Python學習筆記：Flask-Migrate基於model作upgrade的基本原理

時間 2019-11-05

標籤 python 學習筆記 flask migrate 基於 model upgrade 基本原理欄目 Python 简体版

原文原文鏈接

1）flask-migrate的官網： https://flask-migrate.readthedocs.io/en/latest/

2）獲取幫助，在pycharm的控制檯中輸入 flask db --help，或者flask db migrate --help，這樣就能夠了解各個命令的信息了

3）通常用法，

>flask db init

>flask db migrate

>flask db upgrade

後續對腳本有任何的修改，只要重複執行後兩句就能夠了。

4）測試1：添加一行數據，刪除email列，而後再加上

針對下面這個表：

1 class User(db.Model):
2     __tablename__ = 'user'
3     id = db.Column(db.Integer,primary_key=True)
4     username = db.Column(db.String(64),index=True,unique=True)
5     email = db.Column(db.String(120),index=True,unique=True)
6     password_hash = db.Column(db.String(128))
7  
8     def __repr__(self):
9         return '<用戶名:{}>'.format(self.username)

a）先經過以上3個命令建立表；

b）而後再數據庫中插入一條數據；

c）而後從models中把email列刪除，執行migrate ,updrade，此時發現，數據還在，只是列刪除了；

d）而後恢復email列，執行migrate，upgrade，此時發現，數據還在，增長了一個email的空列；

仔細觀察日誌，發現這個upgrade執行的是升級，而不是從新建立

INFO  [alembic.runtime.migration] Running upgrade 04a26df9c6d3 -> 04f13e3c2f7e, empty message

其中04a26df9c6d3_.py的內容爲：

 1 """empty message
 2 Revision ID: 04a26df9c6d3
 3 Revises: 4ed84444672c
 4 Create Date: 2018-08-29 07:14:44.779039
 5  """
 6 from alembic import op
 7 import sqlalchemy as sa
 8  
 9  
10 # revision identifiers, used by Alembic.
11 revision = '04a26df9c6d3'
12 down_revision = '4ed84444672c'
13 branch_labels = None
14 depends_on = None
15  
16  
17 def upgrade():
18     # ### commands auto generated by Alembic - please adjust! ###
19     op.drop_index('ix_user_email', table_name='user')
20     op.drop_column('user', 'email')
21     # ### end Alembic commands ###
22  
23  
24 def downgrade():
25     # ### commands auto generated by Alembic - please adjust! ###
26     op.add_column('user', sa.Column('email', sa.VARCHAR(length=120), autoincrement=False, nullable=True))
27     op.create_index('ix_user_email', 'user', ['email'], unique=True)
28     # ### end Alembic commands ###

04f13e3c2f7e_.py 的內容爲

 1 """empty message
 2  
 3 Revision ID: 04f13e3c2f7e
 4 Revises: 04a26df9c6d3
 5 Create Date: 2018-08-29 07:19:33.876815
 6  
 7 """
 8 from alembic import op
 9 import sqlalchemy as sa
10  
11  
12 # revision identifiers, used by Alembic.
13 revision = '04f13e3c2f7e'
14 down_revision = '04a26df9c6d3'
15 branch_labels = None
16 depends_on = None
17  
18  
19 def upgrade():
20     # ### commands auto generated by Alembic - please adjust! ###
21     op.add_column('user', sa.Column('email', sa.String(length=120), nullable=True))
22     op.create_index(op.f('ix_user_email'), 'user', ['email'], unique=True)
23     # ### end Alembic commands ###
24  
25  
26 def downgrade():
27     # ### commands auto generated by Alembic - please adjust! ###
28     op.drop_index(op.f('ix_user_email'), table_name='user')
29     op.drop_column('user', 'email')
30     # ### end Alembic commands ###

5）測試2：把user表刪除

a）若是隻執行flask db upgrade，則什麼都不執行

 
         (venv) D:\WORK\gitbase\HelloFlask>flask db upgrade 
        
         INFO [alembic.runtime.migration] Context impl PostgresqlImpl. 
        
         INFO [alembic.runtime.migration] Will assume transactional DDL.

b）執行flask db migrate，而後再執行flask db upgrade，則能夠從新建立表

經過migrate，程序會先比較本地的model和數據庫中實際的表，而後建立以下腳本 69f5e753ee6c_.py

 1 """empty message
 2  
 3 Revision ID: 69f5e753ee6c
 4 Revises: 04f13e3c2f7e
 5 Create Date: 2018-08-29 07:31:19.236320
 6  
 7 """
 8 from alembic import op
 9 import sqlalchemy as sa
10  
11  
12 # revision identifiers, used by Alembic.
13 revision = '69f5e753ee6c'
14 down_revision = '04f13e3c2f7e'
15 branch_labels = None
16 depends_on = None
17  
18  
19 def upgrade():
20     # ### commands auto generated by Alembic - please adjust! ###
21     op.create_table('user',
22     sa.Column('id', sa.Integer(), nullable=False),
23     sa.Column('username', sa.String(length=64), nullable=True),
24     sa.Column('email', sa.String(length=120), nullable=True),
25     sa.Column('password_hash', sa.String(length=128), nullable=True),
26     sa.PrimaryKeyConstraint('id')
27     )
28     op.create_index(op.f('ix_user_email'), 'user', ['email'], unique=True)
29     op.create_index(op.f('ix_user_username'), 'user', ['username'], unique=True)
30     # ### end Alembic commands ###
31  
32  
33 def downgrade():
34     # ### commands auto generated by Alembic - please adjust! ###
35     op.drop_index(op.f('ix_user_username'), table_name='user')
36     op.drop_index(op.f('ix_user_email'), table_name='user')
37     op.drop_table('user')
38     # ### end Alembic commands ###