I had a SQLAlchemy model like -
class UserFavPlace(db.Model):
# This model stores the feedback from the user whether he has
# faved a place or not
__tablename__ = u'user_fav_places'
id = db.Column(db.Integer, primary_key = True)
public_place_id = db.Column(db.Integer, db.ForeignKey(u'public_places.id'))
user_id = db.Column(db.Integer, db.ForeignKey(u'users.user_id'))
fav = db.Column(db.Boolean)
updated_time = db.Column(db.DateTime)
place = relationship(u'PublicPlace', backref = u'user_fav_places')
user = relationship(u'User', backref = u'user_fav_places')
And then I changed this model to the following -
class UserFavPlace(db.Model):
# This model stores the feedback from the user whether he has
# faved a place or not
__tablename__ = u'user_fav_places'
public_place_id = db.Column(db.Integer, db.ForeignKey(u'public_places.id'),
primary_key = True)
user_id = db.Column(db.Integer, db.ForeignKey(u'users.user_id'),
primary_key = True)
fav = db.Column(db.Boolean)
updated_time = db.Column(db.DateTime)
place = relationship(u'PublicPlace', backref = u'user_fav_places')
user = relationship(u'User', backref = u'user_fav_places')
However, Alembic is not generating the correct upgrade and downgrade statements. Seems like it is not adding the newly introduced primary key constraints.
def upgrade():
### commands auto generated by Alembic - please adjust! ###
op.drop_column('user_fav_places', 'id')
### end Alembic commands ###
def downgrade():
### commands auto generated by Alembic - please adjust! ###
op.add_column('user_fav_places', sa.Column('id', mysql.INTEGER(display_width=11), nullable=False))
### end Alembic commands ###
I am not sure on how to add this.
I find the autogeneration to be pretty bad about detecting primary/foreign key changes. Which is okay, usually you want to customize those anyway.
I haven't created composite primary keys, but it looks like this should work based on the doc:
http://alembic.zzzcomputing.com/en/latest/ops.html#alembic.operations.Operations.create_primary_key
op.create_primary_key(
"pk_user_fav_places", "user_fav_places",
["public_place_id", "user_id"]
)
However, you might run into a different problem, which I wrote up here: Adding primary key to existing MySQL table in alembic
This might have been fixed in more recent versions of alembic, but it may not let you create primary keys on existing tables (see the answer to above for why). If that happens, you can just craft the SQL yourself and run it with op.execute.
Hope that helps!
Related
Hello I have little problem,So need Help to connect two tables in database. I used ORM in python and I know how to connect it in main.py file.But I decided to make one file per table,so when i want to use foreign key it say's error. Here is the code which i used for connection two tables:
engine = create_engine('mysql+pymysql://root:#localhost/popis?charset=utf8mb4', echo=False)
Session = sessionmaker(bind=engine)
session = Session()
Base = declarative_base()
class Stanovnik(Base):
__tablename__ = "stanovnik"
id = Column(Integer, primary_key=True)
ime = Column(String(20))
prezime = Column(String(50))
ratni_staz = Column(Integer)
godine = Column(Integer)
broj_clanova=Column(Integer)
sifra_adrese = Column(Integer,ForeignKey(adresa.sifra_adrese))
sifra_zene = Column(Integer,ForeignKey(zena.sifra_zene))
sifra_ostali = Column(Integer,ForeignKey(ostali.sifra_ostali))
Base.metadata.create_all(engine)
I tried every method for sql but one thing is missing I think.
