feel free to hang here, note that some of the "chat" happens on libera.chat #sqlalchemy
@gordthompson Yes, thankfully (though not unexpectedly...as "thing1" and "x" are the same object) - their "txt" attributes have the same value. OK, so I think I understand what's going on here...and here is how I know have rewritten that 2nd sentence in my own mind:
When an incoming database row has a primary key that matches an object which is already present, the same object is returned, and those attributes of the object which already have a value will continue to return that value - even if the value returned by the row is different.
(In effect, the returned row does not overwrite the existing attribute value - should one already be set - on the object.
Have I got it right?
print(model,Cluster,type(model),type(Cluster),isinstance(model, Cluster),str(model)) yields <class 'app.models.Cluster'> <class 'app.models.Cluster'> <class 'sqlalchemy.ext.declarative.api.DeclarativeMeta'> <class 'sqlalchemy.ext.declarative.api.DeclarativeMeta'> False <class 'app.models.Cluster'> - not sure why isinstance evaluates to False as the type and string representation are the same
1 reply
sqlacodegen --generator dataclasses
Hi, I am trying to run a SQL raw query in ORM method. But the SQL Alchemy returns error and that query isn't I am expecting. Only issue with the FROM part in the query, My raw query has only one table in FROM keyword and other two tables are in JOIN where as in sqlalchemy the JOIN is okey but two tables coming with FROM keyword.
SQL Alchemy query:
result = (
session.query(ProductionMaster.article, Barcode.size, sa.func.count(Barcode.size))
.join(Barcode, Barcode.serial_no == ProductionScan.serial_no)
.join(ProductionMaster, ProductionMaster.prod_code == Barcode.prod_code)
.filter(
sa.and_(
ProductionScan.date >= "2021-08-01 08:00:00",
ProductionScan.date <= "2021-08-25 08:00:00",
ProductionMaster.article.like("%3780%black%"),
)
)
.group_by(ProductionMaster.article, Barcode.size)
.all()Error message I am getting: The multi-part identifier "tbl_ProductionScan.serial_no" could not be bound. (4104) (SQLExecDirectW)')
returned QUERY with the error message:
SELECT [Tbl_ProductionMaster].[ProductionName] AS [Tbl_ProductionMaster_ProductionName], [Tbl_barcode].[Size] AS [Tbl_barcode_Size], count([Tbl_barcode].[Size]) AS count_1
FROM [tbl_ProductionScan], [Tbl_ProductionMaster]
JOIN [Tbl_barcode] ON [Tbl_barcode].serial_no = [tbl_ProductionScan].serial_no
JOIN [Tbl_ProductionMaster] ON [Tbl_ProductionMaster].[ProductionCode] = [Tbl_barcode].[Product_Code]
WHERE [tbl_ProductionScan].prod_date >= ? AND [tbl_ProductionScan].prod_date <= ? AND [Tbl_ProductionMaster].[ProductionName] LIKE ?
GROUP BY [Tbl_ProductionMaster].[ProductionName], [Tbl_barcode].[Size]The actual query I am expecting: (This works fine)
SELECT [barcode].[dbo].[Tbl_ProductionMaster].[ProductionName]
,[barcode].[dbo].[Tbl_barcode].[Size]
,COUNT([barcode].[dbo].[Tbl_barcode].[Size])
FROM [barcode].[dbo].[tbl_ProductionScan]
INNER JOIN [barcode].[dbo].[Tbl_barcode] ON [barcode].[dbo].[Tbl_barcode].[Serial_no] = [barcode].[dbo].[tbl_ProductionScan].[serial_no]
INNER JOIN [barcode].[dbo].[Tbl_ProductionMaster] ON [barcode].[dbo].[Tbl_ProductionMaster].[ProductionCode] = [barcode].[dbo].[Tbl_barcode].[Product_code]
WHERE [barcode].[dbo].[tbl_ProductionScan].[prod_date] BETWEEN '2021-08-01 08:00:00' AND '2021-08-25 08:00:00' AND [barcode].[dbo].[Tbl_ProductionMaster].[ProductionName] Like '%3780%black%'
GROUP BY [barcode].[dbo].[Tbl_ProductionMaster].[ProductionName], [barcode].[dbo].[Tbl_barcode].[Size]
Hi everyone, i have a question about selecting only few columns from the Parent relationship,
I have this two tables:
class Parent(Base):
tablename = 'parent'
id = Column(Integer, primary_key=True)
label = Column(String)
children = relationship("Child", back_populates="parent")
class Child(Base):
tablename = 'child'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('public.parent.id'))
parent = relationship("Parent", back_populates="children")
when i use
db.query( models.Parent).first()
i get the parent object with the list of Children as i was expecting, but what i would like to do is to select only few columns like that:
db.query( models.Parent.id, models.Parent.children)
Hi all. I have a column (postgresql 14) that I thought would update on every row update (1.4.27), declared as follows:
class utcnow(expression.FunctionElement): # pylint: disable=W0223
type = DateTime()
...
