I'm trying to join the same table in sqlalchemy. This is a minimial version of what I tried:
#!/usr/bin/env python
import sqlalchemy as sa
from sqlalchemy import create_engine
from sqlalchemy.orm import mapper, sessionmaker, aliased
engine = create_engine('sqlite:///:memory:', echo=True)
metadata = sa.MetaData()
device_table = sa.Table("device", metadata,
sa.Column("device_id", sa.Integer, primary_key=True),
sa.Column("name", sa.String(255), nullable=False),
sa.Column("parent_device_id", sa.Integer, sa.ForeignKey('device.device_id')),
)
class Device(object):
device_id = None
def __init__(self, name, parent_device_id=None):
self.name = name
self.parent_device_id = parent_device_id
def __repr__(self):
return "<Device(%s, '%s', %s)>" % (self.device_id,
self.name,
self.parent_device_id )
mapper(Device, device_table)
metadata.create_all(engine)
db_session = sessionmaker(bind=engine)()
parent = Device('parent')
db_session.add(parent)
db_session.commit()
child = Device('child', parent.device_id)
db_session.add(child)
db_session.commit()
ParentDevice = aliased(Device, name='parent_device')
q = db_session.query(Device, ParentDevice)\
.outerjoin(ParentDevice,
Device.parent_device_id==ParentDevice.device_id)
print list(q)
This gives me this error:
ArgumentError: Can't determine join between 'device' and 'parent_device'; tables have more than one foreign key constraint relationship between them. Please specify the 'onclause' of this join explicitly.
But I am specifying a onclause for the join. How should I be doing this?
For query.[outer]join, you specify as list of joins (which is different to expression.[outer]join.) So I needed to put the 2 elements of the join, the table and the onclause in a tuple, like this:
q = db_session.query(Device, ParentDevice)\
.outerjoin(
(ParentDevice, Device.parent_device_id==ParentDevice.device_id)
)
Your mapper should specificy the connection between the two items, here's an example: adjacency list relationships.
Related
Im trying to create relations but without foreign key constraints in db
quite similar to this post:
sqlalchemy: create relations but without foreign key constraint in db?
However im trying to do it with classical mapping
and I cant figure out what Im doing wrong with it
from sqlalchemy import (
Table,
MetaData,
Column,
String,
)
from sqlalchemy.orm import mapper, relationship
from uuid import uuid4
class InspectionRecord:
def __init__(self, equipment):
self.equipment = equipment
class InspectedItem:
def __init__(self, item):
self.item = item
metadata = MetaData()
inspected_items = Table(
'inspected_items',
metadata,
Column('inspection_id', String(50)),
Column('inspected_item_id', String(50), primary_key=True),
Column('item', String(50))
)
inspection_records = Table(
'inspection_records',
metadata,
Column('inspection_id', String(50), primary_key=True, default=uuid4),
Column('equipment', String(50))
)
def start_mappers():
inspected_items_mapper = mapper(InspectedItem, inspected_items)
inspection_records_mapper = mapper(InspectionRecord, inspection_records, properties={
"inspected_items": relationship(inspected_items_mapper,
primaryjoin='foreign(inspected_items.inspection_id) == inspection_records.inspection_id',
uselist=False)}
) # this is the part where I'm having difficulties with
if __name__ == '__main__':
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
engine = create_engine('sqlite:///foo.db')
metadata.drop_all(bind=engine)
metadata.create_all(engine)
start_mappers()
Session = sessionmaker(bind=engine)
session = Session()
inspection_record = InspectionRecord(equipment='equipment_01')
session.add(inspection_record)
after so many attempts i even with additional tinkering i only get
this error
sqlalchemy.exc.InvalidRequestError: When initializing mapper mapped class InspectionRecord->inspection_records, expression '[InspectedItem.inspection_id]' failed to locate a name ("name 'InspectedItem' is not defined")
Any help would be really really really appreciated :)
got this working:
change to mapper to mapper_registry.map_imperatively
def start_mappers():
inspected_items_mapper = mapper_registry.map_imperatively(InspectedItem, inspected_items)
inspection_records_mapper = mapper_registry.map_imperatively(InspectionRecord, inspection_records, properties={
"inspected_items": relationship(InspectedItem,
primaryjoin='foreign(InspectedItem.inspection_id) == InspectionRecord.inspection_id',
uselist=False)}
I have 3 model classes from SQLAlchemy for my tables Table1 Table2 Table3
'''
from sqlalchemy import create_engine , text , select, MetaData, Table ,func , Column , String , Integer
