Jifty::DBI::Collection(3p)

NAME
Jifty::DBI::Collection - Encapsulate SQL queries and rows in simple perl objects

SYNOPSIS
  use Jifty::DBI::Collection;

  package My::Things;
  use base qw/Jifty::DBI::Collection/;

  package main;

  use Jifty::DBI::Handle;
  my $handle = Jifty::DBI::Handle->new();
  $handle->connect( Driver => 'SQLite', Database => "my_test_db" );

  my $sb = My::Things->new( handle => $handle );

  $sb->limit( column => "column_1", value => "matchstring" );

  while ( my $record = $sb->next ) {
      print $record->my_column_name();
  }

DESCRIPTION
This module provides an object-oriented mechanism for retrieving and updating data in a DBI-accessible database.

In order to use this module, you should create a subclass of Jifty::DBI::Collection and a subclass of Jifty::DBI::Record for each table that you wish to access. (See the documentation of Jifty::DBI::Record for more information on subclassing it.)

Your Jifty::DBI::Collection subclass must override "new_item", and probably should override at least "_init" also; at the very least, "_init" should probably call "_handle" and "_table" to set the database handle (a Jifty::DBI::Handle object) and table name for the class -- see the "SYNOPSIS" for an example.

METHODS

  new
Creates a new Jifty::DBI::Collection object and immediately calls "_init" with the same parameters that were passed to "new". If you haven't overridden _init in your subclass, this means that you should pass in a Jifty::DBI::Handle (or one of its subclasses) like this:

   my $sb = My::Jifty::DBI::Subclass->new( handle => $handle );

However, if your subclass overrides "_init" you do not need to take a handle argument, as long as your subclass takes care of calling the "_handle" method somehow. This is useful if you want all of your Jifty::DBI objects to use a shared global handle and don't want to have to explicitly pass it in each time, for example.

  _init
This method is called by new with whatever arguments were passed to "new". By default, it takes a "Jifty::DBI::Handle" object as a "handle" argument and calls "_handle" with that.

  clean_slate
This completely erases all the data in the object. It's useful if a subclass is doing funky stuff to keep track of a search and wants to reset the object's data without losing its own data; it's probably cleaner to accomplish that in a different way, though.

  implicit_clauses
Called by "clean_slate" to set up any implicit clauses that the collection always has. Defaults to doing nothing. Is passed the paramhash passed into "new".

  _handle [DBH]
Get or set this object's Jifty::DBI::Handle object.

  _do_search
This internal private method actually executes the search on the database; it is called automatically the first time that you actually need results (such as a call to "next").

  add_record RECORD
Adds a record object to this collection.

This method automatically sets our "must redo search" flag to 0 and our "we have limits" flag to 1.

Without those two flags, counting the number of items wouldn't work.

  _record_count
This private internal method returns the number of Jifty::DBI::Record objects saved as a result of the last query.

  _do_count
This internal private method actually executes a counting operation on the database; it is used by "count" and "count_all".

  _apply_limits STATEMENTREF
This routine takes a reference to a scalar containing an SQL statement. It massages the statement to limit the returned rows to only "$self->rows_per_page" rows, skipping "$self->first_row" rows. (That is, if rows are numbered starting from 0, row number "$self->first_row" will be the first row returned.) Note that it probably makes no sense to set these variables unless you are also enforcing an ordering on the rows (with "order_by_cols", say).

  _distinct_query STATEMENTREF
This routine takes a reference to a scalar containing an SQL statement. It massages the statement to ensure a distinct result set is returned.

  _build_joins
Build up all of the joins we need to perform this query.

  _is_joined
Returns true if this collection will be joining multiple tables together.

  _is_limited
If we've limited down this search, return true. Otherwise, return false.

  build_select_query
Builds a query string for a "SELECT rows from Tables" statement for this collection

  preload_columns
The columns that the query would load for result items. By default it's everything.

XXX TODO: in the case of distinct, it needs to work as well.

  class_and_column_for_alias
Takes the alias you've assigned to a prefetched related object. Returns the class of the column we've declared that alias preloads.

  prefetch ALIAS_NAME ATTRIBUTE
prefetches all related rows from alias ALIAS_NAME into the record attribute ATTRIBUTE of the sort of item this collection is.

If you have employees who have many phone numbers, this method will let you search for all your employees
    and prepopulate their phone numbers.

Right now, in order to make this work, you need to do an explicit join between your primary table and the subsidiary tables AND then specify the name of the attribute you want to prefetch related data into. This method could be a LOT smarter. since we already know what the relationships between our tables are, that could all be precomputed.

XXX TODO: in the future, this API should be extended to let you specify columns.

  distinct_required
Returns true if Jifty::DBI expects that this result set will end up with repeated rows and should be "condensed" down to a single row for each unique primary key.

