the canonical solution is the"entity name" pattern at
https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes/EntityName,
however this does establish subclasses-per-table even though it is
automated.
To truly use just a single class, the caveat is that the identity map
will not have any cue to store the object from a different table if it
already has an identity of that row (there is an "identity_token"
feature that can also work around this, it's new and experimental but
i can illustrate if you want to get into that).
For single class see the example below.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
Base = declarative_base()
class A(Base):
__tablename__ = 'a'
id = Column(Integer, primary_key=True)
x = Column(Integer)
y = Column(Integer)
def __repr__(self):
return "A(id=%r, x=%r, y=%r)" % (self.id, self.x, self.y)
e = create_engine("sqlite://", echo=True)
with e.connect() as conn:
conn.execute("""
CREATE TABLE a (
id INTEGER NOT NULL, x INTEGER, y INTEGER, PRIMARY KEY (id)
)
""")
conn.execute("""
CREATE TABLE b (
id INTEGER NOT NULL, x INTEGER, y INTEGER, PRIMARY KEY (id)
)
""")
conn.execute("""
CREATE TABLE c (
id INTEGER NOT NULL, x INTEGER, y INTEGER, PRIMARY KEY (id)
)
""")
conn.execute("INSERT INTO a (id, x, y) VALUES (1, 2, 3), (4, 5, 6)")
conn.execute("INSERT INTO b (id, x, y) VALUES (7, 8, 9), (10, 11, 12)")
conn.execute("INSERT INTO c (id, x, y) VALUES (13, 14, 15), (16, 17, 18)")
s = Session(e)
b_table = Table('b', Base.metadata, autoload_with=e)
c_table = Table('c', Base.metadata, autoload_with=e)
print(s.query(A).all())
# if overlapping primary keys between "a" and "b", need to remove all "A"
# instances to load them from "b", these are in the identity map against table
# "a". Use the full "entity name" pattern, or the identity_token, to avoid this
s.close()
print(s.query(A).select_entity_from(
aliased(A, b_table, adapt_on_names=True)).all())
# if overlapping primary keys between "b" and "c", need to remove all "A"
# instances to load them from "c", these are in the identity map against table
# "b". Use the full "entity name" pattern, or the identity_token, to avoid this
s.close()
print(s.query(A).select_entity_from(
aliased(A, c_table, adapt_on_names=True)).all())
On Sat, Mar 3, 2018 at 2:45 AM, Stanislav Lobanov <[email protected]> wrote:
> Hello!
>
> I have a database with 10 tables with same structure. This structure of a
> tables are always the same.
>
> I want to be able to query this tables using one declarative mapper instead
> of 10 similar mappers, but to do so i need a way to change table name
> somehow.
>
> Desired code:
>
> class T(Base):
> some_column = Column(Integer) # just an example
>
> table_a_results =
> session.query(T).select_from_table('table_a').filter(T.some_column >
> 10).count()
> table_b_results =
> session.query(T).select_from_table('table_b').filter(T.some_column >
> 10).count()
>
>
> Are there any possibility to implement such query feature? Are there any
> alternative variants to this feature?
>
> Thanks!
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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