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.
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>> --
>> SQLAlchemy -
>> The Python SQL Toolkit and Object Relational Mapper
>>
>> http://www.sqlalchemy.org/
>>
>> To post example code, please provide an MCVE: Minimal, Complete, and
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>
>
> --
> 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.
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--
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.
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