Re: [sqlalchemy] How to better understand `remote_side` in sqlalchemy?

2017-07-20 Thread Jinghui Niu 
Now I see, thanks Mike!

On Jul 20, 2017 6:51 PM, "Mike Bayer"  wrote:

> On Thu, Jul 20, 2017 at 8:10 PM, Jinghui Niu  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 
> > wrote:
> >>
> >> On Thu, Jul 20, 2017 at 1:34 PM, Jinghui Niu 
> 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,

Re: [sqlalchemy] How to better understand `remote_side` in sqlalchemy?

2017-07-20 Thread Mike Bayer 
On Thu, Jul 20, 2017 at 8:10 PM, Jinghui Niu  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 
> wrote:
>>
>> On Thu, Jul 20, 2017 at 1:34 PM, Jinghui Niu  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 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.

Re: [sqlalchemy] How to better understand `remote_side` in sqlalchemy?

2017-07-20 Thread Jinghui Niu 
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?




On Thu, Jul 20, 2017 at 4:47 PM, Mike Bayer 
wrote:

> On Thu, Jul 20, 2017 at 1:34 PM, Jinghui Niu  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.

Re: [sqlalchemy] How to better understand `remote_side` in sqlalchemy?

2017-07-20 Thread Mike Bayer 
On Thu, Jul 20, 2017 at 1:34 PM, Jinghui Niu  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 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.