NAME

XAO::DO::FS::List - List class for XAO::FS

SYNOPSIS

my $customers_list=$odb->fetch('/Customers');

my $customer=$customers_list->get('cust0001');

DESCRIPTION

List object usually used as is without overwriting it. The XAO class name for the list object is FS::List.

A list object provides methods for managing a list of FS::Hash objects of the same class -- storing, retrieving and searching on them.

List class shares most of the API with the Hash class.

Here is the list of all List methods (alphabetically):

container_key ()

Returns key that refers to the current List in the upper level Hash.

container_object ()

Returns a reference to the hash that contains current list.

Example:

my $customer=$orders_list->container_object();

Do not abuse this method, it involves a lot of overhead and can slow your application down if abused.

delete ($)

Deletes object from the list - first call destroy on the object to recursively delete its content and then drops it from the list.

detach ()

Detaches current object from the database. Not implemented, but safe to use in read-only situations.

exists ($)

Checks if an object with the given name exists in the list and returns boolean value.

get (@)

Retrieves a Hash object from the List using the given name.

As a convenience you can pass more then one object name to the get() method to retrieve multiple Hash references at once.

If an object does not exist an error will be thrown.

get_new ()

Convenience method that returns new empty detached object of the type, that list can store.

keys ()

Returns unsorted list of all keys for all objects stored in that list.

new (%)

You cannot use this method directly. Use some equivalent of the following code to get List reference:

$hash->add_placeholder(name => 'Orders',
                       type => 'list',
                       class => 'Data::Order',
                       key => 'order_id');

my $orders_list=$hash->get('Orders');

objtype ()

For all List objects always return a string 'List'.

put ($;$)

The only difference between list object's put() and data object's put() is that key argument is not required. Unique key would be generated and returned from the method if only one argument is given.

Key is guaranteed to consist of up to 20 alphanumeric characters. Key would uniquely identify stored object in the current list scope, it does not have to be unique among all objects of that class.

Value have to be a reference to an object of the same class as was defined when that list object was created.

Example of adding new object into list:

my $customer=XAO::Objects->new(objname => 'Data::Customer');
my $id=$custlist->put($customer);

Attempt to put already attached data object into an attached list under the same key name is meaningless and would do nothing.

Note: An object stored by calling put() method is not modified and remains in detached state if it was detached. If an object already existed in the list under the same ID - its content would be totally replaced by new object's content. It is safe to call put() to store attached object under new name - the object would be cloned. In order to retrieve new stored object from database you will have to call get().

search (@)

Returns a reference to the list of IDs of objects corresponding to the given criteria.

Takes a perl array or perl array reference of the following format:

[ [ 'first_name', 'ws', 'a'], 'or', [ 'age', 'gt', 20 ] ]

All innermost conditions consist of exactly three elements -- first is an object property name, second is a comparison operator and third is some arbitrary value to compare field with or array reference.

As a convenience if right hand side value refers to an array in condition then the meaning of that block is to compare given field using given operator with all listed values and join results using OR logical operator. These two examples are completely equal and would be translated to the same database query:

my $r=$list->search('name', 'wq', [ 'big', 'ugly' ]);

my $r=$list->search([ 'name', 'wq', 'big' ], 
                    'or',
                    [ 'name', 'wq', 'ugly' ]);

It is possible to search on properties of some objects inner to the objects in the list. Let's say you have a list with specification values inside of a product. To search for products having specific value in their specification you would then do:

my $r=$list->search(['Specification/name', 'eq', 'Width'],
                    'and',
                    ['Specification/value', 'eq', '123']);

This can be extended as deep as you want. See also collection() method on Glue and XAO::DO::FS::Collection for additional search capabilities.

Multiple blocks may be combined into complex expressions using logical operators.

Comparison operators:

cs

True if the field contains given string. There are no limitations as to what could be in the string. Having dictionary on the field will not speed up search.

eq

True if equal.

ge

True if greater or equal.

gt

True if greater.

le

True if less or equal.

lt

True if less.

ne

True if not equal.

wq

True if property contains the given word completely. For example ['name', 'wq', 'ann'] would math 'Ann Peters' and 'Marie Ann', but would not match 'Annette'.

For best performance please make this kind of search only on fields of type 'words' -- in that case the search is performed by dictionary and is very fast.

ws

True if property contains a word that starts with the given text. For example ['name', 'ws', 'an'] would match 'Andrew' and 'Marie Ann', but 'Joann' would not match.

Works best on fields of type 'words'.

Logical operators:

and - true if both are true (has an alias -- '&&')

or - true if either one is true (has an alias -- '||')

Examples:

##
# Search for persons in the given age bracket
#
my $list=$persons->search([ 'age', 'ge', 25 ],
                          'and',
                          [ 'age', 'le', 35 ]);

##
# A little more complex search.
#
my $list=$persons->search([ 'name', 'ws', 'john' ],
                          'and',
                          [ [ 'balance', 'ge', 10000 ],
                            'or',
                            [ 'rating', 'ge', 2.5 ]
                          ]);

The search() method can also accept additional options that can alter sorting or uniqueness of search results. These options are listed after required three first elements. Supported options are:

orderby

To sort results using any field in either ascending or descending order. Example:

my $list=$persons->search('age', 'gt', 60, {
                              'orderby' => [
                                  ascend => 'first_name',
                                  descend => 'second_name',
                              ]
                         });

Note, that you pass an array reference, not a hash reference to preserve the order of arguments.

If you want to order using just one field it is safe to pass that field name without wrapping it into array reference (sorting will be performed in ascending order then):

my $list=$persons->search('age', 'gt', 60, {
                              'orderby' => 'first_name'
                         });

Caveats: There is no way to alter sorting tables that would be used by the database. It is generally safe to assume that english letters and digits would be sorted in the expected way. But there is no guarantee of that.

Remember that even though you sort results on the content of a field it is not that field that would be returned to you, you will still get a list of object IDs.

distinct

To only get the rows that have unique values in the given field. Example:

my $color_ids=$products->search('category_id', 'eq', 123, {
                                   'distinct' => 'color'
                               }); 

Beware that these options usually significantly decrease search performance. Only use them when you would do sorting or select unique rows in your code anyway.

As a degraded case of search it is safe to pass nothing or just options to select everything in the given list. Examples:

##
# These two lines are roughly equivalent. Note that you get an array
# reference in the first line and an array itself in the second.
#
my $keys=$products->search();

my @keys=$products->keys();

##
# This is the way to get all the keys ordered by price.
#
my $keys=$products->search({ orderby => 'price' });

values ()

Returns a list of all Hash objects in the list.

Note: the order of values is the same as the order of keys returned by keys() method. At least until you modify the object directly on indirectly. It is not recommended to use values() method for the reason of pure predictability.

uri ($)

Returns complete URI to either the object itself (if no argument is given) or to a property with the given name.

That URI can then be used to retrieve a property or object using $odb->fetch($uri). Be aware, that fetch() is relatively slow method and should not be abused.

Example:

my $uri=$customer->uri;
print "URI of that customer is: $uri\n";

AUTHORS

Xao, Inc. (c) 2001. This module was developed by Andrew Maltsev <am@xao.com> with the help and valuable comments from other team members.

SEE ALSO

Further reading: XAO::FS, XAO::DO::FS::Hash (aka FS::Hash), XAO::DO::FS::Glue (aka FS::Glue).