So, I've been a very happy user of SQLAlchemy over many years, though maybe not very deeply. I certainly don't really feel qualified to contribute any thoughts on it's design, but I did want to bring this up, since it's something I have run into again and again.
I'd say that in the majority of projects that involve SQLAlchemy, sooner or later I find myself in a situation where I want to work with database objects that I don't want to save to the session. It's just so damn convenient to pass them around. Here are two examples off the top of my head: - A billing tool was supposed to generate a bunch of objects (line items and so on); in preview mode, I want to use the same functions to calculate and generate the objects, and serialize them to the browser, but I don't want to save them. - In a system to check if the user has the permission to "add an object", I really wanted to construct the object temporarily, unsaved, and send it to the permission-layer, but without adding it to the session. Now often, what I do to solve this is what I think SQLAlchemy wants me to do, if I understand correctly: Configure the cascades on the relationships accordingly. But this has some problems: 1) It's *really* hard. Each time I find myself going back to the documentation, and trying to figure out where stuff needs to be changed (what does cascade_backrefs on a backref() mean again?) 2) It's error prone. It's easy to later pull in an object through some other relationship; it's also hard to later figure out exactly why the cascades where configured in the way that they are, and which code paths depend on that particular cascade setting. Changing any cascade may easily cause side effects that are not predictable. So thinking about it, changing the cascade settings on the relationship is not really what I want to do. What I really want: The cascade to work in most cases, *except this one time*. I find myself searching for a version of `session.no_autoflush`. For example: with session.no_cascade: order = Order() order.account = current_account Since current_account is in the session, the order would ordinarily be pulled into it, too. But the decorator could prevent that. Or maybe: from sqlalchemy import taint_no_cascade order = Order() taint_no_cascade(order) order.account = current_account The whole thing is probably much more complicated than that, but I desire this so frequently, I wanted to ask if it's feasable, or has been discussed before. Thanks, Michael -- 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.
