Christopher Fields > BioPerl-DB > Bio::DB::BioSQL::BasePersistenceAdaptor

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NAME ^

Bio::DB::BioSQL::BasePersistenceAdaptor - DESCRIPTION of Object

SYNOPSIS ^

Give standard usage here

DESCRIPTION ^

Describe the object here

FEEDBACK ^

Mailing Lists

User feedback is an integral part of the evolution of this and other Bioperl modules. Send your comments and suggestions preferably to the Bioperl mailing list. Your participation is much appreciated.

  bioperl-l@bioperl.org                  - General discussion
  http://bioperl.org/wiki/Mailing_lists  - About the mailing lists

Support

Please direct usage questions or support issues to the mailing list:

bioperl-l@bioperl.org

rather than to the module maintainer directly. Many experienced and reponsive experts will be able look at the problem and quickly address it. Please include a thorough description of the problem with code and data examples if at all possible.

Reporting Bugs

Report bugs to the Bioperl bug tracking system to help us keep track of the bugs and their resolution. Bug reports can be submitted via the web:

  http://redmine.open-bio.org/projects/bioperl/

AUTHOR - Hilmar Lapp ^

Email hlapp at gmx.net

CONTRIBUTORS ^

Additional contributors names and emails here

APPENDIX ^

The rest of the documentation details each of the object methods. Internal methods are usually preceded with a _

new

 Title   : new
 Usage   : my $obj = Bio::DB::BioSQL::BasePersistenceAdaptor->new();
 Function: Builds a new Bio::DB::BioSQL::BasePersistenceAdaptor object 
 Returns : an instance of Bio::DB::BioSQL::BasePersistenceAdaptor
 Args    :

Methods for managing persistence ^

This comprises of creating an object in the database (equivalent to an insert), storing an object in the database (equivalent to an update), removing an object from the database (equivalent to a delete), and adding and removing associations between objects when the underlying schema supports such associations.

create

 Title   : create
 Usage   : $objectstoreadp->create($obj, @params)
 Function: Creates the object as a persistent object in the datastore. This
           is equivalent to an insert.
 Example :
 Returns : A Bio::DB::PersistentObjectI implementing object wrapping the
           inserted object.
 Args    : The object to be inserted, and optionally additional (named) 
           parameters. A common parameter will
           be -fkobjs, with a reference to an array of foreign key objects
           that are not retrievable from the persistent object itself.

store

 Title   : store
 Usage   : $objectstoreadp->store($persistent_obj,@params)
 Function: Updates the given persistent object in the datastore.
 Example :
 Returns : TRUE on success and FALSE otherwise
 Args    : The object to be updated, and optionally additional (named) 
           parameters. A common parameter will
           be -fkobjs, with a reference to an array of foreign key objects
           that are not retrievable from the persistent object itself.

remove

 Title   : remove
 Usage   : $objectstoreadp->remove($persistent_obj, @params)
 Function: Removes the persistent object from the datastore.
 Example :
 Returns : TRUE on success and FALSE otherwise
 Args    : The object to be removed, and optionally additional (named) 
           parameters.

add_association

 Title   : add_assocation
 Usage   :
 Function: Stores the association between given objects in the datastore.
 Example :
 Returns : TRUE on success and FALSE otherwise
 Args    : Named parameters. At least the following must be recognized:
               -objs   a reference to an array of objects to be
                       associated with each other
               -values a reference to a hash the keys of which are
                       abstract column names and the values are values
                       of those columns.  These columns are generally
                       those other than the ones for foreign keys to
                       the entities to be associated
               -contexts optional; if given it denotes a reference
                       to an array of context keys (strings), which
                       allow the foreign key name to be determined
                       through the slot-to-column map rather than through
                       foreign_key_name().  This may be necessary if
                       more than one object of the same type takes
                       part in the association. The array must be in
                       the same order as -objs, and have the same
                       number of elements. Put undef for objects
                       for which there are no multiple contexts.
  Caveats: Make sure you *always* give the objects to be associated in the
           same order.

