【已解决】Flask-Migrate升级MySQL字段时能否重命名而非删除后新建

之前用Flask-Migrate去升级SQLAlchemy的数据库,底层是操作MySQL的数据库

但是有个问题

当更改了其中一个table的字段Column时,比如:

class Bill(db.Model):
    __tablename__ = ‘bills’
    disbursementFee = db.Column(db.Float, nullable=False, default = 0.0)

改为:

class Bill(db.Model):
    __tablename__ = ‘bills’
    advancedFee = db.Column(db.Float, nullable=False, default = 0.0)

把disbursementFee改为advancedFee

然后去运行:

(RunningFast) ➜  staging python db_manager.py db migrate -m "update Bill, from disbursementFee to advancedFee"

<div–<——————————————————————————

DEBUG in app [/root/RunningFast/staging/runningfast/app.py:86]:
app=<Flask ‘runningfast.app’>, server_port=21085, api=<flask_restful.Api object at 0x7f850afdbc90>, redis_store=<flask_redis.FlaskRedis object at 0x7f850d473310>, db=<SQLAlchemy engine=’mysql://runningfast:Jiandao123@localhost/runningfast_dev’>, server_mode=staging, server_type=develop, rq=<flask_rq2.app.RQ object at 0x7f850aff2110>, sockets=<flask_sockets.Sockets object at 0x7f850aff2490>

<div–<——————————————————————————

<div–<——————————————————————————

DEBUG in app [/root/RunningFast/staging/runningfast/app.py:181]:
API_VERSION=1.0, API_URL_PREFIX=/runningfast/api/v1.0, OPEN_API_URL_PREFIX=/runningfast/api/v1.0/open

<div–<——————————————————————————

INFO  [alembic.runtime.migration] Context impl MySQLImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
INFO  [alembic.autogenerate.compare] Detected added column ‘bills.advancedFee’
INFO  [alembic.autogenerate.compare] Detected added foreign key (errandorBillTaskId)(id) on table bills
INFO  [alembic.autogenerate.compare] Detected added foreign key (initiatorBillTaskId)(id) on table bills
INFO  [alembic.autogenerate.compare] Detected removed column ‘bills.disbursementFee’
INFO  [alembic.autogenerate.compare] Detected added foreign key (initiatorTaskId)(id) on table resources
INFO  [alembic.autogenerate.compare] Detected added foreign key (errandorTaskId)(id) on table resources
INFO  [alembic.autogenerate.compare] Detected added foreign key (errandorId)(id) on table tasks
INFO  [alembic.autogenerate.compare] Detected added foreign key (errandorEndLocationId)(id) on table tasks
INFO  [alembic.autogenerate.compare] Detected added foreign key (initiatorEndLocationId)(id) on table tasks
INFO  [alembic.autogenerate.compare] Detected added foreign key (initiatorStartLocationId)(id) on table tasks
INFO  [alembic.autogenerate.compare] Detected added foreign key (errandorStartLocationId)(id) on table tasks
INFO  [alembic.autogenerate.compare] Detected added foreign key (initiatorId)(id) on table tasks
INFO  [alembic.autogenerate.compare] Detected added foreign key (task_id)(id) on table tasks_promotions
INFO  [alembic.autogenerate.compare] Detected added foreign key (promotion_id)(id) on table tasks_promotions
INFO  [alembic.autogenerate.compare] Detected added foreign key (locationId)(id) on table users
  Generating /root/RunningFast/staging/migrations/versions/d48c252c778a_update_bill_from_disbursementfee_to_.py … done

后,去看生成的脚本

/Users/crifan/dev/dev_root/daryun/Projects/RunningFast/sourcecode/RunningFast-Server/migrations/versions/d48c252c778a_update_bill_from_disbursementfee_to_.py

中的是:

