e. Condition on the column can be generated similarly to 'Q' via methods like `eq` . ```python >>> c = AliasedColumn("t", "col") >>> c.eq(3) Condition: 't.col = $_' -- [3] ``` """ def __init__(self, alias: str, column: Union[Column, str]) -> None: #: Alias string. self.alias = alias #: Column name or schema. self.column = column def __hash__(self) -> int: return hash(self.alias) + hash(self.column) def __eq__(self, other: object) -> bool: return isinstance(other, AliasedColumn) and self.alias == other.alias and self.column is other.column def __str__(self) -> str: return self.name @property def name(self) -> str: """ Aliased column name. If alias is empty, column name is returns as it is. """ if isinstance(self.column, Column): return f"{self.alias}.{self.column.name}" if self.alias else self.column.name else: return f"{self.alias}.{self.column}" if self.alias else self.column def __getattr__(self, key): method = getattr(Q, key) def invoke(value, *args, **kwargs): kwargs.update({self.name: value}) return method(*args, **kwargs) return invoke
Ancestors
- Queryable
- typing.Protocol
- typing.Generic
Instance variables
var alias
-
Alias string.
var column
-
Column name or schema.
var name : str
-
Aliased column name. If alias is empty, column name is returns as it is.
Expand source code
@property def name(self) -> str: """ Aliased column name. If alias is empty, column name is returns as it is. """ if isinstance(self.column, Column): return f"{self.alias}.{self.column.name}" if self.alias else self.column.name else: return f"{self.alias}.{self.column}" if self.alias else self.column
class Consumable
-
Expand source code
class Consumable: @staticmethod def to_consumable(value: Any) -> 'Consumable': if isinstance(value, Consumable): return value elif isinstance(value, str): return StrConsumable(value) else: return EmptyConsumable() def __len__(self) -> int: ... @property def name(self) -> Optional[str]: ... def consume(self, values: list[Any]) -> Any: ...
Subclasses
Static methods
def to_consumable(value: Any) ‑> Consumable
-
Expand source code
@staticmethod def to_consumable(value: Any) -> 'Consumable': if isinstance(value, Consumable): return value elif isinstance(value, str): return StrConsumable(value) else: return EmptyConsumable()
Instance variables
var name : Optional[str]
-
Expand source code
@property def name(self) -> Optional[str]: ...
Methods
def consume(self, values: list[typing.Any]) ‑> Any
-
Expand source code
def consume(self, values: list[Any]) -> Any: ...
class EmptyConsumable
-
Expand source code
class EmptyConsumable(Consumable): def __eq__(self, other: object) -> bool: return isinstance(other, EmptyConsumable) def __len__(self) -> int: return 1 @property def name(self) -> Optional[str]: return None def consume(self, values: list[Any]) -> Any: return values[0]
Ancestors
Instance variables
var name : Optional[str]
-
Expand source code
@property def name(self) -> Optional[str]: return None
Methods
def consume(self, values: list[typing.Any]) ‑> Any
-
Expand source code
def consume(self, values: list[Any]) -> Any: return values[0]
class FieldExpressions
-
The instance of this class works as the composition of selections.
+
operation onSelection
s creates an instance ofFieldExpressions
. Each selection can be accessed via attributes of its name. Also,FieldExpression
can be extended by+=
.>>> exp = table1.select("t1", includes=["col11", "col12"]) + table2.select("t2") >>> c.execute(f"SELECT {exp} FROM table1 AS t1 INNER JOIN table2 AS t2 ON ...") >>> for row in c.fetchall(): >>> r = read_row(row, *exp) >>> assert isinstance(r.t1, table1) >>> assert isinstance(r.t2, table2)
Here, empty tuple and string are also available instead of
Selection
instance. They are replaced with index arguments (tuple) or keywords arguments (string) respectively by the invocation of the instance.>>> exp = table1.select("t1", includes=["col11", "col12"]) + () + "a" + () + "b" >>> f"{exp("t2.col21", "t2.col23", a="t2.col22", b="t2.col24")}" t1.col11, t1.col12, t2.col21, t2.col22, t2.col23, t2.col24
Expand source code
class FieldExpressions: """ The instance of this class works as the composition of selections. `+` operation on `Selection` s creates an instance of `FieldExpressions`. Each selection can be accessed via attributes of its name. Also, `FieldExpression` can be extended by `+=`. ```python >>> exp = table1.select("t1", includes=["col11", "col12"]) + table2.select("t2") >>> c.execute(f"SELECT {exp} FROM table1 AS t1 INNER JOIN table2 AS t2 ON ...") >>> for row in c.fetchall(): >>> r = read_row(row, *exp) >>> assert isinstance(r.t1, table1) >>> assert isinstance(r.t2, table2) ``` Here, empty tuple and string are also available instead of `Selection` instance. They are replaced with index arguments (tuple) or keywords arguments (string) respectively by the invocation of the instance. ```python >>> exp = table1.select("t1", includes=["col11", "col12"]) + () + "a" + () + "b" >>> f"{exp("t2.col21", "t2.col23", a="t2.col22", b="t2.col24")}" t1.col11, t1.col12, t2.col21, t2.col22, t2.col23, t2.col24 ``` """ def __init__(self): self.