Out of the box, this method returns true if you've joined to another table. To add additional logic, feel free to override this method in your subclass.

XXX TODO: it should be possible to create a better heuristic than the simple "is it joined?" question we're asking now. Something along the lines of "are we joining this table to something that is not the other table's primary key"

  build_select_count_query
Builds a SELECT statement to find the number of rows this collection
 would find.

  do_search
"Jifty::DBI::Collection" usually does searches "lazily". That is, it does a "SELECT COUNT" or a "SELECT" on the fly the first time you ask for results that would need one or the other. Sometimes, you need to display a count of results found before you iterate over a collection, but you know you're about to do that too. To save a bit of wear and tear on your database, call "do_search" before that "count".

  next
Returns the next row from the set as an object of the type defined by sub new_item. When the complete set has been iterated through, returns undef and resets the search such that the following call to "next" will start over with the first item retrieved from the database.

  goto_first_item
Starts the recordset counter over from the first item. The next time you call "next", you'll get the first item returned by the database, as if you'd just started iterating through the result set.

  goto_item
Takes an integer, n. Sets the record counter to n. the next time you call "next", you'll get the nth item.

  first
Returns the first item

  last
Returns the last item

  items_array_ref
Return a reference to an array containing all objects found by this search.

  new_item
Should return a new object of the correct type for the current collection. Must be overridden by a subclassed.

  record_class
Returns the record class which this is a collection of; override this to subclass. Or, pass it the name of a class an an argument after creating a "Jifty::DBI::Collection" object to create an 'anonymous' collection class.

If you haven't specified a record class, this returns a best guess at the name of the record class for this collection.

It uses a simple heuristic to determine the record class name -- It chops "Collection" off its own name. If you want to name your records and collections differently, go right ahead, but don't say we didn't warn you.

  redo_search
Takes no arguments. Tells Jifty::DBI::Collection that the next time it's asked for a record, it should requery the database

  unlimit
Clears all restrictions and causes this object to return all rows in the primary table.

  limit
Takes a hash of parameters with the following keys:

table
    Can be set to something different than this table if a join is wanted (that means we can't do recursive joins as for now).

alias
    Unless alias is set, the join criterias will be taken from EXT_LINKcolumn and INT_LINKcolumn and added to the criterias. If alias is set, new criterias about the foreign table will be added.

column
    Column to be checked against.

value
    Should always be set and will always be quoted. If the value is a subclass of Jifty::DBI::Object, the value will be interpreted to be the object's id.

operator
    operator is the SQL operator to use for this phrase. Possible choices include:

    "="
    "!="
        Any other standard SQL comparision operators that your underlying database supports are also valid.

    "LIKE"
    "NOT LIKE"
    "MATCHES"
        MATCHES is like LIKE, except it surrounds the value with % signs.

    "STARTSWITH"
        STARTSWITH is like LIKE, except it only appends a % at the end of the string

    "ENDSWITH"
        ENDSWITH is like LIKE, except it prepends a % to the beginning of the string

entry_aggregator
    Can be AND or OR (or anything else valid to aggregate two clauses in SQL)

case_sensitive
    on some databases, such as postgres, setting case_sensitive to 1 will make this search case sensitive. Note that this flag is ignored if the column is numeric.

  open_paren CLAUSE
Places an open paren at the current location in the given "CLAUSE". Note that this can be used for Deep Magic, and has a high likelyhood of allowing you to construct malformed SQL queries. Its interface will probably change in the near future, but its presence allows for arbitrarily complex queries.

  close_paren CLAUSE
Places a close paren at the current location in the given "CLAUSE". Note that this can be used for Deep Magic, and has a high likelyhood of allowing you to construct malformed SQL queries. Its interface will probably change in the near future, but its presence allows for arbitrarily complex queries.

  order_by_cols DEPRECATED
*DEPRECATED*. Use "order_by" method.

  order_by EMPTY|HASH|ARRAY_OF_HASHES
Orders the returned results by column(s) and/or function(s) on column(s).

Takes a paramhash of "alias", "column" and "order" or "function" and "order". "alias" defaults to main. "order" defaults to ASC(ending), DES(cending) is also a valid value. "column" and "function" have no default values.

Use "function" instead of "alias" and "column" to order by the function value. Note that if you want use a column as argument of the function then you have to build correct reference with alias in the "alias.column" format.

Use array of hashes to order by many columns/functions.

The results would be unordered if method called without arguments.

Returns the current list of columns.

  _order_clause
returns the ORDER BY clause for the search.

  group_by_cols DEPRECATED
*DEPRECATED*. Use group_by method.

  group_by EMPTY|HASH|ARRAY_OF_HASHES
Groups the search results by column(s) and/or function(s) on column(s).

