Re: [sqlalchemy] How to handle unique constraint for multiple columns containing null values using sqlachemy?
I should add, please specify which backend you're using and what DDL sequence you are looking to emit. On Tue, Nov 6, 2018 at 3:21 PM Mike Bayer wrote: > > On Tue, Nov 6, 2018 at 2:54 PM wrote: > > > > Hi, > > > > I find that `UniqueConstraint` from `sqlachemy` and > > `op.create_unique_constraint` by `alembic`, it cannot handle multiple > > columns that contain null values. > > > > I saw we can solve using SQL commands via some tricky ways like creating > > unique index and coalesce, do we have some ways using `sqlachemy` instead > > of directly using `SQL` to solve this issue? > > > the UniqueConstraint object spits out "CREATE UNIQUE CONSTRAINT" or > equivalent DDL only. The "null values" issue is very different > across backends - in particular, the limitation that NULL values > aren't allowed is a peculiarity specific to Microsoft SQL Server. > > Given that, there are ways to create DDL that does what you need, and > then if necessary, to have different kinds of DDL emit based on > different backends if you are looking for cross-database > compatibility. For intricate edge cases like this, it's much better > that SQLAlchemy gives the developer the tools to create exactly the > DDL sequence that is tailored towards their needs, rather than it > trying to pre-package a particular solution that probably won't work > the same way across different backends or otherwise be flexible > enough. > > > > > > Thanks! > > > > Lydia > > > > -- > > SQLAlchemy - > > The Python SQL Toolkit and Object Relational Mapper > > > > http://www.sqlalchemy.org/ > > > > To post example code, please provide an MCVE: Minimal, Complete, and > > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > > description. > > --- > > You received this message because you are subscribed to the Google Groups > > "sqlalchemy" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to sqlalchemy+unsubscr...@googlegroups.com. > > To post to this group, send email to sqlalchemy@googlegroups.com. > > Visit this group at https://groups.google.com/group/sqlalchemy. > > For more options, visit https://groups.google.com/d/optout. -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
Re: [sqlalchemy] How to handle unique constraint for multiple columns containing null values using sqlachemy?
On Tue, Nov 6, 2018 at 2:54 PM wrote: > > Hi, > > I find that `UniqueConstraint` from `sqlachemy` and > `op.create_unique_constraint` by `alembic`, it cannot handle multiple columns > that contain null values. > > I saw we can solve using SQL commands via some tricky ways like creating > unique index and coalesce, do we have some ways using `sqlachemy` instead of > directly using `SQL` to solve this issue? the UniqueConstraint object spits out "CREATE UNIQUE CONSTRAINT" or equivalent DDL only. The "null values" issue is very different across backends - in particular, the limitation that NULL values aren't allowed is a peculiarity specific to Microsoft SQL Server. Given that, there are ways to create DDL that does what you need, and then if necessary, to have different kinds of DDL emit based on different backends if you are looking for cross-database compatibility. For intricate edge cases like this, it's much better that SQLAlchemy gives the developer the tools to create exactly the DDL sequence that is tailored towards their needs, rather than it trying to pre-package a particular solution that probably won't work the same way across different backends or otherwise be flexible enough. > > Thanks! > > Lydia > > -- > SQLAlchemy - > The Python SQL Toolkit and Object Relational Mapper > > http://www.sqlalchemy.org/ > > To post example code, please provide an MCVE: Minimal, Complete, and > Verifiable Example. See http://stackoverflow.com/help/mcve for a full > description. > --- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy+unsubscr...@googlegroups.com. > To post to this group, send email to sqlalchemy@googlegroups.com. > Visit this group at https://groups.google.com/group/sqlalchemy. > For more options, visit https://groups.google.com/d/optout. -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
[sqlalchemy] How to handle unique constraint for multiple columns containing null values using sqlachemy?
Hi, I find that `UniqueConstraint` from `sqlachemy` and `op.create_unique_constraint` by `alembic`, it cannot handle multiple columns that contain null values. I saw we can solve using SQL commands via some tricky ways like creating unique index and coalesce, do we have some ways using `sqlachemy` instead of directly using `SQL` to solve this issue? Thanks! Lydia -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at https://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