I'm having difficulties in relationships. I have users and roles and defined model and schema for them.
the problem is when I try to add a new user with a previously defined role (I have its ID and name)it will try to update/insert the role table by the value the user specifies. but I only want to select from roles and specify that as a user role and not updating the role table(if role not found return error).
what I want to achieve is how to limit SQLalchemy in updating related tables by the value that the user specifies.
here is my models:
class User(db.Model):
"""user model
"""
__tablename__ = 'user'
id = db.Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4, unique=True, nullable=False)
username = db.Column(db.String(40), unique=True, nullable=False)
password = db.Column(db.String(255), nullable=False)
role_id = db.Column(UUID(as_uuid=True), db.ForeignKey('role.id') , nullable=False)
class Role(db.Model):
"""role model
"""
__tablename__ = 'role'
id = db.Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4, unique=True, nullable=False)
name = db.Column(db.String(40), unique=True, nullable=False)
perm_add = db.Column(db.Boolean, default=False)
perm_edit = db.Column(db.Boolean, default=False)
perm_del = db.Column(db.Boolean, default=False)
here is the schema that I defined:
class UserSchema(ma.SQLAlchemyAutoSchema):
password = ma.String(load_only=True, required=True)
email = ma.String(required=True)
role = fields.Nested("RoleSchema", only=("id", "name"), required=True)
class Meta:
model = User
sqla_session = db.session
load_instance = True
and I grab user input which is checked by schema and commit it to DB.
schema = UserSchema()
user = schema.load(request.json)
db.session.add(user)
try:
db.session.commit()
the point is here I could not change anything regarding role name or ID as it seems it is changed by schema even before applying to DB (I mean request.json)
In my example, I am using the additional webargs library. It facilitates validation on the server side and enables clean notation. Since marschmallow is based on webargs anyway, I think the addition makes sense.
I have based myself on your specifications. Depending on what you intend to do further, you may need to make adjustments.
I added a relationship to the user model to make the role easier to use.
class User(db.Model):
"""user model"""
# ...
# The role is mapped by sqlalchemy using the foreign key
# as an object and can be reached via a virtual relationship.
role = db.relationship('Role')
I have allowed the foreign key as a query parameter in the schema and limited the nested schema to the output. The email is assigned to the username.
class RoleSchema(ma.SQLAlchemyAutoSchema):
class Meta:
model = Role
load_instance = True
class UserSchema(ma.SQLAlchemyAutoSchema):
# The entry of the email is converted into a username.
username = ma.String(required=True, data_key='email')
password = ma.String(required=True, load_only=True)
# The foreign key is only used here for loading.
role_id = ma.Integer(required=True, load_only=True)
# The role is dumped with a query.
role = ma.Nested("RoleSchema", only=("id", "name"), dump_only=True)
class Meta:
model = User
load_instance = True
include_relationships = True
It is now possible to query the role from the database and react if it does not exist. The database table for the roles is no longer updated automatically.
from flask import abort
from sqlalchemy.exc import SQLAlchemyError
from webargs.flaskparser import use_args, use_kwargs
# A schema-compliant input is expected as JSON
# and passed as a parameter to the function.
#blueprint.route('/users/', methods=['POST'])
#use_args(UserSchema(), location='json')
def user_new(user):
# The role is queried from the database and assigned to the user object.
# If not available, 404 Not Found is returned.
user_role = Role.query.get_or_404(user.role_id)
user.role = user_role
# Now the user can be added to the database.
db.session.add(user)
try:
db.session.commit()
except SQLAlchemyError as exc:
# If an error occurs while adding to the database,
# 422 Unprocessable Entity is returned
db.session.rollback()
abort(422)
# Upon successful completion, the new user is returned
# with the status code 201 Created.
user_schema = UserSchema()
user_data = user_schema.dump(user)
return jsonify(data=user_data), 201
I am trying to get SQLAlchemy to let my database's foreign keys "on delete cascade" do the cleanup on the association table between two objects. I have setup the cascade and passive_delete options on the relationship as seems appropriate from the docs. However, when a related object is loaded into the collection of a primary object and the primary object is deleted from the session, then SQLAlchemy issues a delete statement on the secondary table for the record relating the primary and secondary objects.