updated_at = Column(
DateTime(True),
nullable=False,
onupdate=utcnow(),
server_default=utcnow(),
index=True,
)This was what I came up with. I had the impression it works... sometimes. What am I missing?
Hello,
I have a problem but I'm not sure whether it belongs here or with sqlalchemy. Once that determined I'll provide the required details.
Using sqlalchemy's PickleType I'm loading large files BLOBs into Oracle. Unfortunatelly they are too large and I get DPI-1057: buffer size too large.
From oracle/python-cx_Oracle#480 I learned that streaming writes must be used in order to write LOBs larger than 1073741822B.
As far as I know cx-Oracle provides DB-API implementation that's used by sqlalchemy, but I'm uncertain on exactly where is the boundary.
This brings me to my question:
Does support for streaming writes (to support large LOBs) is something to be implemented in python-cx-Oracle or in sqlalchemy?
@CaselIT
I think I'm stuck because of not understanding the difference between different abstractions:
- cx-Oracle
- DBAPI
- sqlalchemy dialects
- sqlalchemy core
My current understanding is that cx-Oracle is Python wrapper to Oracle Client libraries. It exposes a DBAPI (PEP249) compatibile interface
I'm unclear about "Oracle dialect" - https://docs.sqlalchemy.org/en/14/dialects/.
Is that a separate thing that sits between core and the DBAPI driver? Or it's part of either cx-Oracle or SQLAlchemy Core?
That sounds like a reasonable approach. We're using SQLAlchemy across the whole application, so it'd be nice to be able to interface is somehow.
Would it go something like this?
connection = engine.raw_connection()
cursor = connection.cursor()https://stackoverflow.com/a/49816320/12640922
And then that's the same cursor & connection they are using here:
id_val = 9
lob_var = cursor.var(cx_Oracle.DB_TYPE_BLOB)
cursor.execute("""
insert into lob_tbl (id, b)
values (:1, empty_blob())
returning b into :2""", [id_val, lob_var])
blob, = lobVar.getvalue()
offset = 1
num_bytes_in_chunk = 65536
with open("image.png", "rb") as f:
while True:
data = f.read(num_bytes_in_chunk)
if data:
blob.write(data, offset)
if len(data) < num_bytes_in_chunk:
break
offset += len(data)
connection.commit()https://cx-oracle.readthedocs.io/en/latest/user_guide/lob_data.html#streaming-lobs-write
class Box(BaseModel):
__tablename__ = "box"
id = Column(Integer, primary_key=True)
category = Column(String)
class Folder(BaseModel):
__tablename__ = "folder"
id = Column(Integer, primary_key=True)
box_id = Column(Integer, ForeignKey('box.id'))
box = relationship(Box, backref=backref("folders"))
category = ??? # In particular, I don't want this column to ACTUALLY exist in this table
# I'd like:
session.query(Folder).filter(Folder.category == "Mid-17th-Century Pocket Lint Collectors")
# to implicitly result in SQL with the effect of:
SELECT * FROM folder, box WHERE folder.box_id = box.id and box.category = 'Mid-17th-Century Pocket Lint Collectors'category = column_property(box.category) should work, but apparently the box field isn't populated yet at that point, because I get an AttributeError on box.category.
@CaselIT: So using association proxy with my earlier example, like
class Folder(BaseModel):
...
box_id = Column(Integer, ForeignKey('box.id'))
box = relationship(Box, backref=backref("folders"))
category = association_proxy("box", "category")Though referencing it works in some contexts (like .filter(Folder.category == "x"), it doesn't transparently work in other field contexts. Specifically:
session.query(Folder.category).all()
-> InvalidRequestError: SQL expression, column, or mapped entity expected - got 'ColumnAssociationProxyInstance(AssociationProxy('box', 'category'))'Any way to make that work? What I want is for callers not to have to know that this isn't a real column.