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base
import sqlalchemy
from settings import DATABASE_URI
engine=create_engine(DATABASE_URI)
Base = declarative_base()
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
metadata = MetaData(bind=None)
session = Session()
class Table1(Base):
__tablename__ = 'table1'
id = Column(u'id', Integer(), primary_key=True)
name1 = Column(u'name1', String(50))
class Table2(Base):
__tablename__ = 'table2'
id = Column(u'id', Integer(), primary_key=True)
name2 = Column(u'name2', String(50))
class Table3(Base):
__tablename__ = 'table3'
id = Column(u'id', Integer(), primary_key=True)
name3 = Column(u'name3', String(50))
class connectionTest():
def wrapper_connection(self,table,column,value):
#SELECT column FROM table1 WHERE column = value
query = session.query(table)
q = query.filter_by(column = value)
session.execute(q)
def main():
ct = connectionTest()
t1 = Table1()
t2 = Table2()
t3 = Table3()
ct.wrapper_connection(t1,t1.name1, "Table1_Value_Information")
ct.wrapper_connection(t2,t2.name2, "Table2_Value_Information")
ct.wrapper_connection(t3,t3.name3, "Table3_Value_Information")
if __name__ == '__main__':
main()
'''
I want the wrapper connection to handle all the 3 different tables with different columns. Basically to make this as generalized as possible to handle any condition related to (#SELECT column FROM table1 WHERE column = value) Clause through SQLAlchemy ORM or Core library.
The issue I am facing is in this line.
'q = query.filter_by(column = value)'
where I am trying to pass the column information from the function attribute t1.name1
ct.wrapper_connection(t1,t1.name1, "Table1_Value_Information")
Error I am facing:
Traceback (most recent call last):
File "C:\Users<username>\AppData\Local\Programs\Python\Python37\lib\site-packages\sqlalchemy\orm\base.py", line 406, in _entity_descriptor
return getattr(entity, key)
AttributeError: type object 'Table1' has no attribute 'column'
The code in the question needs three changes:
In the wrapper_connection method, use Query.filter instead of Query.filter_by because it will accept a column object directly
Don't call Base.metadata.create_all() until after the model classes have been declared
t1 = Table1() creates a new instance of the Table1 class - a row. You want to query against the table, so use the model classes directly instead.
class connectionTest:
def wrapper_connection(self, table, column, value):
# SELECT column FROM table1 WHERE column = value
query = session.query(table)
# We have the column object, so use filter
# instead of filter_by
q = query.filter(column == value)
session.execute(q)
# Create the tables after the model classes have been declared.
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
def main():
ct = connectionTest()
# Use the model classes directly.
ct.wrapper_connection(Table1, Table1.name1, "Table1_Value_Information")
ct.wrapper_connection(Table2, Table2.name2, "Table2_Value_Information")
ct.wrapper_connection(Table3, Table3.name3, "Table3_Value_Information")
I am using SQAlchemy and python, without flask, well when I do an infinite loop and invoke the select method that sqlalchemy offers, it returns the value of my table, but when changing the value of a specific column from phpmyadmin, in the python script is not reflected the change made, someone could give me some advice or help, please thank you in advance.
PD: I leave the code for you to analyze:
from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey, create_engine, Float, DateTime, update, Date, Time
from sqlalchemy.sql import select
import time
import os
ahora = Table('ahora', metadata,
Column('id', Integer, primary_key=True),
Column('temperatura', Float()),
Column('humedad', Float()),
Column('canal1', Float()),
Column('canal2', Float()),
Column('canal3', Float()),
Column('canal4', Float()),
Column('hora', Time()),
)
engine = create_engine('mysql+pymysql://javi:javiersolis12#10.0.0.20/Tuti')
connection = engine.connect()
while True:
#Seleccionara la unica entrada en la tabla Configuracion
query = select([configuracion])
confi_actual = connection.execute(query).fetchone()
query_aux = select([ahora])
datos_actuales = connection.execute(query_aux).fetchone()
print(datos_actuales)
time.sleep(8)
You can specify the components you need to select into the Query in your Session. And then use, for example all() to get all the enterance. Please look for the next example:
import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
...
class Ahora(Base):
__tablename__ = 'ahora'
id = sa.Column(sa.Integer, primary_key=True)
temperatura: int = sa.Column(sa.Float)
...