For example:
import logging
import sqlalchemy as sa
import sqlalchemy.ext.declarative as sadec
import sqlalchemy.orm as saorm
engine = sa.create_engine('sqlite:///')
engine.execute('PRAGMA foreign_keys=ON')
logging.basicConfig()
_logger = logging.getLogger('sqlalchemy.engine')
meta = sa.MetaData(bind=engine)
Base = sadec.declarative_base(metadata=meta)
sess = saorm.sessionmaker(bind=engine)
session = sess()
blog_tags_table = sa.Table(
'blog_tag_map',
meta,
sa.Column('blog_id', sa.Integer, sa.ForeignKey('blogs.id', ondelete='cascade')),
sa.Column('tag_id', sa.Integer, sa.ForeignKey('tags.id', ondelete='cascade')),
sa.UniqueConstraint('blog_id', 'tag_id', name='uc_blog_tag_map')
)
class Blog(Base):
__tablename__ = 'blogs'
id = sa.Column(sa.Integer, primary_key=True)
title = sa.Column(sa.String, nullable=False)
tags = saorm.relationship('Tag', secondary=blog_tags_table, passive_deletes=True,
cascade='save-update, merge, refresh-expire, expunge')
class Tag(Base):
__tablename__ = 'tags'
id = sa.Column(sa.Integer, primary_key=True)
label = sa.Column(sa.String, nullable=False)
meta.create_all(bind=engine)
blog = Blog(title='foo')
blog.tags.append(Tag(label='bar'))
session.add(blog)
session.commit()
# sanity check
assert session.query(Blog.id).count() == 1
assert session.query(Tag.id).count() == 1
assert session.query(blog_tags_table).count() == 1
_logger.setLevel(logging.INFO)
session.commit()
# make sure the tag is loaded into the collection
assert blog.tags[0]
session.delete(blog)
session.commit()
_logger.setLevel(logging.WARNING)
# confirm check
assert session.query(Blog.id).count() == 0
assert session.query(Tag.id).count() == 1
assert session.query(blog_tags_table).count() == 0
The above code will produce DELETE statements as follows:
DELETE FROM blog_tag_map WHERE
blog_tag_map.blog_id = ? AND blog_tag_map.tag_id = ?
DELETE FROM blogs WHERE blogs.id = ?
Is there a way to setup the relationship so that no DELETE statement for blog_tag_map is issued? I've also tried setting passive_deletes='all' with the same results.
Here, the “related object” is not being deleted. That would be “tags”. The blog_tags_table is not an object, it is a many-to-many table. Right now the passive_deletes='all' option is not supported for many-to-many, that is, a relationship that includes "secondary". This would be an acceptable feature add but would require development and testing efforts.
Applying viewonly=True to the relationship() would prevent any changes from affecting the many-to-many table. If the blog_tags_table is otherwise special, then you'd want to use the association object pattern to have finer grained control.
I'm using alembic to maintain my tables. At the same time, I update my models using the declarative way.
This is one the alembic's table:
op.create_table(
'groups',
Column('id', Integer, Sequence('group_id_seq'), primary_key=True),
Column('name', Unicode(50)),
Column('description', Unicode(250)),
)
And the model is like the following:
class Group(Base):
__tablename__ = 'groups'
id = Column(Integer, Sequence('group_id_seq'), primary_key=True)
name = Column(Unicode(50))
description = Column(Unicode(250))
def __init__(self, name, description):
self.description = description
self.name = name
You can see, I'm using the Sequence in both the alembic migration and in the declarative model.
But I have noticed that when using PostgreSQL (v9.1) no sequences are created by alembic, and so the models fail to create instances since they will use the nextval(<sequence name>) clause.
So, how can I create my alembic migrations so that the sequences are truly generated in postgresql?