def upgrade():
    ### commands auto generated by Alembic – please adjust! ###
    op.add_column(‘bills’, sa.Column(‘advancedFee’, sa.Float(), nullable=False))
    op.create_foreign_key(None, ‘bills’, ‘tasks’, [‘errandorBillTaskId’], [‘id’])
    op.create_foreign_key(None, ‘bills’, ‘tasks’, [‘initiatorBillTaskId’], [‘id’])
    op.drop_column(‘bills’, ‘disbursementFee’)
    op.create_foreign_key(None, ‘resources’, ‘tasks’, [‘initiatorTaskId’], [‘id’])
    op.create_foreign_key(None, ‘resources’, ‘tasks’, [‘errandorTaskId’], [‘id’])
    op.create_foreign_key(None, ‘tasks’, ‘users’, [‘errandorId’], [‘id’])
    op.create_foreign_key(None, ‘tasks’, ‘locations’, [‘errandorEndLocationId’], [‘id’])
    op.create_foreign_key(None, ‘tasks’, ‘locations’, [‘initiatorEndLocationId’], [‘id’])
    op.create_foreign_key(None, ‘tasks’, ‘locations’, [‘initiatorStartLocationId’], [‘id’])
    op.create_foreign_key(None, ‘tasks’, ‘locations’, [‘errandorStartLocationId’], [‘id’])
    op.create_foreign_key(None, ‘tasks’, ‘users’, [‘initiatorId’], [‘id’])
    op.create_foreign_key(None, ‘tasks_promotions’, ‘tasks’, [‘task_id’], [‘id’])
    op.create_foreign_key(None, ‘tasks_promotions’, ‘promotions’, [‘promotion_id’], [‘id’])
    op.create_foreign_key(None, ‘users’, ‘locations’, [‘locationId’], [‘id’])
    ### end Alembic commands ###
def downgrade():
    ### commands auto generated by Alembic – please adjust! ###
    op.drop_constraint(None, ‘users’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks_promotions’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks_promotions’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks’, type_=’foreignkey’)
    op.drop_constraint(None, ‘tasks’, type_=’foreignkey’)
    op.drop_constraint(None, ‘resources’, type_=’foreignkey’)
    op.drop_constraint(None, ‘resources’, type_=’foreignkey’)
    op.add_column(‘bills’, sa.Column(‘disbursementFee’, mysql.FLOAT(), nullable=False))
    op.drop_constraint(None, ‘bills’, type_=’foreignkey’)
    op.drop_constraint(None, ‘bills’, type_=’foreignkey’)
    op.drop_column(‘bills’, ‘advancedFee’)
    ### end Alembic commands ###

即,对于:

upgrade

op.drop_column(‘bills’, ‘disbursementFee’)

op.add_column(‘bills’, sa.Column(‘advancedFee’, sa.Float(), nullable=False))

即:drop旧的字段,add新的字段,则旧的字段中的数据:

在drop后,就都丢失了。。。

所以希望是:

能否有个

op.rename_column

可以把之前的disbursementFee改为新的advancedFee

flask-migrate rename column

renaming columns – not dropping old and creating new · Issue #30 · miguelgrinberg/Flask-Migrate

去查查看,是否有个:

op.alter_column

Change from Integer to String not detected. · Issue #24 · miguelgrinberg/Flask-Migrate

No changes detected in Alembic autogeneration of migrations with Flask-SQLAlchemy – Stack Overflow

python – How to write alter column name migrations with sqlalchemy-migrate? – Stack Overflow

postgresql – Flask-migrate and changing column type – Stack Overflow

是有个:

op.alter_column

但是要去搞清楚,此处语法如何写。

alembic – can not rename column using alter_column – Stack Overflow

sqlite是不支持列改名的

-》MySQL应该是支持的。

Welcome to Flask-Migrate’s documentation! — Flask-Migrate documentation

结果没有找到语法。

从:

from alembic import op

看到:

