问题描述
我正在尝试使用最初为 Postgres 数据库设计的 sqlAlchemy ORM 创建内存中的 sqlite 数据库。为了让 sqlite 引擎能够转换 postgres 特定的数据类型,我依赖于 sqlAlchemy @compiles
装饰器,该装饰器适用于 sqlalchemy.dialects.postgresql
命名空间中的类型。
如何将 geoalchemy2.Raster
数据类型转换为与引擎无关的数据类型(对于我而言,它可能是 sqlalchemy.BLOB
类型。重要的是我可以创建类似的表,它们不需要精确)?
此示例代码按预期转换 DOUBLE_PRECISION
类型,但我不知道如何修改 geoalchemy2.Raster
数据类型,即 UserDefinedType
。我希望能够编写与 compile_DOUBLE_PRECISION()
类似的方法,将 Raster
更改为 BLOB
类型。
import sqlalchemy
from sqlalchemy import Column,Integer
from sqlalchemy.dialects.postgresql import DOUBLE_PRECISION
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.dialects.sqlite.base import sqliteTypeCompiler
from geoalchemy2 import Raster
Base = declarative_base()
class SomeModel(Base):
__tablename__ = "some_model"
id = Column(Integer,primary_key=True)
double_precision = Column(DOUBLE_PRECISION)
raster = Column(Raster)
# The following @compiles works as intended
@compiles(DOUBLE_PRECISION,'sqlite')
def compile_DOUBLE_PRECISION(element,compiler: sqliteTypeCompiler,**kw):
""" Handles postgres DOUBLE_PRECISION datatype as REAL in sqlite. """
return compiler.visit_real(element,**kw)
def test_throws_error_due_to_raster_data_type():
engine = sqlalchemy.create_engine("sqlite:///:memory:")
Base.Metadata.create_all(engine)
解决方法
我不熟悉 postgresql 但也许这样的东西可以工作
import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
from geoalchemy2 import Raster
Base = declarative_base()
def raster_if_postgresql_else_blob():
return sa.BLOB().with_variant(Raster,"postgresql")
class SomeModel(Base):
__tablename__ = "some_model"
id = sa.Column(sa.Integer,primary_key=True)
raster = sa.Column(raster_if_postgresql_else_blob())
lite_engine = sa.create_engine("sqlite:///:memory:",echo=True)
Base.metadata.create_all(lite_engine)