Flask-Migrate Migration

  退出码 0
    Creating directory <实验目录>/fltmp/f74/migrations ...  done
    Creating directory <实验目录>/fltmp/f74/migrations/versions ...  done
    Generating <实验目录>/fltmp/f74/migrations/script.py.mako ...  done
    Generating <实验目录>/fltmp/f74/migrations/env.py ...  done
    Generating <实验目录>/fltmp/f74/migrations/README ...  done
    Generating <实验目录>/fltmp/f74/migrations/alembic.ini ...  done
    …(共 7 行)
  生成的文件: ['migrations/README', 'migrations/alembic.ini', 'migrations/env.py', 'migrations/script.py.mako']
  此时数据库里的表: None (还没有迁移,数据库文件都没创建)

  退出码 0
    Generating <实验目录>/fltmp/f74/migrations/versions/8cec42da86e2_create_user_table.py ...  done
    INFO  [alembic.autogenerate.compare.tables] Detected added table 'user'
  迁移脚本里的 upgrade()/downgrade()(节选):
    def upgrade():
        # ### commands auto generated by Alembic - please adjust! ###
        op.create_table('user',
        sa.Column('id', sa.Integer(), nullable=False),
        sa.Column('name', sa.String(length=50), nullable=False),
        sa.PrimaryKeyConstraint('id')
        )
        # ### end Alembic commands ###
    def downgrade():
        # ### commands auto generated by Alembic - please adjust! ###
        op.drop_table('user')
        # ### end Alembic commands ###
  revision / down_revision: 8cec42da86e2 / None
  执行 migrate 之后数据库里的表: ['alembic_version'] (migrate 只生成脚本)

  退出码 0
    INFO  [alembic.runtime.migration] Running upgrade  -> 8cec42da86e2, create user table
  数据库里的表: ['alembic_version', 'user']
  user 表的列: [('id', 'INTEGER', 1), ('name', 'VARCHAR(50)', 1)]
  alembic_version 里的值: [('8cec42da86e2',)]
  flask db current: ['8cec42da86e2 (head)']

  migrate: ["INFO  [alembic.autogenerate.compare.tables] Detected added table 'post'", "INFO  [alembic.autogenerate.compare.tables] Detected added column 'user.email'"]
  第二个迁移脚本 upgrade() 里的操作: ['create_table', 'batch_alter_table', 'add_column']
  downgrade() 里的操作: ['batch_alter_table', 'drop_column', 'drop_table']
  down_revision 指向第一个迁移: True
  upgrade 后表: ['alembic_version', 'post', 'user'] | user 的列: ['id', 'name', 'email']

  flask db history:
    8cec42da86e2 -> 51fc821dbe2a (head), add email and post
    <base> -> 8cec42da86e2, create user table
  downgrade 之后表: ['alembic_version', 'user'] | user 的列: ['id', 'name']

  upgrade() 里的操作: [('batch_alter_table', ''), ('', 'add_column'), ('', 'drop_column')]
  相关语句: ["batch_op.add_column(sa.Column('mail', sa.String(length=120), nullable=True))", "batch_op.drop_column('email')"]

  flask db heads: ['aaaa1', 'aaaa2']
  有两个 head 时 flask db upgrade → ERROR [flask_migrate] Error: Multiple head revisions are present for given argument 'head'; please specify a specific target revision, '<branchname>@h
  flask db merge → ['Generating <项目>/migrations/versions/1c8bb08ac9c6_merge_heads.py ...  done']
  合并后 heads 数: 1