__selections: list[Consumable] = [] self.__keys = {} def __add__(self, other) -> Self: exp = FieldExpressions() exp += self exp += other return exp def __iadd__(self, other) -> Self: if isinstance(other, Selection): self.__selections.append(other) self.__keys[other.name] = other elif isinstance(other, FieldExpressions): self.__selections += other.__selections self.__keys.update(other.__keys) elif isinstance(other, str): cons = StrConsumable(other) self.__selections.append(cons) self.__keys[other] = cons elif other == (): self.__selections.append(EmptyConsumable()) else: raise ValueError(f"Operand of + for FieldExpressions must be a Selection or FieldExpressions but {type(other)} is given.") return self def __getitem__(self, index: int) -> Consumable: return self.__selections[index] def __getattr__(self, key: str) -> Consumable: return self.__keys[key] def __iter__(self) -> Iterator[Consumable]: return iter(self.__selections) class Instance: def __init__(self, exp: 'FieldExpressions', *args, **kwargs): self.exp = exp self.args = args self.kwargs = kwargs def __repr__(self): args = list(self.args) def _repr(s: Consumable) -> str: if isinstance(s, Selection): return s.__repr__() elif isinstance(s, StrConsumable): return self.kwargs.get(s.key, s.key) elif isinstance(s, EmptyConsumable): return args.pop(0) else: raise ValueError(f"Unexpected expression type: {s}") return ', '.join(map(_repr, self.exp)) def __call__(self, *args, **kwargs): return FieldExpressions.Instance(self, *args, **kwargs) def __repr__(self): return self().__repr__()
Class variables
var Instance
class RowValues (selections: list[Consumable])
-
This class provides attribute access to each row in query result.
Each instance returned by
read_row()
behaves as if it is a list of consumed values of containingSelection
s. Index access returns the value at the index and iteration yields values in order.>>> exp = table1.select("t1"), table2.select() >>> r = read_row(row, *exp) >>> r[0] ... >>> [v for v in r] ...
It also exposes attributes returns a
Selection
by its alias or table name.>>> r.t1 ... >>> r.table2 ...
Args
selections
- List of selections which assign each value in row to a column.
Expand source code
class RowValues: """ This class provides attribute access to each row in query result. Each instance returned by `read_row` behaves as if it is a list of consumed values of containing `Selection` s. Index access returns the value at the index and iteration yields values in order. ```python >>> exp = table1.select("t1"), table2.select() >>> r = read_row(row, *exp) >>> r[0] ... >>> [v for v in r] ... ``` It also exposes attributes returns a `Selection` by its alias or table name. ```python >>> r.t1 ... >>> r.table2 ... ``` Args: selections: List of selections which assign each value in row to a column. """ def __init__(self, selections: list[Consumable]): self._key_map = dict([(s.name, i) for i, s in enumerate(selections) if s.name is not None]) self._values = [] def __len__(self): return len(self._values) def __iter__(self): return iter(self._values) def __getitem__(self, index): return self._values[index] def __getattr__(self, key) -> Any: index = self._key_map.get(key, None) if index is None: raise AttributeError(f"No selection is found whose table name or alias is '{key}'") return self._values[index] def append(self, value: Any): """ Appends a value in the row. Args: value: A value in the row. """ self._values.append(value)
Methods
def append(self, value: Any)
-
Appends a value in the row.
Args
value
- A value in the row.
Expand source code
def append(self, value: Any): """ Appends a value in the row. Args: value: A value in the row. """ self._values.append(value)
class SelectMixin
-
Expand source code
class SelectMixin: @overload @classmethod def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: Literal[False] = False) -> FieldExpressions: ... @overload @classmethod def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: Literal[True] = True) -> Selection[Self]: ... @classmethod def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: bool = False): """ Default mixin class of every model type providing method to generate `Selection` by Selecting columns with alias. Args: alias: An alias string of this table. includes: Column names to select. All columns except specified in `excludes` are selected if empty. excludes: Column names not to select. Returns: Selection object. """ if single: return Aliased(alias, cast(type, cls)).select(includes, excludes) else: return FieldExpressions() + Aliased(alias, cast(type, cls)).select(includes, excludes)
Subclasses
Static methods
def select(alias: str = '', includes: list[str] = [], excludes: list[str] = [], single: bool = False)
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Default mixin class of every model type providing method to generate
Selection
by Selecting columns with alias.Args
alias
- An alias string of this table.
includes
- Column names to select. All columns except specified in
excludes
are selected if empty. excludes
- Column names not to select.
Returns
Selection object.
