我正在使用SQLalchemy与automap和一系列SQLite数据库产生的程序，我无法控制。但是，我需要扩展数据库以提供额外的功能，所以我使用SQLalchemy ORM修改这个数据库，并使用automap访问我没有更改的表和列。在

类定义(保留在自己的模块中)：Base = automap_base()

class VariantAssociation(Base):

__tablename__ = "sample_variant_association"

vid = Column(Integer, ForeignKey("variants.variant_id"),

primary_key=True, index=True)

sid = Column(Integer, ForeignKey("samples.sample_id"),

primary_key=True, index=True)

vdepth = Column(Integer, index=True)

valt_depth = Column(Integer, index=True)

gt = Column(Text)

gt_type = Column(Integer)

fraction = Column(Float, index=True)

variant = relationship("Variant", back_populates="samples")

sample = relationship("Samples", back_populates="variants")

class Variant(Base):

__tablename__ = "variants"

variant_id = Column(Integer, primary_key=True)

info = deferred(Column(LargeBinary))

samples = relationship("VariantAssociation",

back_populates="variant")

compressed = False

_gt_alt_depths = None

_gt_depths = None

_gts = None

_gt_types = None

def decompress(self, compressed=False):

if compressed:

unpack = snappy_unpack_blob

else:

unpack = unpack_blob

self._gt_alt_depths = unpack(self.gt_alt_depths)

self._gt_depths = unpack(self.gt_depths)

self._gts = unpack(self.gts)

self._gt_types = unpack(self.gt_types)

def __repr__(self):

data = ""

return data.format(chrom=self.chrom,

start=self.start,

end=self.end,

gene=self.gene,

ref=self.ref,

alt=self.alt,

type=self.type)

@property

def alt_depths(self):

return self._gt_alt_depths

@property

def depths(self):

return self._gt_depths

@property

def genotypes(self):

return self._gts

@property

def genotype_types(self):

return self._gt_types

class Samples(Base):

__tablename__ = "samples"

sample_id = Column(Integer, primary_key=True, index=True)

name = Column(Text, index=True)

variants = relationship("VariantAssociation",

back_populates="sample")

class DataMigration(Base):

__tablename__ = "datamigration"

done = Column(Boolean, primary_key=True)

然后我用这种方法加载数据库(在另一个函数中，它从定义表的地方导入Base)：

^{pr2}$

但是，如果我加载两个数据库，无论第一次泄漏到后续运行中发生什么情况：db = load_database("file1.db") # All right

db2 = load_database("file2.db") # Throws exception

例外情况是：io.py in load_database(database)

150

151 # Create association table if not present

--> 152 VariantAssociation.__table__.create(bind=engine, checkfirst=True)

153 DataMigration.__table__.create(bind=engine, checkfirst=True)

154

[cut exception all into SQLalchemy internals]

OperationalError: (sqlite3.OperationalError) index ix_sample_variant_association_valt_depth already exists [SQL: 'CREATE INDEX ix_sample_variant_association_valt_depth ON sample_variant_association (valt_depth)']

如果我在单独的会话中加载数据库，则不会发生这种情况，因此db的状态正以某种方式泄漏到db2。在

确保每个加载的数据库ORM是独立的最好方法是什么？在

编辑：更多调试显示，CREATE INDEX被使用了两次：2017-09-15 15:18:00,284 INFO sqlalchemy.engine.base.Engine ()

2017-09-15 15:18:00,417 INFO sqlalchemy.engine.base.Engine COMMIT

2017-09-15 15:18:00,418 INFO sqlalchemy.engine.base.Engine CREATE INDEX

ix_sample_variant_association_valt_depth ON sample_variant_association

(valt_depth)

2017-09-15 15:18:00,418 INFO sqlalchemy.engine.base.Engine ()

2017-09-15 15:18:00,550 INFO sqlalchemy.engine.base.Engine COMMIT

2017-09-15 15:18:00,551 INFO sqlalchemy.engine.base.Engine CREATE INDEX

ix_sample_variant_association_valt_depth ON sample_variant_association

(valt_depth)