此处的op是alembic,所以alter_column也应该是去找alembic

alembic alter_column

alembic alter_column rename

Operation Reference — Alembic 0.8.9 documentation

alter_column(table_name, column_name, nullable=None, server_default=False, new_column_name=None, type_=None, existing_type=None, existing_server_default=False, existing_nullable=None, schema=None, **kw)
Issue an “alter column” instruction using the current migration context.
Generally, only that aspect of the column which is being changed, i.e. name, type, nullability, default, needs to be specified. Multiple changes can also be specified at once and the backend should “do the right thing”, emitting each change either separately or together as the backend allows.
MySQL has special requirements here, since MySQL cannot ALTER a column without a full specification. When producing MySQL-compatible migration files, it is recommended that the existing_type, existing_server_default, and existing_nullable parameters be present, if not being altered.
Type changes which are against the SQLAlchemy “schema” types Boolean and Enum may also add or drop constraints which accompany those types on backends that don’t support them natively. The existing_type argument is used in this case to identify and remove a previous constraint that was bound to the type object.
Parameters:     
table_name – string name of the target table.
column_name – string name of the target column, as it exists before the operation begins.
nullable – Optional; specify True or False to alter the column’s nullability.
server_default – Optional; specify a string SQL expression, text(), or DefaultClause to indicate an alteration to the column’s default value. Set to None to have the default removed.
new_column_name – Optional; specify a string name here to indicate the new name within a column rename operation.
type_ – Optional; a TypeEngine type object to specify a change to the column’s type. For SQLAlchemy types that also indicate a constraint (i.e. Boolean, Enum), the constraint is also generated.
autoincrement – set the AUTO_INCREMENT flag of the column; currently understood by the MySQL dialect.
existing_type – Optional; a TypeEngine type object to specify the previous type. This is required for all MySQL column alter operations that don’t otherwise specify a new type, as well as for when nullability is being changed on a SQL Server column. It is also used if the type is a so-called SQLlchemy “schema” type which may define a constraint (i.e. Boolean, Enum), so that the constraint can be dropped.
existing_server_default – Optional; The existing default value of the column. Required on MySQL if an existing default is not being changed; else MySQL removes the default.
existing_nullable – Optional; the existing nullability of the column. Required on MySQL if the existing nullability is not being changed; else MySQL sets this to NULL.
existing_autoincrement – Optional; the existing autoincrement of the column. Used for MySQL’s system of altering a column that specifies AUTO_INCREMENT.
schema –
Optional schema name to operate within. To control quoting of the schema outside of the default behavior, use the SQLAlchemy construct quoted_name.
New in version 0.7.0: ‘schema’ can now accept a quoted_name construct.
postgresql_using¶ –
String argument which will indicate a SQL expression to render within the Postgresql-specific USING clause within ALTER COLUMN.
New in version 0.8.8.

可以看到有:column_name和new_column_name

应该就是rename了。

[python]通过 alembic 重命名表列名(Model字段名) – Mozillazg’s Blog

from sqlalchemy.dialects import mysql
def upgrade():
    ### commands auto generated by Alembic – please adjust! ###
    # 把 user 表里的 name 列重命名为 username
    op.alter_column(‘user’, ‘name’, new_column_name=’username’,
                    existing_type=mysql.VARCHAR(length=20))
    ### end Alembic commands ###
def downgrade():
    ### commands auto generated by Alembic – please adjust! ###
    op.alter_column(‘user’, ‘username’, new_column_name=’name’,
                    existing_type=mysql.VARCHAR(length=20))
    ### end Alembic commands ###

alembic.op.alter_column – Nullege Python Samples

    op.drop_constraint(‘foldersync_ibfk_1’, ‘foldersync’, type_=’foreignkey’)
    op.alter_column(‘foldersync’, ‘imapaccount_id’,
                    new_column_name=’account_id’, existing_type=sa.Integer(),
                    existing_nullable=False)

结果:

【已解决】Flask-Migrate内部利用Alembic中升级数据库时出错:AttributeError float object has no attribute _compiler_dispatch

然后去看对应的数据库的字段,是否真的改过来了,且原先的数据保留下来了:

结论是可以的。

【总结】

Flask-Migrate中去升级数据库字段,底层是调用Alembic去实现的。

而对于重命名Column列名的话,对应的函数是:alter_column

具体用法详见官网文档:

Operation Reference — Alembic 0.8.9 documentation

其中解释的也很清楚了:

一般来说,只需要传入需要alter修改的参数,比如表名,列名,是否为null,默认值,等等,即可。

但是MYSQL比较特殊,没有完整的参数的话,是不支持修改列名的

-》所以只能传入完整的参数了。。

-》所以修改列名,推荐同时把对应的参数传递上:

existing_type, existing_server_default, and existing_nullable

-》

但是此处,如果传了existing_server_default,则会导致出错:

【已解决】Flask-Migrate内部利用Alembic中升级数据库时出错:AttributeError float object has no attribute _compiler_dispatch

然后不传existing_server_default,用:

from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import mysql
def upgrade():
    ### commands auto generated by Alembic – please adjust! ###
    # op.add_column(‘bills’, sa.Column(‘advancedFee’, sa.Float(), nullable=False))
    op.alter_column(‘bills’,
                    ‘disbursementFee’,
                    new_column_name=’advancedFee’,
                    existing_type=sa.Float,
                    existing_nullable=False)
    #op.drop_column(‘bills’, ‘disbursementFee’)
    ### end Alembic commands ###
def downgrade():
    ### commands auto generated by Alembic – please adjust! ###
    # op.add_column(‘bills’, sa.Column(‘disbursementFee’, mysql.FLOAT(), nullable=False))
    # op.drop_column(‘bills’, ‘advancedFee’)
    op.alter_column(‘bills’,
                    ‘advancedFee’,
                    new_column_name=’disbursementFee’,
                    existing_type=sa.Float,
                    existing_nullable=False)
    ### end Alembic commands ###

就可以了。

然后就可以正常升级了:

python db_manager.py db upgrade 



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