Expand source code
@classmethod def select(cls, alias: str = "", includes: list[str] = [], excludes: list[str] = [], single: bool = False): """ Default mixin class of every model type providing method to generate `Selection` by Selecting columns with alias. Args: alias: An alias string of this table. includes: Column names to select. All columns except specified in `excludes` are selected if empty. excludes: Column names not to select. Returns: Selection object. """ if single: return Aliased(alias, cast(type, cls)).select(includes, excludes) else: return FieldExpressions() + Aliased(alias, cast(type, cls)).select(includes, excludes)
class Selection (table: type[~S], alias: str, columns: list[Column])
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A representation of table and its columns used in query.
This class is designed to be a bridge from query generation to reading results. String expression of the instance is comma-separated column names prepended with alias, which can be embedded in the select query.
Due to
SelectMixin
, factory method is available on every model type.>>> s1 = table1.select("t1", includes = ["col11", "col12"]) >>> s2 = table2.select("t2") >>> str(s1) 't1.col11, t1.col12' >>> str(s2) 't2.col21, t2.col22, t2.col23'
The instances of this class are also used in
read_row()
to reconstruct model objects from each obtained row.>>> c.execute(f"SELECT {s1}, {s2} FROM table1 AS t1 INNER JOIN table2 AS t2 ON ...") >>> for row in c.fetchall(): >>> r = read_row(row, s1, s2) >>> assert isinstance(r.t1, table1) >>> assert isinstance(r.t2, table2)
Expand source code
class Selection(Consumable, Generic[S]): """ A representation of table and its columns used in query. This class is designed to be a bridge from query generation to reading results. String expression of the instance is comma-separated column names prepended with alias, which can be embedded in the select query. Due to `SelectMixin`, factory method is available on every model type. ```python >>> s1 = table1.select("t1", includes = ["col11", "col12"]) >>> s2 = table2.select("t2") >>> str(s1) 't1.col11, t1.col12' >>> str(s2) 't2.col21, t2.col22, t2.col23' ``` The instances of this class are also used in `read_row` to reconstruct model objects from each obtained row. ```python >>> c.execute(f"SELECT {s1}, {s2} FROM table1 AS t1 INNER JOIN table2 AS t2 ON ...") >>> for row in c.fetchall(): >>> r = read_row(row, s1, s2) >>> assert isinstance(r.t1, table1) >>> assert isinstance(r.t2, table2) ``` """ def __init__(self, table: type[S], alias: str, columns: list[Column]): #: Model type. self.table = table #: An alias. self.alias = alias #: Columns to select. self.columns = columns @property def name(self) -> str: """ Returns alias or name of the table. """ return self.alias if self.alias else cast(type[Model], self.table).name def __len__(self) -> int: return len(self.columns) def __repr__(self) -> str: a = f"{self.alias}." if self.alias else "" return ', '.join([f"{a}{c.name}" for c in self.columns]) def __add__(self, other) -> 'FieldExpressions': return FieldExpressions() + self + other def __iter__(self): return iter([self]) def __getattr__(self, key) -> AliasedColumn: try: return AliasedColumn(self.alias, next(filter(lambda c: c.name == key, self.columns))) except StopIteration: raise KeyError(f"{key} is not found from selected columns.") def consume(self, values: list[Any]) -> S: """ Construct a model object from a row. Args: values: Values of row. The length must be equal to the number of columns in this. Returns: Model object where column values obtained from the row are set. """ return self.table(**dict([(c.name, v) for c, v in zip(self.columns, values)]))
Ancestors
- Consumable
- typing.Generic
Instance variables
var alias
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An alias.
var columns
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Columns to select.
var name : str
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Returns alias or name of the table.
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@property def name(self) -> str: """ Returns alias or name of the table. """ return self.alias if self.alias else cast(type[Model], self.table).name
var table
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Model type.
Methods
def consume(self, values: list[typing.Any]) ‑> ~S
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Construct a model object from a row.
Args
values
- Values of row. The length must be equal to the number of columns in this.
Returns
Model object where column values obtained from the row are set.
Expand source code
def consume(self, values: list[Any]) -> S: """ Construct a model object from a row. Args: values: Values of row. The length must be equal to the number of columns in this. Returns: Model object where column values obtained from the row are set. """ return self.table(**dict([(c.name, v) for c, v in zip(self.columns, values)]))
class StrConsumable (key: str)
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class StrConsumable(Consumable): def __init__(self, key: str) -> None: self.key = key def __eq__(self, other: object) -> bool: return isinstance(other, StrConsumable) and self.key == other.key def __len__(self) -> int: return 1 @property def name(self) -> Optional[str]: return self.key def consume(self, values: list[Any]) -> Any: return values[0]
Ancestors
Instance variables
var name : Optional[str]
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@property def name(self) -> Optional[str]: return self.key
Methods
def consume(self, values: list[typing.Any]) ‑> Any
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def consume(self, values: list[Any]) -> Any: return values[0]