remove_association

 Title   : remove_assocation
 Usage   :
 Function: Removes the association between the given objects in
           the datastore.
 Example :
 Returns : TRUE on success and FALSE otherwise
 Args    : Named parameters. At least the following must be recognized:
               -objs   a reference to an array of objects the association
                       between which is to be removed
               -values a reference to a hash the keys of which are
                       abstract column names and the values are values
                       of those columns.  These columns are generally
                       those other than the ones for foreign keys to
                       the entities to be associated. Supplying this
                       is only necessary if those columns participate
                       in a unique key by which to find those
                       associations to be removed.
               -contexts optional; if given it denotes a reference
                       to an array of context keys (strings), which
                       allow the foreign key name to be determined
                       through the slot-to-column map rather than through
                       foreign_key_name().  This may be necessary if
                       more than one object of the same type takes
                       part in the association. The array must be in
                       the same order as -objs, and have the same
                       number of elements. Put undef for objects
                       for which there are no multiple contexts.
  Caveats: Make sure you *always* give the objects to be associated in the
           same order.

Making persistent objects ^

The DBAdaptorI factory mandates this operation, but it will in most cases conduct the operation by first finding the appropriate persistence adaptor and then asking the adaptor to do the operation. Hence, here is where the real stuff happens.

create_persistent

 Title   : create_persistent
 Usage   :
 Function: Takes the given object and turns it onto a
           PersistentObjectI implementing object. Returns the
           result. Does not actually create the object in a database.

           Calling this method is expected to have a recursive effect
           such that all children of the object, i.e., all slots that
           are objects themselves, are made persistent objects, too.

 Example :
 Returns : A Bio::DB::PersistentObjectI implementing object wrapping the
           passed object.
 Args    : An object to be made into a PersistentObjectI object (the class
           will be suitable for this adaptor).
           Optionally, the class which actually implements wrapping the object
           to become a PersistentObjectI.

_create_persistent

 Title   : _create_persistent
 Usage   :
 Function: Calling this method recursively replaces all eligible
           children of the object, i.e., all slots that are objects
           themselves and for which an adaptor exists, with instances
           of Bio::DB::PersistentObjectI.

           This is an internal method. Do not call from outside.
 Example :
 Returns : The first argument.
 Args    :  - A Bio::DB::PersistentObjectI implementing object, the
              class of which is suitable for this adaptor (unless on a
              recursive call).
            - Optionally, the class which actually implements wrapping
              the object to become a PersistentObjectI.

Finding objects by some property ^

This comprises of finding by primary key, finding by unique key (alternative key), finding by association, and finding by query.

find_by_primary_key

 Title   : find_by_primary_key
 Usage   : $objectstoreadp->find_by_primary_key($pk)
 Function: Locates the entry associated with the given primary key and
           initializes a persistent object with that entry.

           By default this implementation caches all objects by primary key
           if caching is enabled. Note that by default caching is disabled.
           Provide -cache_objects => 1 to the constructor in order to enable
           it.
 Example :
 Returns : An instance of the class this adaptor adapts, represented by an
           object implementing Bio::DB::PersistentObjectI, or undef if no
           matching entry was found.
 Args    : The primary key.
           Optionally, the Bio::Factory::ObjectFactoryI compliant object
           factory to be used for instantiating the proper class. If the object
           does not implement Bio::Factory::ObjectFactoryI, it is assumed to
           be the object to be populated with the query results.

find_by_unique_key

 Title   : find_by_unique_key
 Usage   :
 Function: Locates the entry matching the unique key attributes as set
           in the passed object, and populates a persistent object
           with this entry.

           This method will ask get_unique_key_query() for the actual
           alternative key(s) by which to search. It can handle
           multiple alternative keys returned by
           get_unique_key_query(). So the knowledge about which
           properties of an object constitute an alternative key, and
           how to retrieve the values for those properties, is with
           get_unique_key_query() which therefore must be overridden
           by every adaptor.

           Multiple keys will be semantically ORed with short-cut
           evaluation, meaning the method will loop over all
           alternative keys and terminate the loop as soon as a match
           is found. Thus, the order of multiple keys returned by
           get_unique_key_query() does matter.

