使用原始 SQL 时在 SQLAlchemy 中反序列化 JSON [英] Deserializing JSON in SQLAlchemy when using raw SQL
问题描述
我有一个存储在文本列中的 JSON 表:
I have a table with JSON stored in a text column:
import json
from sqlalchemy import create_engine, Column, text, Integer, TEXT, TypeDecorator
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
engine = create_engine('sqlite:///:memory:')
engine.execute("create table t (t_id int not null primary key, attrs text not null)")
engine.execute("insert into t values (1, '{\"a\": 1, \"b\": 2}')")
Session = sessionmaker(bind=engine)
我在 SQLAlchemy 中定义了到这个表的映射,使用在编组 JSON 字符串":
I defined a mapping to this table in SQLAlchemy, using the custom type defined in the SQLAlchemy docs under "Marshal JSON Strings":
Base = declarative_base()
# http://docs.sqlalchemy.org/en/rel_1_1/core/custom_types.html#marshal-json-strings
class JSONEncodedDict(TypeDecorator):
impl = TEXT
def process_bind_param(self, value, dialect):
if value is not None:
value = json.dumps(value)
return value
def process_result_value(self, value, dialect):
if value is not None:
value = json.loads(value)
return value
class T(Base):
__tablename__ = 't'
t_id = Column(Integer, primary_key=True)
attrs = Column(JSONEncodedDict)
如果我查询所有 T
,attrs
会从 JSON 中反序列化:
If I query all T
s, attrs
gets deserialized from JSON:
session = Session()
t = session.query(T).first()
assert type(t.attrs) == dict, repr(t.attrs)
但是如果我使用文本查询/原始 SQL,它不会被反序列化:
But if I use a textual query / raw SQL, it isn't deserialized:
session = Session()
t = session.query(T).from_statement(text('select * from t')).first()
assert type(t.attrs) == dict, repr(t.attrs) # AssertionError: u'{"a": 1, "b": 2}'
使用原始 SQL 查询时,如何让 SQLAlchemy 反序列化 attrs
列?
How do I make SQLAlchemy deserialize the attrs
column when querying with raw SQL?
行为与其他数据库(MySQL、Postgres)相同.我使用的数据库 (MySQL 5.5) 不支持原生 JSON 类型,因此无法更改列类型.
The behavior is the same with other databases (MySQL, Postgres). The database I am using (MySQL 5.5) does not support native JSON types, so changing the column type is not an option.
推荐答案
你可以告诉 TextClause
(由 text()
) 使用 .columns()
:
You can tell TextClause
(produced by text()
) the column types using .columns()
:
from sqlalchemy import inspect
session = Session()
stmt = text('select * from t').columns(*inspect(T).columns)
t = session.query(T).from_statement(stmt).first()
assert type(t.attrs) == dict, repr(t.attrs)
或者,对于 SQLAlchemy<0.9,使用 typemap 参数:
Or, for SQLAlchemy<0.9, use the typemap argument:
from sqlalchemy import inspect
session = Session()
typemap = {c.name: c.type for c in inspect(T).columns}
stmt = text('select * from t', typemap=typemap)
t = session.query(T).from_statement(stmt).first()
assert type(t.attrs) == dict, repr(t.attrs)
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