Takes a paramhash of "alias" and "column" or "function". "alias" defaults to main. "column" and "function" have no default values.

Use "function" instead of "alias" and "column" to group by the function value. Note that if you want use a column as argument of the function then you have to build correct reference with alias in the "alias.column" format.

Use array of hashes to group by many columns/functions.

The method is EXPERIMENTAL and subject to change.

  _group_clause
Private function to return the "GROUP BY" clause for this query.

  new_alias table_OR_CLASS
Takes the name of a table or a Jifty::DBI::Record subclass. Returns the string of a new Alias for that table, which can be used to Join tables or to limit what gets found by a search.

  join
Join instructs Jifty::DBI::Collection to join two tables.

The standard form takes a param hash with keys "alias1", "column1", "alias2" and "column2". "alias1" and "alias2" are column aliases obtained from $self->new_alias or a $self->limit. "column1" and "column2" are the columns in "alias1" and "alias2" that should be linked, respectively. For this type of join, this method has no return value.

Supplying the parameter "type" => 'left' causes Join to perform a left join. in this case, it takes "alias1", "column1", "table2" and "column2". Because of the way that left joins work, this method needs a table for the second column rather than merely an alias. For this type of join, it will return the alias generated by the join.

The parameter "operator" defaults "=", but you can specify other operators to join with.

Instead of "alias1"/"column1", it's possible to specify expression, to join "alias2"/"table2" on an arbitrary expression.

  set_page_info [per_page => NUMBER,] [current_page => NUMBER]
Sets the current page (one-based) and number of items per page on the pager object, and pulls the number of elements from the collection. This both sets up the collection's Data::Page object so that you can use its calculations, and sets the Jifty::DBI::Collection "first_row" and "rows_per_page" so that queries return values from the selected page.

  rows_per_page
limits the number of rows returned by the database. Optionally, takes an integer which restricts the # of rows returned in a result Returns the number of rows the database should display.

  first_row
Get or set the first row of the result set the database should return. Takes an optional single integer argrument. Returns the currently set integer first row that the database should return.

  _items_counter
Returns the current position in the record set.

  count
Returns the number of records in the set.

  count_all
Returns the total number of potential records in the set, ignoring any limit_clause.

  is_last
Returns true if the current row is the last record in the set.

  DEBUG
Gets/sets the DEBUG flag.

  column
Normally a collection object contains record objects populated with all columns in the database, but you can restrict the records to only contain some particular columns, by calling the "column" method once for each column you are interested in.

Takes a hash of parameters; the "column", "table" and "alias" keys means the same as in the "limit" method. A special "function" key may contain one of several possible kinds of expressions:

"DISTINCT COUNT"
    Same as "COUNT(DISTINCT ?)".

Expression with "?" in it
    The "?" is substituted with the column name, then passed verbatim to the underlying "SELECT" statement.

Expression with "(" in it
    The expression is passed verbatim to the underlying "SELECT".

Any other expression
    The expression is taken to be a function name. For example, "SUM" means the same thing as SUM(?).

  columns LIST
Specify that we want to load only the columns in LIST, which is a

  columns_in_db table
Return a list of columns in table, lowercased.

TODO: Why are they lowercased?

  has_column { table => undef, column => undef }
Returns true if table has column column. Return false otherwise

  table [table]
If called with an argument, sets this collection's table.

Always returns this collection's table.

  clone
Returns copy of the current object with all search restrictions.

  _cloned_attributes
Returns list of the object's fields that should be copied.

If your subclass store references in the object that should be copied while clonning then you probably want override this method and add own values to the list.

TESTING
In order to test most of the features of "Jifty::DBI::Collection", you need to provide "make test" with a test database. For each DBI driver that you would like to test, set the environment variables "JDBI_TEST_FOO", "JDBI_TEST_FOO_USER", and "JDBI_TEST_FOO_PASS" to a database name, database username, and database password, where "FOO" is the driver name in all uppercase. You can test as many drivers as you like. (The appropriate "DBD::" module needs to be installed in order for the test to work.) Note that the "SQLite" driver will automatically be tested if "DBD::Sqlite" is installed, using a temporary file as the database. For example:

  JDBI_TEST_MYSQL=test JDBI_TEST_MYSQL_USER=root JDBI_TEST_MYSQL_PASS=foo \
    JDBI_TEST_PG=test JDBI_TEST_PG_USER=postgres  make test

AUTHOR
Copyright (c) 2001-2005 Jesse Vincent, jesse@fsck.com.

All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO
Jifty::DBI::Handle, Jifty::DBI::Record.