SQLAlchemy如何從Session查詢對象獲取響應？

-1

我已經通過了SQLAlchemy ORM tutorial，現在正在將它調整到我自己的數據庫。我遇到了Postgres方言的問題，我試圖查詢Session對象，但是我沒有收到結果。我相信我錯過了一些東西，並且可以利用一些方向來實現這個目標，或者至少我應該研究什麼。感謝您的幫助。SQLAlchemy如何從Session查詢對象獲取響應？

代碼

import sqlalchemy 
from sqlalchemy import create_engine, ForeignKey, Column, INTEGER 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy.dialects.postgresql import TEXT, NUMERIC, TIMESTAMP 
from sqlalchemy.orm import sessionmaker 

# CONNECTING 
# create an instance of Engine, represents core interface to the db 
engine = create_engine('postgresql://user:[email protected]:port/db', echo=True) 

# DECLARE A MAPPING 
# instantiate the Declarative base class for a catalog of classes & tables 
# relative to the base class. 
Base = declarative_base() 

# map a table to a class by inheriting base class via declarative_base 
class History_1m(Base): 
    __tablename__ = 'history_1m' 

    id = Column(INTEGER, primary_key=True, autoincrement=True) 
    name = Column(TEXT) 
    symbol = Column(TEXT) 
    ask = Column(NUMERIC) 
    bid = Column(NUMERIC) 

# CREATE A SCHEMA 
# using the engine, create our table via a method of the MetaData registry 
Base.metadata.create_all(engine) 

# CREATE AN INSTANCE OF MAPPED CLASS 
# instantiate an instance of the User class and generate attribute values 
symbol_data = History_1m() 

# CREATING A SESSION 
# define a Session class to talk with our db 
Session = sessionmaker(bind=engine) 
session = Session() 
# in case of no engine yet, Session = sessionmaker() is acceptable 
# to talk to the db you should use session = Session each time 

# query the Session to verify the instance is pending 
symbol = 'AAPL' 
recent_symbol = session.query(History_1m).filter_by(symbol=symbol).first() 

# print the contents of our_user, ed_user is our_user via identity map 
print('\n> Do we have a symbol entry?\n', recent_symbol) 
for row in session.query(History_1m).order_by(History_1m.id): 
    print(row.name, row.symbol, row.ask, row.bid)

回溯

Microsoft Corporation MSFT 65.52 65.51 
Adobe Systems Incorporated ADBE 131.85 131.83 
Cytori Therapeutics Inc CYTX 1.04 1.03 
Whole Foods Market, Inc. WFM 35.58 35.57 
None None None None

進程退出代碼爲0

來源

2017-04-20 Liquidgenius

你在哪裏讓你'NameError'目前還不清楚。你的例子不應該產生它。請同時包含一個[可驗證的示例]（http://stackoverflow.com/help/mcve）以及您獲得的回溯。或者重寫你的標題和問題。至於獲得'None'，你確定你的數據庫包含一個'name ='AAPL'的行，或者你的意思是'filter_by（symbol = symbol）'？你是否連接到正確的數據庫？ –

嗨Ilja，我重新命名了這個問題，並將輸出部分改爲Traceback。我知道我正在連接到正確的數據庫。我相信你是正確的，我正在尋找一個符號而不是名稱字段。 – Liquidgenius

在將symbol_data添加到會話並查詢它之前，是否必須爲symbol_data創建映射類的實例？如果是這樣，有沒有一種簡單的方法可以將它映射到表中的所有列，而不是在symbol_data對象中隱式定義它們？（如果這甚至是問題。） – Liquidgenius

我沒有得到的代碼工作完成。我沒有正確格式化會話上的查詢對象。

CODE

import sqlalchemy 
from sqlalchemy import create_engine, ForeignKey, Column, INTEGER 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy.dialects.postgresql import TEXT, NUMERIC, TIMESTAMP 
from sqlalchemy.orm import sessionmaker 

# CONNECTING 
# create an instance of Engine, represents core interface to the db 
engine = create_engine('postgresql://user:[email protected]:pport/database', echo=True) 

# DECLARE A MAPPING 
# instantiate the Declarative base class for a catalog of classes & tables 
# relative to the base class. 
Base = declarative_base() 

# map a table to a class by inheriting base class via declarative_base 
class History_1m(Base): 
    __tablename__ = 'history_1m' 

    id = Column(INTEGER, primary_key=True, autoincrement=True) 
    name = Column(TEXT) 
    symbol = Column(TEXT) 
    ask = Column(NUMERIC) 
    bid = Column(NUMERIC) 

# CREATE A SCHEMA 
# using the engine, create our table via a method of the MetaData registry 
Base.metadata.create_all(engine) 

# CREATING A SESSION 
# define a Session class to talk with our db 
Session = sessionmaker(bind=engine) 
# in case of no engine yet, Session = sessionmaker() is acceptable 
# to talk to the db you should use session = Session each time 

# query the Session for the first symbol entry 
session = Session() 
symbol = 'AAPL' 
recent_symbol = session.query(History_1m).filter_by(symbol=symbol).first() 

# print the contents of the response via identity map 
print('\n> Do we have a symbol entry?\n', recent_symbol.name, recent_symbol.symbol, 
     recent_symbol.ask, recent_symbol.bid)

TRACEBACK

C:\Users\User\Anaconda2\envs\python36_learning\python.exe D:/tech_indicators/sqla_orm_adapt.py 
2017-04-20 12:45:33,470 INFO sqlalchemy.engine.base.Engine select version() 
2017-04-20 12:45:33,470 INFO sqlalchemy.engine.base.Engine {} 
2017-04-20 12:45:33,471 INFO sqlalchemy.engine.base.Engine select current_schema() 
2017-04-20 12:45:33,471 INFO sqlalchemy.engine.base.Engine {} 
2017-04-20 12:45:33,472 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1 
2017-04-20 12:45:33,472 INFO sqlalchemy.engine.base.Engine {} 
2017-04-20 12:45:33,473 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1 
2017-04-20 12:45:33,473 INFO sqlalchemy.engine.base.Engine {} 
2017-04-20 12:45:33,473 INFO sqlalchemy.engine.base.Engine show standard_conforming_strings 
2017-04-20 12:45:33,473 INFO sqlalchemy.engine.base.Engine {} 
2017-04-20 12:45:33,474 INFO sqlalchemy.engine.base.Engine select relname from pg_class c join pg_namespace n on n.oid=c.relnamespace where pg_catalog.pg_table_is_visible(c.oid) and relname=%(name)s 
2017-04-20 12:45:33,474 INFO sqlalchemy.engine.base.Engine {'name': 'history_1m'} 
2017-04-20 12:45:33,476 INFO sqlalchemy.engine.base.Engine BEGIN (implicit) 
2017-04-20 12:45:33,476 INFO sqlalchemy.engine.base.Engine SELECT history_1m.id AS history_1m_id, history_1m.name AS history_1m_name, history_1m.symbol AS history_1m_symbol, history_1m.ask AS history_1m_ask, history_1m.bid AS history_1m_bid 
FROM history_1m 
WHERE history_1m.symbol = %(symbol_1)s 
LIMIT %(param_1)s 
2017-04-20 12:45:33,477 INFO sqlalchemy.engine.base.Engine {'symbol_1': 'AAPL', 'param_1': 1} 

> Do we have a symbol entry? 
Apple Inc. AAPL 141.08 141.07 

Process finished with exit code 0

來源

2017-04-20 19:53:55 Liquidgenius

SQLAlchemy如何從Session查詢對象獲取響應？

回答

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