Question

I am trying to convert old sqlite3 code to sql alchemy. I am trying to make sense of how best to handle my use case. I am new to the ORM method of database access.

I am trying to dynamically generate unique table names based on a common definition. I have read the mixins guide as well as the post on how to use var url = hyperL.getFormulaR1C1(); to dynamically declare classes, but I am still unsure how of I would go about this. Here is what I have so far:

type

If I try to use this, it doesn't work:

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey
from sqlalchemy.ext.declarative import declared_attr

Base = declarative_base()


class DynamicName(object):
    @declared_attr
    def __tablename__(cls):
        return cls.__name__.lower()

class Genome(DynamicName, Base):
    __tablename__ = 'AbstractGenome'
    AlignmentId = Column(Integer, primary_key=True)
    StartOutOfFrame = Column(Integer)
    BadFrame = Column(Integer)

def build_genome_table(genome):
    d = {'__tablename__': genome}
    table = type(genome, (Genome,), d)
    return table

How do I go about dynamically generating a >>> from sqlalchemy import create_engine >>> engine = create_engine('sqlite:///:memory:', echo=True) >>> genomes = ["A", "B"] >>> tables = {x: build_genome_table(x) for x in genomes} Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 1, in <dictcomp> File "<stdin>", line 3, in build_genome_table File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py", line 55, in __init__ _as_declarative(cls, classname, cls.__dict__) File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 88, in _as_declarative _MapperConfig.setup_mapping(cls, classname, dict_) File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 103, in setup_mapping cfg_cls(cls_, classname, dict_) File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 135, in __init__ self._early_mapping() File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 138, in _early_mapping self.map() File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 529, in map **self.mapper_args File "<string>", line 2, in mapper File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 623, in __init__ self._configure_inheritance() File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 930, in _configure_inheritance self.local_table) File "<string>", line 2, in join_condition File "/cluster/home/ifiddes/python2.7/lib/python2.7/site-packages/sqlalchemy/sql/selectable.py", line 839, in _join_condition (a.description, b.description, hint)) sqlalchemy.exc.NoForeignKeysError: Can't find any foreign key relationships between 'AbstractGenome' and 'A'. table based on a passed name? I also would ideally like a setup where I can have hierarchical inheritance, so that I can declare different subclasses like Genome or ReferenceGenome which have additional columns but also can have dynamic names.

Answer 1

请参阅：sqlalchemy.orm.mapper：http://docs.sqlalchemy.org/en/latest/orm/mapping_api.html#class-mapping-api。我的理解（因为我过去只使用此函数修改过代码）是它直接将模型类映射到Table对象，该对象本身连接到数据库表。

这个用例听起来非常类似于食谱history_meta：http://docs.sqlalchemy.org/en/latest/_modules/examples/versioned_history/history_meta.html。排序可能需要一些时间，但是这里基于现有模型（Versioned的任何子类）动态创建Table对象，然后在创建类时直接映射到数据库表。

这是问题所在：您确实需要一个实际的数据库表来映射。毕竟这是一个ORM。你有几个选择：

如果要动态创建将在数据库中保留的表，可以按照此处使用Table.create（）：http://docs.sqlalchemy.org/en/latest/core/metadata.html#creating-and-dropping-database-tables
如果您只需要偶尔创建表格，则可以与alembic集成：https://pypi.python.org/pypi/alembic
如果您只需要一个进程，而且再也不需要它，您可以创建临时表，但我不确定SQLAlchemy是否直接支持它。我检查的少数资源似乎正在使用create（）和drop（）。我没有使用过SQLAlchemy 1.0+，所以它可能会在某些我没见过的地方得到支持。

如果有什么不清楚，请告诉我。我玩了history_meta.py已经有一段时间了，所以我可能会生锈。

dynamic table names with SQLalchemy

1 个答案: