請問Sqlalchemy會自動爲外鍵創建索引嗎？

Question

我在MYSQL中使用MyISAM引擎。我發現表中的外鍵已被自動創建索引。 Sqlalchemy或MYSQL的行爲是？我不需要外鍵的索引。我該怎麼辦？定義列時添加參數索引= False？

我的代碼：

class A(Base): 
    __tablename__ = "a" 
    a_id = Column(BigInteger, primary_key=True, autoincrement=True) 

class B(Base): 
    __tablename__ = "b" 
    b_id = Column(BigInteger, primary_key=True, autoincrement=True) 
    a_id = Column(BigInteger, ForeignKey(A.a_id)) 

我發現在B中A_ID指數已經自動創建。這是對的嗎？ 如果我想刪除這樣的索引，我可以這樣做嗎？

class B(Base): 
    __tablename__ = "b" 
    b_id = Column(BigInteger, primary_key=True, autoincrement=True) 
    a_id = Column(BigInteger, ForeignKey(A.a_id), index=False) 

Answer 1

我在我的本地機器中創建了您的模型，並且我沒有在外鍵上找到任何索引。

我用

from sqlalchemy import create_engine 

engine = create_engine('mysql://test:test@localhost/test1', echo=True) 

from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy import Column, Integer, String, Date, Text, BigInteger, ForeignKey 
from sqlalchemy.orm.attributes import InstrumentedAttribute 


Base = declarative_base() 


class A(Base): 
    __tablename__ = "a" 
    a_id = Column(BigInteger, primary_key=True, autoincrement=True) 

class B(Base): 
    __tablename__ = "b" 
    b_id = Column(BigInteger, primary_key=True, autoincrement=True) 
    a_id = Column(BigInteger, ForeignKey(A.a_id)) 

Base.metadata.create_all(engine) 

和背景日誌。

2012-02-24 09:39:24,249 INFO sqlalchemy.engine.base.Engine SELECT DATABASE() 
2012-02-24 09:39:24,249 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,254 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'character_set%%' 
2012-02-24 09:39:24,254 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,277 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'lower_case_table_names' 
2012-02-24 09:39:24,277 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,288 INFO sqlalchemy.engine.base.Engine SHOW COLLATION 
2012-02-24 09:39:24,289 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,292 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode' 
2012-02-24 09:39:24,292 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,293 INFO sqlalchemy.engine.base.Engine DESCRIBE `a` 
2012-02-24 09:39:24,293 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,321 INFO sqlalchemy.engine.base.Engine ROLLBACK 
2012-02-24 09:39:24,322 INFO sqlalchemy.engine.base.Engine DESCRIBE `b` 
2012-02-24 09:39:24,322 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,323 INFO sqlalchemy.engine.base.Engine ROLLBACK 
2012-02-24 09:39:24,324 INFO sqlalchemy.engine.base.Engine 
CREATE TABLE a (
    a_id BIGINT NOT NULL AUTO_INCREMENT, 
    PRIMARY KEY (a_id) 
) 


2012-02-24 09:39:24,324 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,590 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-02-24 09:39:24,591 INFO sqlalchemy.engine.base.Engine 
CREATE TABLE b (
    b_id BIGINT NOT NULL AUTO_INCREMENT, 
    a_id BIGINT, 
    PRIMARY KEY (b_id), 
    FOREIGN KEY(a_id) REFERENCES a (a_id) 
) 


2012-02-24 09:39:24,591 INFO sqlalchemy.engine.base.Engine() 
2012-02-24 09:39:24,762 INFO sqlalchemy.engine.base.Engine COMMIT 

我還要檢查在MySQL中創建表的語句a和b。

mysql> show create table a; 
+-------+-------------------------------------------------------------------------------------------------------------------------------+ 
| Table | Create Table                             | 
+-------+-------------------------------------------------------------------------------------------------------------------------------+ 
| a  | CREATE TABLE `a` (
    `a_id` bigint(20) NOT NULL AUTO_INCREMENT, 
    PRIMARY KEY (`a_id`) 
) ENGINE=InnoDB DEFAULT CHARSET=latin1 | 
+-------+-------------------------------------------------------------------------------------------------------------------------------+ 
1 row in set (0.00 sec) 

mysql> show create table b; 
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 
| Table | Create Table                                                             | 
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 
| b  | CREATE TABLE `b` (
    `b_id` bigint(20) NOT NULL AUTO_INCREMENT, 
    `a_id` bigint(20) DEFAULT NULL, 
    PRIMARY KEY (`b_id`), 
    KEY `a_id` (`a_id`), 
    CONSTRAINT `b_ibfk_1` FOREIGN KEY (`a_id`) REFERENCES `a` (`a_id`) 
) ENGINE=InnoDB DEFAULT CHARSET=latin1 | 
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 
1 row in set (0.00 sec) 

索引只在主鍵不在外鍵上。

請在你的機器上試試這個，如果你發現你的機器在表b的外鍵上創建索引，那麼發佈你創建的日誌和模型就像我在這個答案中寫的那樣。

希望這會解決您的問題。

Answer 2

拉法達，你是不對的。表b中的KEY a_id（a_id）清楚地顯示了在外鍵字段上的索引。這是InnoDB的的行爲 - 如果這樣的指標尚不它會自動在一個外鍵關係建立在字段的索引存在：

http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html

Answer 3

這是MySQL的behavior，這是正確的MySQL。你應該調和這個事實。至少我不知道如何擺脫外鍵的索引。

定義列時添加param index = False？

嗯，也許...我會試試看。