 Example :
 Returns : A Bio::DB::PersistentObjectI implementing object, with the
           attributes populated with values provided by the entry in the
           datastore, or undef if no matching entry was found. If one was
           found, the object returned will be the first argument if that
           implemented Bio::DB::PersistentObjectI already, and a new
           persistent object otherwise.
 Args    : The object with those attributes set that constitute the chosen
           unique key (note that the class of the object must be suitable for
           the adaptor).

           Additional attributes and values if required, passed as named
           parameters. Specifically noteworthy are

            -fkobjs   a reference to an array holding foreign key
                      objects if those can't be retrieved from the
                      object itself (e.g., a Comment object will need
                      the Seq object passed with this argument)

            -obj_factory the object factory to use to create new
                      objects when a matching row is found. If not
                      specified, the passed object will be populated
                      rather than creating a new object.

            -flat_only do not retrieve and attach children (objects
                       having a foreign key to the entity handled by
                       this adaptor) if value evaluates to true
                       (default: false)

_find_by_unique_key

 Title   : _find_by_unique_key
 Usage   :
 Function: Locates the entry matching the unique key attributes as 
           set in the passed object, and populates a persistent
           object with this entry.

           This is the protected version of find_by_unique_key. Since
           it requires more upfront work to pass the right parameters
           in the right order, you should not call it from outside,
           but there may be situations where you want to call this
           method from a derived class.

 Example :
 Returns : A Bio::DB::PersistentObjectI implementing object, with the
           attributes populated with values provided by the entry in the
           datastore, or undef if no matching entry was found. If one was
           found, the object returned will be the first argument if that
           implemented Bio::DB::PersistentObjectI already, and a new
           persistent object otherwise.
 Args    : 

           - The object with those attributes set that constitute the
             chosen unique key (note that the class of the object must
             be suitable for the adaptor).

           - The query as an anonymous hash with keys being properties
             in the unique key. See get_unique_key_query() for a more
             detailed description on what the expected structure is.

           - A reference to an array of foreign key objects if
             applicable (undef if the entity doesn't have any foreign
             keys).

           - The object factory to use to create a new object if a
             matching row is found. Optional; if not specified the
             passed object will be populated with the found values
             rather than a new object created.

           - A flag indicating whether not to retrieve and attach
             children (objects having a foreign key to the object to
             build). Defaults to false if omitted, meaning children
             will be attached.

find_by_association

 Title   : find_by_association
 Usage   :
 Function: Locates those records associated between a number of objects. The
           focus object (the type to be instantiated) depends on the adaptor
           class that inherited from this class.
 Example :
 Returns : A Bio::DB::Query::QueryResultI implementing object 
 Args    : Named parameters. At least the following must be recognized:
               -objs   a reference to an array of objects to be associated with
                       each other
               -contexts optional; if given it denotes a reference
                       to an array of context keys (strings), which
                       allow the foreign key name to be determined
                       through the slot-to-column map rather than through
                       foreign_key_name().  This may be necessary if
                       more than one object of the same type takes
                       part in the association. The array must be in
                       the same order as -objs, and have the same
                       number of elements. Put undef for objects
                       for which there are no multiple contexts.
               -obj_factory the factory to use for instantiating object from
                       the found rows
               -constraints  a reference to an array of additional
                       L<Bio::DB::Query::QueryConstraint> objects
               -values  the values to bind to the constraint clauses,
                       as a hash reference keyed by the constraints
  Caveats: Make sure you *always* give the objects to be associated in the
           same order.

find_by_query

 Title   : find_by_query
 Usage   :
 Function: Locates entries that match a particular query and returns
           the result as an array of peristent objects.

           The query is represented by an instance of
           Bio::DB::Query::AbstractQuery or a derived class. Note that
           SELECT fields will be ignored and auto-determined. Give
           tables in the query as objects, class names, or adaptor
           names, and columns as slot names or foreign key class names
           in order to be maximally independent of the exact
           underlying schema. The driver of this adaptor will
           translate the query into tables and column names.

 Example :
 Returns : A Bio::DB::Query::QueryResultI implementing object
 Args    : The query as a Bio::DB::Query::AbstractQuery or derived
           instance.  Note that the SELECT fields of that query object
           will inadvertantly be overwritten.

