如何使用SQLAlchemy TypeDecorators编译原始SQL

Question

我有一个SqlAlchemy查询对象，它使用uuid.UUID

import uuid
import sqlalchemy

foreign_uuid = '822965bb-c67e-47ee-ad12-a3b060ef79ae'
qry = Query(MyModel).filter(MyOtherModel.uuid == uuid.UUID(foreign_uuid))

现在，我想从SQLAlchemy获得原始postgresql：

qry.statement.compile(dialect=postgresql.dialect(), compile_kwargs={"literal_binds": True}))

这会产生以下错误：NotImplementedError: Don't know how to literal-quote value UUID('822965bb-c67e-47ee-ad12-a3b060ef79ae')

这似乎是因为SqlAlchemy只知道如何处理基本类型。文件显示使用TypeDecorator，甚至为GUID提供一个：

from sqlalchemy.dialects.postgresql import UUID
import uuid

class GUID(TypeDecorator):
    """Platform-independent GUID type.

    Uses PostgreSQL's UUID type, otherwise uses
    CHAR(32), storing as stringified hex values.

    """
    impl = CHAR

    def load_dialect_impl(self, dialect):
        if dialect.name == 'postgresql':
            return dialect.type_descriptor(UUID())
        else:
            return dialect.type_descriptor(CHAR(32))

    def process_bind_param(self, value, dialect):
        if value is None:
            return value
        elif dialect.name == 'postgresql':
            return str(value)
        else:
            if not isinstance(value, uuid.UUID):
                return "%.32x" % uuid.UUID(value).int
            else:
                # hexstring
                return "%.32x" % value.int

    def process_result_value(self, value, dialect):
        if value is None:
            return value
        else:
            if not isinstance(value, uuid.UUID):
                value = uuid.UUID(value)
            return value

然而，它并没有说明如何使用这个TypeDecorator。我需要在我的模型中引用它吗？我是否以某种方式使它可用于.statement.compile呼叫？

Answer 1

使用修饰类型作为列类型。另一组文档更清楚地解释了它：https://docs.sqlalchemy.org/en/14/faq/sqlexpressions.html#faq-sql-expression-string

   from sqlalchemy import TypeDecorator, Integer

 
   class MyFancyType(TypeDecorator):
       impl = Integer

       def process_literal_param(self, value, dialect):
           return "my_fancy_formatting(%s)" % value

   from sqlalchemy import Table, Column, MetaData

      tab = Table('mytable', MetaData(), Column('x', MyFancyType()))