Just add following to your model:
field_seq = Sequence('groups_field_seq')
field = Column(Integer, field_seq, server_default=field_seq.next_value())
And add following to your migration file (before creating table):
from sqlalchemy.schema import Sequence, CreateSequence
op.execute(CreateSequence(Sequence('groups_field_seq')))
Found a hint at https://bitbucket.org/zzzeek/alembic/issue/60/autogenerate-for-sequences-as-well-as#comment-4100402
Following the CreateSequence found in the previous link I still have to jump through several hoops to make my migrations works in SQLite and PostgreSQL. Currently I have:
def dialect_supports_sequences():
return op._proxy.migration_context.dialect.supports_sequences
def create_seq(name):
if dialect_supports_sequences():
op.execute(CreateSequence(Sequence(name)))
And then call the create_seq whenever I need it.
Is this the best practice?
Not sure if I got your question right but as nobody else chose to answer, here is how I get perfectly normal ids:
Alembic:
op.create_table('event',
sa.Column('id', sa.INTEGER(), autoincrement=True, nullable=False),
The class:
class Event(SQLADeclarativeBase):
__tablename__ = 'event'
id = Column(Integer, primary_key = True)
I ran into this same issue recently and here is how i solved it.
op.execute("create sequence SEQUENCE_NAME")
I ran the above command inside the upgrade function and for the downgrade run the below code inside the downgrade function respectively.
op.execute("drop sequence SEQUENCE_NAME")
I have some code here. I recently added this root_id parameter. The goal of that is to let me determine whether a File belongs to a particular Project without having to add a project_id FK into File (which would result in a model cycle.) Thus, I want to be able to compare Project.directory to File.root. If that is true, File belongs to Project.
However, the File.root attribute is not being autogenerated for File. My understanding is that defining a FK foo_id into table Foo implicit creates a foo attribute to which you can assign a Foo object. Then, upon session flush, foo_id is properly set to the id of the assigned object. In the snippet below that is clearly being done for Project.directory, but why not for File.root?
It definitely seems like it has to do with either 1) the fact that root_id is a self-referential FK or 2) the fact that there are several self-referential FKs in File and SQLAlchemy gets confused.
Things I've tried.
Trying to define a 'root' relationship() - I think this is wrong, this should not be represented by a join.
Trying to define a 'root' column_property() - allows read access to an already set root_id property, but when assigning to it, does not get reflected back to root_id
How can I do what I'm trying to do? Thanks!
from sqlalchemy import create_engine, Column, ForeignKey, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import backref, relationship, scoped_session, sessionmaker, column_property
Base = declarative_base()
engine = create_engine('sqlite:///:memory:', echo=True)
Session = scoped_session(sessionmaker(bind=engine))
class Project(Base):
__tablename__ = 'projects'
id = Column(Integer, primary_key=True)
directory_id = Column(Integer, ForeignKey('files.id'))
class File(Base):
__tablename__ = 'files'
id = Column(Integer, primary_key=True)
path = Column(String)
parent_id = Column(Integer, ForeignKey('files.id'))
root_id = Column(Integer, ForeignKey('files.id'))
children = relationship('File', primaryjoin=id==parent_id, backref=backref('parent', remote_side=id), cascade='all')
Base.metadata.create_all(engine)
p = Project()
root = File()
root.path = ''
p.directory = root
f1 = File()
f1.path = 'test.txt'
f1.parent = root
f1.root = root
Session.add(f1)
Session.add(root)
Session.flush()
# do this otherwise f1 will be returned when calculating rf1
Session.expunge(f1)
rf1 = Session.query(File).filter(File.path == 'test.txt').one()
# this property does not exist
print rf1.root
My understanding is that defining a FK foo_id into table Foo implicit creates a foo attribute to which you can assign a Foo object.
No, it doesn't. In the snippet, it just looks like it is being done for Project.directory, but if you look at the SQL statements being echo'ed, there is no INSERT at all for the projects table.
So, for it to work, you need to add these two relationships:
class Project(Base):
...
directory = relationship('File', backref='projects')
class File(Base):
...
root = relationship('File', primaryjoin='File.id == File.root_id', remote_side=id)