python - Alembic 检测表已经存在，所以它试图再次创建它们

Question

我的动画表模型如下:数据库中没有测试列，我想用alembic更新它。

class Animation(Base):
    __tablename__="Animation"
    id=Column(Integer,primary_key=True,index=True,autoincrement=True)
    name=Column(VARCHAR(100))
    description=Column(VARCHAR(100))
    animation=Column(VARCHAR(100))
    created_at=Column(DateTime)
    updated_at=Column(DateTime)
    test=Column(DateTime)

但是 alembic 检测所有现有表并尝试重新创建它们。所以当我运行命令“alembic upgrade head”时它返回一个错误。它说该表已经存在。

当我运行自动生成命令时版本脚本如下:

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('Animation',
    sa.Column('id', sa.Integer(), autoincrement=True, nullable=False),
    sa.Column('name', sa.VARCHAR(length=100), nullable=True),
    sa.Column('description', sa.VARCHAR(length=100), nullable=True),
    sa.Column('animation', sa.VARCHAR(length=100), nullable=True),
    sa.Column('created_at', sa.DateTime(), nullable=True),
    sa.Column('updated_at', sa.DateTime(), nullable=True),
    sa.Column('test', sa.DateTime(), nullable=True),
    sa.PrimaryKeyConstraint('id')
    )
    op.create_index(op.f('ix_Animation_id'), 'Animation', ['id'], unique=False)
    op.create_table('Faq',
    sa.Column('id', sa.Integer(), autoincrement=True, nullable=False),
    sa.Column('title', sa.VARCHAR(length=100), nullable=True),
    sa.Column('description', sa.VARCHAR(length=100), nullable=True),
    sa.Column('animation_id', sa.Integer(), nullable=True),
    sa.Column('created_at', sa.DateTime(), nullable=True),
    sa.Column('updated_at', sa.DateTime(), nullable=True),
    sa.PrimaryKeyConstraint('id')
    )
    op.create_index(op.f('ix_Faq_id'), 'Faq', ['id'], unique=False)
    op.create_table('Service',
    sa.Column('id', sa.Integer(), autoincrement=True, nullable=False),
    sa.Column('plate', sa.VARCHAR(length=100), nullable=True),
    sa.Column('arrive_city', sa.VARCHAR(length=100), nullable=True),
    sa.Column('arrive_district', sa.VARCHAR(length=100), nullable=True),
    sa.Column('departure_time', sa.Time(), nullable=True),
    sa.Column('created_at', sa.DateTime(), nullable=True),
    sa.Column('updated_at', sa.DateTime(), nullable=True),
    sa.PrimaryKeyConstraint('id')
    )
    op.create_index(op.f('ix_Service_id'), 'Service', ['id'], unique=False)
    op.drop_index('ix_Service_id', table_name='service')
    op.drop_table('service')
    op.drop_index('ix_Animation_id', table_name='animation')
    op.drop_table('animation')
    op.drop_index('ix_Faq_id', table_name='faq')
    op.drop_table('faq')
    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    op.create_table('faq',
    sa.Column('id', mysql.INTEGER(display_width=11), autoincrement=True, nullable=False),
    sa.Column('title', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('description', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('animation_id', mysql.INTEGER(display_width=11), autoincrement=False, nullable=True),
    sa.Column('created_at', mysql.DATETIME(), nullable=True),
    sa.Column('updated_at', mysql.DATETIME(), nullable=True),
    sa.PrimaryKeyConstraint('id'),
    mysql_collate='utf8_turkish_ci',
    mysql_default_charset='utf8',
    mysql_engine='MyISAM'
    )
    op.create_index('ix_Faq_id', 'faq', ['id'], unique=False)
    op.create_table('animation',
    sa.Column('id', mysql.INTEGER(display_width=11), autoincrement=True, nullable=False),
    sa.Column('name', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('description', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('animation', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('created_at', mysql.DATETIME(), nullable=True),
    sa.Column('updated_at', mysql.DATETIME(), nullable=True),
    sa.PrimaryKeyConstraint('id'),
    mysql_collate='utf8_turkish_ci',
    mysql_default_charset='utf8',
    mysql_engine='MyISAM'
    )
    op.create_index('ix_Animation_id', 'animation', ['id'], unique=False)
    op.create_table('service',
    sa.Column('id', mysql.INTEGER(display_width=11), autoincrement=True, nullable=False),
    sa.Column('plate', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('arrive_city', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('arrive_district', mysql.VARCHAR(collation='utf8_turkish_ci', length=100), nullable=True),
    sa.Column('departure_time', mysql.TIME(), nullable=True),
    sa.Column('created_at', mysql.DATETIME(), nullable=True),
    sa.Column('updated_at', mysql.DATETIME(), nullable=True),
    sa.PrimaryKeyConstraint('id'),
    mysql_collate='utf8_turkish_ci',
    mysql_default_charset='utf8',
    mysql_engine='MyISAM'
    )
    op.create_index('ix_Service_id', 'service', ['id'], unique=False)
    op.drop_index(op.f('ix_Service_id'), table_name='Service')
    op.drop_table('Service')
    op.drop_index(op.f('ix_Faq_id'), table_name='Faq')
    op.drop_table('Faq')
    op.drop_index(op.f('ix_Animation_id'), table_name='Animation')
    op.drop_table('Animation')
    # ### end Alembic commands ###

我是 alembic 的新手，我找不到任何解决方案。

Answer 1

听起来您已经在数据库中创建了表，并且现在才开始使用 alembic，因为您需要添加一个新列。所以 alembic 假定它需要创建所有表。

要解决此问题，您可以:

• 删除旧的迁移脚本
• 备份你的数据库(只是预防措施)
• 做DELETE FROM alembic_version在你的数据库中，如果表存在
• 将代码恢复到添加新列之前的状态
• 生成一个迁移，记下引用(abc123ef 或类似的)
• 做alembic stamp <reference>
• 为新列添加代码
• 照常生成并运行 alembic 迁移

alembic stamp在数据库中设置先前迁移的引用，因此 alembic 知道从哪里开始。通过生成初始迁移和 stamp通过它，我们让 alembic 知道它只需要为新列运行迁移。

您可以简单地运行 alembic stamp head而不是生成和标记初始迁移，但我还没有对此进行测试。