Now I see, thanks Mike! On Jul 20, 2017 6:51 PM, "Mike Bayer" <mike...@zzzcomputing.com> wrote:
> On Thu, Jul 20, 2017 at 8:10 PM, Jinghui Niu <niujing...@gmail.com> wrote: > > I see. But still I'm struggling to see the real difference between: > > > > Node.parent_id = Node.id > > vs. > > Node.id = Node.parent_id > > > > Aren't we just switching around sides here? > > those two conditions are equivalent. but that's not how you would > join a table to itself self-referentially. you always need at least > one of the tables to be *aliased*, so that it represents a distinct > set of rows: > > SELECT * FROM node AS n_left JOIN node AS n_right ON > n_left.parent_id = n_right.id > > can you see the difference? > > > > > > > > > > > On Thu, Jul 20, 2017 at 4:47 PM, Mike Bayer <mike...@zzzcomputing.com> > > wrote: > >> > >> On Thu, Jul 20, 2017 at 1:34 PM, Jinghui Niu <niujing...@gmail.com> > wrote: > >> > I've been studying sqlalchemy's self referential table. I've read the > >> > documentation many times and still have difficulties understanding the > >> > concept of remote_side. Could someone please draw a diagram or use an > >> > analogy to help explain this concept? I think visualizing is a better > >> > way > >> > but anything helps would be appreciated. Thanks. > >> > > >> > > >> > By the way, in my opinion the word remote is a little vague, as it can > >> > be > >> > interpreted from different angles. Like the word left and rigt, it > >> > really > >> > depends on which direction you are facing, my right could be your > left. > >> > >> > >> it's more specific than "left" and "right", because if you have: > >> > >> Node.relationship(remote_side=something) -> Node > >> > >> the "remote_side" refers specifically to the columns that are not > >> local to the Node that has the .relationship. > >> > >> That is: > >> > >> Node.col1 > >> Node.col2 > >> Node.relationship: > >> name='foo' > >> local_side=Node.col1 > >> remote_side=Node.col2 > >> > >> > >> You then know that: > >> > >> query(Node).join(Node.foo, aliased=True) > >> > >> will emit the equivalent of: > >> > >> SELECT * FROM node JOIN node AS node_remote ON node.col1 = > >> node_remote.col2 > >> > >> > >> > >> > >> > >> > >> > >> I'm > >> > not really confident in this but I would guess chaing the name from > >> > remote_side to many_side may help? Correct me if I'm wrong here. > >> > > >> > -- > >> > 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 a topic in the > >> Google Groups "sqlalchemy" group. > >> To unsubscribe from this topic, visit > >> https://groups.google.com/d/topic/sqlalchemy/e68eFOoG3LQ/unsubscribe. > >> To unsubscribe from this group and all its topics, 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 - > 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 a topic in the > Google Groups "sqlalchemy" group. > To unsubscribe from this topic, visit https://groups.google.com/d/ > topic/sqlalchemy/e68eFOoG3LQ/unsubscribe. > To unsubscribe from this group and all its topics, 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. 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