Book -- draft initialization paragraphs for Chapter 13

[Dave S]

In response to the DB initialization discussion in the Users forum (see <URL:https://groups.google.com/d/msg/web2py/b-mW4VsajR4/ICT5ET26EgAJ>)

I've taken a quick swing at adding paragraphs to Chapter 13 (Deployment).  I can't do a proper pull request tonight, but I can let you peek at my scribblings so you can make comments.

I think these 2 sections should be added after Start the scheduler as a Linux service (upstart) and before Windows.

---- begin draft ----

#### Initial Queuing of a Repeating Task

Task definition is done in a model file.  But the initial

queuing of a repeating task is most easily done from a non-exposed

controller function.  By doing this in a controller

rather than in a model file, you remove unnecessary database accesses

that would occur on every request to your website.

A non-exposed function is any controller function that has an argument,

so writing something like the following in a controller (e.g. default.py)

gives you 

``

def reinit_sched(protect=None):

    # put any preparatory code here

    #

    # schedule 2 tasks:

    sched.queue_task(foo)

    sched.queue_task(bar)

    #

    # put any afters code here

``

and you can then easily call it with ``web2py.py -M -S appname/default/reinit_sched``

#### Populating a Database on Deployment

Your application may have a need for a pre-populated database table.

A simple example might be a table of color names, or the names of the

months (perhaps in a special format not used in Python datetime

routines).  More complicated examples might include an initial inventory

of parts, or the initial pages of a wiki.

The simple examples might be done via ``db.mycolors.insert()``;

the more complex examples might use a CSV file to fill in the values.

As in the task queuing section above, this should be done

using non-exposed controller functions.

Table definition for a database is done in model files, but model files

are read on every request, so one-time actions should not be in the

model files where they would lower the responsiveness of your site.

Again, a non-exposed function is any controller function that has an argument,

so writing something like the following in a controller (e.g. default.py)

gives you 

``

def populate_colors(protected=None)

    collist = ["lime","#00FF00", "olive","#808000",

                "fuchsia","#FF00FF","maroon","#800000"]:

    for i in range(0,len(collist),2):

        k,v = collist[i:i+2]

        db.mycolors.insert(name=k, code=v)

you can then easily call it with ``web2py.py -M -S appname/default/populate_colors``

For the complex example using a CSV file,

your function might look like:

def populate_parts(exposed=False):

  db.myinventory.import_from_csv_file( 

    open(os.path.join(request.folder,

                      os.path.join('private', db_parts.csv')

                     ),

         'r') 

    )

and this would be called with ``web2py.py -M -S appname/default/populate_parts``

--- end draft ---

Editors may use blue or red pencil, or large scissors.

Thanks to Niphlod, Yoel Benítez Fonseca, Richard, and Ben Lawrence 

/dps

[Niphlod]

looks good BUT I'd urge to encourage examples to include db.commit() to avoid unnecessary "I did as told but nothing worked as supposed" ^_^

[Dave S]

On Wednesday, August 31, 2016 at 3:22:15 AM UTC-7, Niphlod wrote:

looks good BUT I'd urge to encourage examples to include db.commit() to avoid unnecessary "I did as told but nothing worked as supposed" ^_^

ooops!


/dps
 

[Dave S]

Updated draft:

#### Initial Queuing of a Repeating Task

Task definition is done in a model file.  But the initial

queuing of a repeating task is most easily done from a non-exposed

controller function.  By doing this in a controller

rather than in a model file, you remove unnecessary database accesses

that would occur on every request to your website.

[The function could also be in a module or a private file,

but in the controller, the web2py API and environment is readily

accessible.]

[The function could also be in a module or a private file,

but in the controller, the web2py API and environment is readily

accessible.]

Again, a non-exposed function is any controller function that has an argument,

so writing something like the following in a controller (e.g. default.py)

gives you 

``

def populate_colors(protected=None)

    collist = ["lime","#00FF00", "olive","#808000",

                "fuchsia","#FF00FF","maroon","#800000"]:

    for i in range(0,len(collist),2):

        k,v = collist[i:i+2]

        db.mycolors.insert(name=k, code=v)

    db.commit()

you can then easily call it with ``web2py.py -M -S appname/default/populate_colors``

For the complex example using a CSV file,

your function might look like:

def populate_colors(exposed=False):

  db.mycolors.import_from_csv_file( 

    open(os.path.join(request.folder,

                      os.path.join('private', db_colors.csv')

                     ),

         'r') 

    )

  db.commit()

and this would be called with ``web2py.py -M -S appname/default/populate_colors``

See also Chapter 14,

http://web2py.com/books/default/chapter/29/14/other-recipes?search=Bayesian#Populating-database-with-dummy-data

/dps

[Dave S]

On Friday, September 2, 2016 at 3:16:53 AM UTC-7, Dave S wrote:

Updated draft:

This is PR #340 in web2py-book, but I think I got the markmin for the cross-reference wrong.

/dps