           Optionally additional (named) parameters. Recognized
           parameters at this time are

              -fkobjs    a reference to an array of foreign key
                         objects that are not retrievable from the
                         persistent object itself

              -obj_factory  the object factory to use for creating
                         objects for resulting rows

              -name      a unique name for the query, which will make
                         the statement be a cached prepared
                         statement, which in subsequent invocations
                         will only be re-bound with parameters values,
                         but not recreated

              -values    a reference to an array holding the values
                         to be bound, if the query is a named query

              -flat_only do not retrieve and attach children (objects
                         having a foreign key to the entity handled by
                         this adaptor) if value evaluates to true
                         (default: false)

_build_object

 Title   : _build_object
 Usage   :
 Function: Build and populate an object or populate a prepuilt object from
           a row from the database.

           This is a private method primarily to centralize the code
           for this task from the various find_by_XXXX methods. Don't
           call from outside unless you know what you're doing.

 Example :
 Returns : A persistent object (implements Bio::DB::PersistentObjectI)
 Args    : Named parameters. Currently supported are:
             -obj       A prebuilt object to be populated only (optional)
             -row       a reference to an array of column values (mandatory)
             -pk        the primary key to be associated with the new object
                        (optional)
             -num_fks   the number of foreign key instances which need
                        to be associated with the object to be built
                        (optional, defaults to 0)
             -obj_factory an object factory to be used for instantiating
                        the object if it needs to be created
             -flat_only do not retrieve and attach children (objects
                        having a foreign key to the object to build)
                        if value evaluates to true (default: false)

Transaction control methods ^

This comprises of rollback and commit. The point to have those here even though they merely delegate to the driver is that the caller doesn't need to distinguish whether the RDBMS driver supports transactions or not. If the DBI driver doesn't then simply the adaptor driver won't do anything.

commit

 Title   : commit
 Usage   :
 Function: Commits the current transaction, if the underlying driver
           supports transactions.
 Example :
 Returns : TRUE
 Args    : none

rollback

 Title   : rollback
 Usage   :
 Function: Triggers a rollback of the current transaction, if the
           underlying driver supports transactions.
 Example :
 Returns : TRUE
 Args    : none

Database Context and Adaptor Driver ^

These are published attributes for convenient perusal by derived adaptors.

dbcontext

 Title   : dbcontext
 Usage   : $obj->dbcontext($newval)
 Function: Get/set the DBContextI object representing the physical database.
 Example : 
 Returns : A Bio::DB::DBContextI implementing object
 Args    : on set, the new Bio::DB::DBContextI implementing object

dbh

 Title   : dbh
 Usage   : $obj->dbh($newval)
 Function: Get/set the DBI connection handle.

           If you set this from outside, you should know exactly what
           you are doing. 

 Example : 
 Returns : value of dbh (a database handle)
 Args    : on set, the new value (a database handle, optional)

dbd

 Title   : dbd
 Usage   : $obj->dbd($newval)
 Function: Get/set the driver for this adaptor.

           The driver will usually be an instance of a class derived
           from L<Bio::DB::BioSQL::BaseDriver>. It will usually also
           have to implement L<Bio::DB::Persistent::ObjectRelMapperI>.

           If you set this from outside, you should know exactly what
           you are doing. If the value is requested in get-mode but no
           value has been set yet, the driver will be auto-loaded. Most
           if not all of the adaptors will in fact use this
           auto-loading feature.

 Example : 
 Returns : value of dbd (a scalar)
 Args    : new value (a scalar, optional)

db

 Title   : db
 Usage   : $dbadaptor = $obj->db()
 Function: This is just shorthand for $obj->dbcontext()->dbadaptor().
 Example : 
 Returns : value of db (a Bio::DB::DBAdaptorI implementing object)
 Args    : none

sth

 Title   : sth
 Usage   : $obj->sth($key, $prepared_sth)
 Function: caches prepared statements
 Example : 
 Returns : a DBI statement handle cached under the key, or all statement
           handles in the cache if no key is supplied
 Args    : the key for the cached prepared statement handle, and optionally
           on set the new statement handle to be cached, or undef to
           remove the handle from the cache

sql_generator

 Title   : sql_generator
 Usage   : $obj->sql_generator($newval)
 Function: Get/set the SQL generator object to use for turning query objects
           into SQL statements.
 Example : 
 Returns : value of sql_generator (an instance of Bio::DB::Query::SqlGenerator
           or a derived object)
 Args    : new value (an instance of Bio::DB::Query::SqlGenerator
           or a derived object, optional)

caching_mode

 Title   : caching_mode
 Usage   : $obj->caching_mode($newval)
 Function: Get/set whether objects are cached for find_by_primary_key()
           and find_by_unique_key().

