Question

我有一个关于使用SQLAlchemy制作PostgreSQL表继承的问题。

我有两张桌子：

CREATE TABLE his
(
  idg integer,
  idfk integer,
  idh integer NOT NULL defautl nextval('his_seq'),
  "type" character varying,
  CONSTRAINT __his_pkey PRIMARY KEY (idh)
);
CREATE TABLE data
(
  "text" character varying,
)
INHERITS (his);

在执行任何ddl命令之前，我已经创建了这个python代码：

from sqlalchemy  import *
from sqlalchemy.orm import Session
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event

Base = declarative_base()

class His(Base):
    __tablename__ = 'his'

    idg = Column(Integer())
    idfk = Column(Integer())
    idh = Column(Integer(), Sequence('his_seq',  start=1,  increment=1),  primary_key=True)
    type= Column(String())

    __mapper_args__ = {'polymorphic_on': type}
    __table_args__ = {'implicit_returning':False}

    def __init__(self,  idg,  idfk,  type):
        self.idg = idg
        self.idfk = idfk
        self.type = type

class Data(His):
    __tablename__ = None
#    __mapper_args__ = {'polymorphic_identity': 'data',  'concrete':True}
    __mapper_args__ = {'polymorphic_identity': 'data'}
    text = Column(String())

    def __init__(self, text):
        self.text = text

@event.listens_for(His.__table__,  'after_create')
def create_child_tables(target, connection,  **kw):   
    connection.execute("""
        CREATE TABLE data(
        ) INHERITS (his)
    """)

    connection.execute("""
        CREATE OR REPLACE FUNCTION his_insert_trigger()
        RETURNS TRIGGER AS $$
        BEGIN
            IF (NEW.type='data') THEN
                INSERT INTO data VALUES (NEW.*);
            ELSE
                RAISE EXCEPTION 'Table type is unknown for historical porpurses.';
            END IF;
        RETURN NULL;
        END;
        $$
        LANGUAGE plpgsql;    
    """)

    connection.execute("""
        CREATE TRIGGER his_insert
        BEFORE INSERT ON his
        FOR EACH ROW EXECUTE PROCEDURE his_insert_trigger();
    """)

@event.listens_for(His.__table__, "before_drop")
def create_child_tables(target, connection, **kw):
    connection.execute("drop table data")
    connection.execute("drop table his")
    connection.execute("drop sequence his_seq")

e = create_engine('postgresql://localhost:5433/des', echo=True)
#Base.metadata.drop_all(e)
Base.metadata.create_all(e)
s = Session(e)

s.add_all([
    Data('hola'), 
    Data('pedorrete'), 
    Data('pedorrete2')
])

s.commit()
s.close()

嗯，这个例子（如http://www.sqlalchemy.org/trac/wiki/UsageRecipes/PostgreSQLInheritance中所解释的）创建了两个表，但是sqlalchemy总是使用他的表来插入数据记录，并将这些表插入到数据和他的数据中。文本字段（在数据上）确实是在他的桌子上创建的。

那么，有没有办法指定SQLAchemy数据表必须从他继承（Postgres继承），并且必须向其添加文本字段，并且当我在数据上插入任何记录时必须使用数据而不是他？ / p>

问候。

Answer 1

SQLAlchemy尝试尽可能地移植，因此它不支持许多Postgres特有的功能。这是从SA家伙给有类似问题的人给出的答案： http://www.mail-archive.com/sqlalchemy@googlegroups.com/msg17443.html

使用SQLAlchemy进行Postgres继承

1 个答案: