SqlAlchemy:Postgresql自定义类型的数组

Question

所以在我的postgres DB中我有以下自定义类型:

create type my_pg_type as (  
    sting_id varchar(32),
    time_diff interval,
    multiplier integer
);

为了进一步复杂化,这被用作数组:

alter table my_table add column my_keys my_pg_type [];

我想用SQLAlchemy(0.6.4)来映射它!

(为长生不老道歉)

from sqlalchemy.dialects.postgresql import ARRAY
from sqlalchemy.types import Enum
from elixir import Entity, Field    

class MyTable(Entity):
    # -- snip --
    my_keys = Field(ARRAY(Enum))

我知道'Enum'在上面是不正确的.

有关从该数组的数据库返回的值的示例,我在下面显示了以下值ARRAY.result_processor(self, dialect, coltype):

class ARRAY(sqltypes.MutableType, sqltypes.Concatenable, sqltypes.TypeEngine):
    # -- snip --  
    def result_processor(self, dialect, coltype):
        item_proc = self.item_type.result_processor(dialect, coltype)
        if item_proc:
            def convert_item(item):
                if isinstance(item, list):
                    return [convert_item(child) for child in item]
                else:
                    return item_proc(item)
        else:
            def convert_item(item):
                if isinstance(item, list):
                    return [convert_item(child) for child in item]
                else:
                    return item
        def process(value):
            if value is None:
                return value
            """
            # sample value:
             >>> value
            '{"(key_1,07:23:00,0)","(key_2,01:00:00,20)"}'
            """
            return [convert_item(item) for item in value]
        return process

所以上面的process函数错误地拆分了字符串,假设它已经是一个列表.

到目前为止,我已经成功地将ARRAY子类化为正确分割字符串,而不是Enum,我尝试编写自己的类型(实现Unicode)来重新创建(string, timedelta, integer)元组,但遇到了很多困难,特别是正确的转换为intervalPython timedelta.

我在这里张贴,以防我错过了一个明显的先例方法吗？

Answer 1

更新请参阅底部的配方以获取解决方法

我编写了一些示例代码来查看psycopg2在这里做了什么,这完全在他们的领域内 - psycopg2根本没有将值解释为数组.当它返回时,psycopg2需要能够解析ARRAY,因为SQLA的ARRAY类型至少假定已经完成了很多.你当然可以破解SQLAlchemy的ARRAY,这里的意思是基本上不会使用它来支持解析psycopg2给我们回来的特定字符串值的东西.

但是这里也发生的事情是我们甚至没有获得psycopg2的转换timedeltas的机制,SQLAlchemy通常不必担心.在这种情况下,我觉得DBAPI的设施未得到充分利用,psycopg2是一个非常强大的DBAPI.

因此,我建议您使用psycopg2的自定义类型机制来处理http://initd.org/psycopg/docs/extensions.html#database-types-casting-functions.

如果你想邮寄他们的邮件列表,这是一个测试案例:

import psycopg2

conn = psycopg2.connect(host="localhost", database="test", user="scott", password="tiger")
cursor = conn.cursor()
cursor.execute("""
create type my_pg_type as (  
    string_id varchar(32),
    time_diff interval,
    multiplier integer
)
""")

cursor.execute("""
    CREATE TABLE my_table (
        data my_pg_type[]
    )
""")

cursor.execute("insert into my_table (data) "
            "values (CAST(%(data)s AS my_pg_type[]))", 
            {'data':[("xyz", "'1 day 01:00:00'", 5), ("pqr", "'1 day 01:00:00'", 5)]})

cursor.execute("SELECT * from my_table")
row = cursor.fetchone()
assert isinstance(row[0], (tuple, list)), repr(row[0])

PG的类型注册支持全局注册.您还可以在SQLAlchemy中使用0.6中的池侦听器或0.7中的连接事件在每个连接上注册类型.

UPDATE -由于https://bitbucket.org/zzzeek/sqlalchemy/issue/3467/array-of-enums-does-not-allow-assigning我可能会建议人们使用此解决方案类型现在,直到psycopg2为此增加了更多内置支持:

class ArrayOfEnum(ARRAY):

    def bind_expression(self, bindvalue):
        return sa.cast(bindvalue, self)

    def result_processor(self, dialect, coltype):
        super_rp = super(ArrayOfEnum, self).result_processor(dialect, coltype)

        def handle_raw_string(value):
            inner = re.match(r"^{(.*)}$", value).group(1)
            return inner.split(",")

        def process(value):
            return super_rp(handle_raw_string(value))
        return process

Answer 2

查看sqlalchemy_utils文档：

CompositeType provides means to interact with
`PostgreSQL composite types`_. Currently this type features:

* Easy attribute access to composite type fields
* Supports SQLAlchemy TypeDecorator types
* Ability to include composite types as part of PostgreSQL arrays
* Type creation and dropping

用法：

from collections import OrderedDict

import sqlalchemy as sa
from sqlalchemy_utils import Composite, CurrencyType


class Account(Base):
    __tablename__ = 'account'
    id = sa.Column(sa.Integer, primary_key=True)
    balance = sa.Column(
        CompositeType(
            'money_type',
            [
                sa.Column('currency', CurrencyType),
                sa.Column('amount', sa.Integer)
            ]
        )
    )

复合材料阵列：

from sqlalchemy_utils import CompositeArray


class Account(Base):
    __tablename__ = 'account'
    id = sa.Column(sa.Integer, primary_key=True)
    balances = sa.Column(
        CompositeArray(
            CompositeType(
                'money_type',
                [
                    sa.Column('currency', CurrencyType),
                    sa.Column('amount', sa.Integer)
                ]
            )
        )
    )