...
engine = create_engine('mysql+pymysql://javi:javiersolis12#10.0.0.20/Tuti')
session = Session(engine)
query = session.query(Ahora)
# some actions with query, for example filter(), limit(), etc
ahora = query.all()
I am trying to obtain a row from DB, modify that row and save it again.
Everything by using SqlAlchemy
My code
from sqlalchemy import Column, DateTime, Integer, String, Table, MetaData
from sqlalchemy.orm import mapper
from sqlalchemy import create_engine, orm
metadata = MetaData()
product = Table('product', metadata,
Column('id', Integer, primary_key=True),
Column('name', String(1024), nullable=False, unique=True),
)
class Product(object):
def __init__(self, id, name):
self.id = id
self.name = name
mapper(Product, product)
db = create_engine('sqlite:////' + db_path)
sm = orm.sessionmaker(bind=db, autoflush=True, autocommit=True, expire_on_commit=True)
session = orm.scoped_session(sm)
result = session.execute("select * from product where id = :id", {'id': 1}, mapper=Product)
prod = result.fetchone() #there are many products in db so query is ok
prod.name = 'test' #<- here I got AttributeError: 'RowProxy' object has no attribute 'name'
session .add(prod)
session .flush()
Unfortunately it does not work, because I am trying to modify RowProxy object. How can I do what I want (load, change and save(update) row) in SqlAlchemy ORM way?
I assume that your intention is to use Object-Relational API.
So to update row in db you'll need to do this by loading mapped object from the table record and updating object's property.
Please see code example below.
Please note I've added example code for creating new mapped object and creating first record in table also there is commented out code at the end for deleting the record.
from sqlalchemy import Column, DateTime, Integer, String, Table, MetaData
from sqlalchemy.orm import mapper
from sqlalchemy import create_engine, orm
metadata = MetaData()
product = Table('product', metadata,
Column('id', Integer, primary_key=True),
Column('name', String(1024), nullable=False, unique=True),
)
class Product(object):
def __init__(self, id, name):
self.id = id
self.name = name
def __repr__(self):
return "%s(%r,%r)" % (self.__class__.name,self.id,self.name)
mapper(Product, product)
db = create_engine('sqlite:////temp/test123.db')
metadata.create_all(db)
sm = orm.sessionmaker(bind=db, autoflush=True, autocommit=True, expire_on_commit=True)
session = orm.scoped_session(sm)
#create new Product record:
if session.query(Product).filter(Product.id==1).count()==0:
new_prod = Product("1","Product1")
print "Creating new product: %r" % new_prod
session.add(new_prod)
session.flush()
else:
print "product with id 1 already exists: %r" % session.query(Product).filter(Product.id==1).one()
print "loading Product with id=1"
prod = session.query(Product).filter(Product.id==1).one()
print "current name: %s" % prod.name
prod.name = "new name"
print prod
prod.name = 'test'
session.add(prod)
session.flush()
print prod
#session.delete(prod)
#session.flush()
PS SQLAlchemy also provides SQL Expression API that allows to work with table records directly without creating mapped objects. In my practice we are using Object-Relation API in most of the applications, sometimes we use SQL Expressions API when we need to perform low level db operations efficiently such as inserting or updating thousands of records with one query.
Direct links to SQLAlchemy documentation:
Object Relational Tutorial
SQL Expression Language Tutorial
table:
id(integer primary key)
data(blob)
I use mysql and sqlalchemy.
To insert data I use:
o = Demo()
o.data = mydata
session.add(o)
session.commit()
I would like to insert to table like that:
INSERT INTO table(data) VALUES(COMPRESS(mydata))
How can I do this using sqlalchemy?
you can assign a SQL function to the attribute:
from sqlalchemy import func
object.data = func.compress(mydata)
session.add(object)
session.commit()
Here's an example using a more DB-agnostic lower() function:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base= declarative_base()
class A(Base):
__tablename__ = "a"
id = Column(Integer, primary_key=True)
data = Column(String)
e = create_engine('sqlite://', echo=True)
Base.metadata.create_all(e)
s = Session(e)
a1 = A()
a1.data = func.lower("SomeData")
s.add(a1)
s.commit()
assert a1.data == "somedata"
you can make it automatic with #validates:
from sqlalchemy.orm import validates
class MyClass(Base):
# ...
data = Column(BLOB)
#validates("data")
def _set_data(self, key, value):
return func.compress(value)
if you want it readable in python before the flush, you'd need to memoize it locally and use a descriptor to access it.