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):

    check_name ()
        Object names in lists have nearly the same set of restrains as in
        hashes with just one exception - they can start from a digit. Such
        behavior might be extended to hashes in later versions to eliminate
        this difference.

        For example, 123ABC456 is a legal Hash id inside of a List, but is
        not a legal property ID or List ID inside of a Hash.

    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 the XAO::DO::FS::Collection manpage 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'
                                            }); 

        limit
            Indicates that you are only interested in some limited number of
            results allowing database to return just as many and therefor
            optimize the query or data transfer.

            Remember, that you can still get more results then you ask for
            if underlying database does not support this feature.

             my $subset=$persons->search('eye_color','eq','brown', {
                                             'limit' => 100
                                        });

        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: the XAO::FS manpage, the XAO::DO::FS::Hash manpage (aka
    FS::Hash), the XAO::DO::FS::Glue manpage (aka FS::Glue).

