If you have cascading actions on them, you could be causing yourself a whole lot of locking headaches. Lining Bottomsīe really careful with how you set up foreign keys. ![]() My Friend Forrest® didn’t have as much luck. I’ll make you a believerĪnd we can see a delete run on all three referencing tables for both the clustered index, and the nonclustered indexes we have to support the foreign keys.īut hey, at least I got some index seeks. While query plans don’t show us locking per se, they will show us needing to go out to each table that references Users. BIG HUGS You Could Learn A Lot From A Query Plan SQL Server is all like “object locks immediately.” And, yeah, X locks on an object (table) are a lot like serializable locks on a range, just, you know, bigger. Because he’s a wonderful piece of outlier data. ![]() You could end up with really bad locking if any one or two of those things is true. Maybe there’s a begin tran or something in there for good measure (I did that to get the locking info, ha ha ha). ![]() You need to cascade down large amounts of data (this only hit about 400 rows at most).Your foreign keys aren’t indexed well (ours are, we’ll look at the query plan in a minute).You’ve got lots of cascading actions firing off (we don’t).Let’s think about a perfect storm, where… This type of lock upgrade may come as a surprise to you, but this is how SQL Server guarantees that whole referential integrity thing so that it can trust the foreign keys you’ve got on there. These locks change based on how many rows we need to get rid of.įor example, User Id 1 is hardly anything, but for the rows we need to delete, we take serializable locks – RANGEX-X. If you’ve ever watched locks for modification queries (and who doesn’t spend weekend doing that, really?), most of these will look normal to you. Is it possible to do what I'm trying to do in SQLAlchemy 2.When we run a delete for a single user, we log a Whole Mess® of locks. I'm getting the error : Mapper Mapper could not assemble any primary key columns for mapped table 'account' """Returns a default SQLAlchemy engine for sqlite if no creator is supplied."""Įngine = create_engine(f'sqlite+pysqlite:///', creator=creator) Mapper_registry.map_imperatively(Account, Account._table_cls_('account', create_engine(path: str, creator: Callable=None): Self.engine = self.create_engine(path, creator) ![]() I'm creating a "database" object for each which should take care of the mapping and such: class AccountDatabase:ĭef _init_(self, path: str, creator: Callable=None): Here, I want to for example have a database (let's call it the AccountDatabase) with only the Account table, and anotherĭatabase ( UserDatabase) that has all three tables. Interests: Mapped] = mapped_column(ListOfStrings)Īddress_id: Mapped = mapped_column(Integer, ForeignKey('address.id'), init=False)Īddress: Mapped = relationship(Address, foreign_keys=, cascade='all, delete')Īccount_id: Mapped = mapped_column(Integer, ForeignKey('account.id'), init=False, nullable=True)Īccount: Mapped = relationship(Account, foreign_keys=, cascade='all, delete') Name: Mapped = mapped_column(String)īirthdate: Mapped = mapped_column(DateTime) House_number: Mapped = mapped_column(Integer)Ĭoordinates: Mapped] = mapped_column(ListOfFloats)Īccount_id: Mapped = mapped_column(String)īalance: Mapped = mapped_column(Float) Return Table(table_name, metadata_obj, *arg, **kwargs) Id: Mapped = mapped_column(Integer, primary_key=True, autoincrement=True, init=False, _table_cls_(cls, table_name: str, metadata_obj: MetaData, *arg, **kwargs): However, I want some tables to be present in several databases. I'm trying to use SQLAlchemy for the ORM mapping, because I'm trying I have an applicaiton that manages several SQLite databases.
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