Обсуждение: How to intelligently work with views that depend on other views

I have a bunch of views, and some views use data from other views.

For example, view A might get used by view B and view B gets used by view C.

Several times now, as I got further into the project, I've changed how
I make some views and I've had to redefine not just that view, but all
the ones that depend on it.

This is getting frustrating!  When I want to change how I make view A,
I have to drop view A cascade, and then view B and view C are dropped.

Then I have to remember to re-create B and C after I rewrite A.

There's likely a better solution...

What is it?

GO POSTGRESQL!


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W. Matthew Wilson
matt@tplus1.com
http://tplus1.com


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Melvin Davidson wrote:

The best solution, IMHO, is don't create views that depend on other
views. ...

Much better to just make each view a stand alone.

Seconding Mr. Davidson's advice.

But, given that you are in the situation, here is a workable alternative:


Matthew Wilson

On Thu, Aug 6, 2015 at 4:44 PM, W. Matthew Wilson <matt@tplus1.com
<mailto:matt@tplus1.com>> wrote:

    I have a bunch of views, and some views use data from other views.

...
    Several times now, as I got further into the project, I've changed how
    I make some views and I've had to redefine not just that view, but all
    the ones that depend on it.

1. Dump the data base:


  pg_dump mydatabase -U postgres -Fc > mydatabase.dump


2. Create a list of all data base objects from the dump file


  pg_restore -l mydatabase.dump > mydatabase.list


3. Edit the list file and delete all rows except those for your views A, B, and C. Make sure you leave the lines corresponding to those views in the order in which they appear in the list file, as the following step will then have commands in the right dependency order.


4. Generate a SQL command file, based on the dump and the edited list file:


   pg_restore -C -L mydatabase.list mydatabase.dump > sql


5. Edit your view definitions in the SQL command file.


6. Run the SQL command file:


  psql mydatabase -U postgres -f sql

As Mr. Wilson suggested, you can use pg_dump to extract the views, but I also suggest downloading and installing pg_extractor, which uses pg_dump but allows more options to dump just the objects you need. IE: views, functions, etc.

Here's the url to download.
https://github.com/omniti-labs/pg_extractor

These url's give more detail about it.

http://www.keithf4.com/pg_extractor/

https://www.youtube.com/watch?v=a7P4TV8xUOM

On Thu, Aug 6, 2015 at 7:41 PM, Berend Tober <btober@computer.org> wrote:

Melvin Davidson wrote:

The best solution, IMHO, is don't create views that depend on other
views. ...

Much better to just make each view a stand alone.

Seconding Mr. Davidson's advice.

But, given that you are in the situation, here is a workable alternative:


Matthew Wilson

On Thu, Aug 6, 2015 at 4:44 PM, W. Matthew Wilson <matt@tplus1.com
<mailto:matt@tplus1.com>> wrote:

    I have a bunch of views, and some views use data from other views.

...
    Several times now, as I got further into the project, I've changed how
    I make some views and I've had to redefine not just that view, but all
    the ones that depend on it.

1. Dump the data base:


  pg_dump mydatabase -U postgres -Fc > mydatabase.dump


2. Create a list of all data base objects from the dump file


  pg_restore -l mydatabase.dump > mydatabase.list


3. Edit the list file and delete all rows except those for your views A, B, and C. Make sure you leave the lines corresponding to those views in the order in which they appear in the list file, as the following step will then have commands in the right dependency order.


4. Generate a SQL command file, based on the dump and the edited list file:


   pg_restore -C -L mydatabase.list mydatabase.dump > sql


5. Edit your view definitions in the SQL command file.


6. Run the SQL command file:


  psql mydatabase -U postgres -f sql

--

Melvin Davidson
I reserve the right to fantasize.  Whether or not you
wish to share my fantasy is entirely up to you.