Class-DBI-Sweet
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offset
Specifies the offset of the first row to return. Defaults to 0 if
unspecified.
{ offset => 0 }
page
Specifies the current page in "page". Defaults to 1 if unspecified.
{ page => 1 }
prefetch
Specifies a listref of relationships to prefetch. These must be
has_a or might_haves or Sweet will throw an error. This will cause
Sweet to do a join across to the related tables in order to return
the related object without a second trip to the database. All
'Essential' columns of the foreign table are retrieved.
{ prefetch => [ qw/some_rel some_other_rel/ ] }
Sweet constructs the joined SQL statement by aliasing the columns in
each table and prefixing the column name with 'sweet__N_' where N is
a counter starting at 1. Note that if your database has a column
length limit (for example, Oracle's limit is 30) and you use long
column names in your application, Sweet's addition of at least 9
extra characters to your column name may cause database errors.
use_resultset_cache
Enables the resultset cache. This is a little experimental and
massive gotchas may rear their ugly head at some stage, but it does
seem to work pretty well.
For best results, the resultset cache should only be used
selectively on queries where you experience performance problems.
Enabling it for every single query in your application will most
likely cause a drop in performance as the cache overhead is greater
than simply fetching the data from the database.
profile_cache
Records cache hits/misses and what keys they were for in
->profiling_data. Note that this is class metadata so if you don't
want it to be global for Sweet you need to do
__PACKAGE__->profiling_data({ });
in either your base class or your table classes to taste.
disable_sql_paging
Disables the use of paging in SQL statements if set, forcing Sweet
to emulate paging by slicing the iterator at the end of ->search
(which it normally only uses as a fallback mechanism). Useful for
testing or for causing the entire query to be retrieved initially
when the resultset cache is used.
This is also useful when using custom SQL via "set_sql" and setting
"sql_method" (see below) where a COUNT(*) may not make sense (i.e.
when the COUNT(*) might be as expensive as just running the full
query and just slicing the iterator).
sql_method
This sets the name of the sql fragment to use as previously set by a
"set_sql" call. The default name is "Join_Retrieve" and the
associated default sql fragment set in this class is:
__PACKAGE__->set_sql( Join_Retrieve => <<'SQL' );
SELECT __ESSENTIAL(me)__%s
FROM %s
WHERE %s
SQL
You may override this in your table or base class using the same
name and CDBI::Sweet will use your custom fragment, instead.
If you need to use more than one sql fragment in a given class you
may create a new sql fragment and then specify its name using the
"sql_method" attribute.
The %s strings are replaced by sql parts as described in Ima::DBI.
See "statement_order" for the sql part that replaces each instance
of %s.
In addition, the associated statment for COUNT(*) statement has
"_Count" appended to the sql_method name. Only "from" and "where"
are passed to the sprintf function.
The default sql fragment used for "Join_Retrieve" is:
__PACKAGE__->set_sql( Join_Retrieve_Count => <<'SQL' );
SELECT COUNT(*)
FROM %s
WHERE %s
SQL
If you create a custom sql method (and set the "sql_method"
attribute) then you will likely need to also create an associated
_Count fragment. If you do not have an associated _Count, and wish
to call the "page" method, then set "disable_sql_paging" to true and
your result set from the select will be spliced to return the page
you request.
Here's an example.
Assume a CD has_a Artist (and thus Artists have_many CDs), and you
wish to return a list of artists and how many CDs each have:
In package MyDB::Artist
__PACKAGE__->columns( TEMP => 'cd_count');
__PACKAGE__->set_sql( 'count_by_cd', <<'');
SELECT __ESSENTIAL(me)__, COUNT(cds.cdid) as cd_count
FROM %s -- ("from")
WHERE %s -- ("where")
GROUP BY __ESSENTIAL(me)__
%s %s -- ("limit" and "order_by")
Then in your application code:
my ($pager, $iterator) = MyDB::Artist->page(
{
'cds.title' => { '!=', undef },
},
{
sql_method => 'count_by_cd',
statement_order => [qw/ from where limit order_by / ],
disable_sql_paging => 1,
order_by => 'cd_count desc',
rows => 10,
page => 1,
} );
The above generates the following SQL:
SELECT me.artistid, me.name, COUNT(cds.cdid) as cd_count
FROM artist me, cd cds
WHERE ( cds.title IS NOT NULL ) AND me.artistid = cds.artist
GROUP BY me.artistid, me.name
ORDER BY cd_count desc
The one caveat is that Sweet cannot figure out the has_many joins
unless you specify them in the $criteria. In the previous example
that's done by asking for all cd titles that are not null (which
should be all).
To fetch a list like above but limited to cds that were created
before the year 2000, you might do:
my ($pager, $iterator) = MyDB::Artist->page(
{
'cds.year' => { '<', 2000 },
},
{
sql_method => 'count_by_cd',
statement_order => [qw/ from where limit order_by / ],
disable_sql_paging => 1,
order_by => 'cd_count desc',
rows => 10,
page => 1,
} );
statement_order
Specifies a list reference of SQL parts that are replaced in the SQL
fragment (which is defined with "sql_method" above). The available
SQL parts are:
prefetch_cols from where order_by limit sql prefetch_names
The "sql" part is shortcut notation for these three combined:
where order_by limit
Prefecch_cols are the columns selected when a prefetch is speccified
-- use in the SELECT. Prefetch_names are just the column names for
use in GROUP BY.
This is useful when statement order needs to be changed, such as
when using a GROUP BY:
count
Returns a count of the number of rows matching the criteria. "count"
will discard "offset", "order_by", and "rows".
$count = MyApp::Article->count(%criteria);
search
Returns an iterator in scalar context, or an array of objects in list
context.
@objects = MyApp::Article->search(%criteria);
$iterator = MyApp::Article->search(%criteria);
search_like
As search but adds the attribute { cmp => 'like' }.
page
Retuns a page object and an iterator. The page object is an instance of
Data::Page.
( $page, $iterator )
= MyApp::Article->page( $criteria, { rows => 10, page => 2 );
printf( "Results %d - %d of %d Found\n",
$page->first, $page->last, $page->total_entries );
pager
An alias to page.
retrieve_all
Same as "Class::DBI" with addition that it takes "attributes" as
arguments, "attributes" can be a hash or a hashref.
$iterator = MyApp::Article->retrieve_all( order_by => 'created_on' );
retrieve_next
Returns the next record after the current one according to the order_by
attribute (or primary key if no order_by specified) matching the
criteria. Must be called as an object method.
retrieve_previous
As retrieve_next but retrieves the previous record.
CACHING OBJECTS
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