           See obj_cache() for documentation on how to use the object cache.

           If you disable caching through this method, the entire
           cache will be flushed as a side effect.

 Example : 
 Returns : TRUE if caching of objects is enabled and FALSE otherwise
 Args    : new value (a scalar, optional)

obj_cache

 Title   : obj_cache
 Usage   :
 Function: Implements a simple cache of objects by key. Often, this will be
           used by derived classes to cache singletons, if there is only a
           limited number of certain base objects, like Species, or
           Ontology_Term.

           A derived adaptor may want to override this method to cache only
           selectively. The constructor of this class turns off caching by
           default; supply -cache_objects => 1 in order to turn it on, or
           call $adp->caching_mode(1).

 Example :
 Returns : The object cached under the key, or undef if there is no such key
 Args    : The key under which to cache the object.
           Optionally, on set the object to be cached. Pass undef to
           un-cache an object stored under the key.

crc64

 Title   : crc64
 Usage   :
 Function: Computes and returns the CRC64 checksum for a given string.

           This method may be called as a static method too as it
           doesn't not make any references to instance
           properties. However, it isn't really meant for outside
           consumption, but rather for derived classes as a utility
           method. At present, in fact this module itself doesn't use
           it.

           This is basically ripped out of the bioperl swissprot
           parser. Credits go to whoever contributed it there.

 Example :
 Returns : the CRC64 checksum as a string
 Args    : the string as a scalar for which to obtain the CRC64

Object Lifespan-related methods ^

finish

 Title   : finish
 Usage   : $objectadp->finish()
 Function: Finishes the resources used by this object. Note that this will
           not disconnect the database handle, but it will remove the reference
           to it.

           This behaviour is needed because the connection handle may be shared
           between multiple objects.

           Note that given the implementation here you may continue to use the
           adaptor after calling this method, since a new db handle will be
           obtained automatically if needed, and objects removed from the cache
           will be rebuilt.

           Basically, this method will reset the object cache if any and finish
           all cached statement handles and reset the statement handle cache.

           Note that this method will not throw an exception even if finishing
           the resources causes an error. It will issue a warning though, and
           if verbose() >= 1 warnings become exceptions.
 Example :
 Returns : none
 Args    : none

DESTROY

 Title   : DESTROY
 Usage   :
 Function: We override this here to call finish().
 Example :
 Returns : 
 Args    :

Abstract Methods ^

    Almost all of the following methods MUST be overridden by a
    derived class.  For some methods there is an implementation here
    that assumes "no action" is the right thing, but for many adaptors
    this won't be right. There is no way this base implementation can
    make any meaningful guesses at the correct values for those.

get_persistent_slots

 Title   : get_persistent_slots
 Usage   :
 Function: Get the slots of the object that map to attributes in its
           respective entity in the datastore.

           Slot name generally refers to a method name, but is not
           required to do so, since determining the values is under
           the control of get_persistent_slot_values().

           This is a strictly abstract method. A derived class MUST
           override it to return something meaningful.

 Example :
 Returns : an array of method names constituting the serializable slots
 Args    : the object about to be inserted or updated

get_persistent_slot_values

 Title   : get_persistent_slot_values
 Usage   :
 Function: Obtain the values for the slots returned by get_persistent_slots(),
           in exactly that order.

           The reason this method is here is that sometimes the actual
           slot values need to be post-processed to yield the value
           that gets actually stored in the database. E.g., slots
           holding arrays will need some kind of join function
           applied. Another example is if the method call needs
           additional arguments. Supposedly the adaptor for a specific
           interface knows exactly what to do here.

           Since there is also populate_from_row() the adaptor has
           full control over mapping values to a version that is
           actually stored.

           This is a strictly abstract method and it MUST be
           overridden by a derived class.

 Example :
 Returns : A reference to an array of values for the persistent slots of this
           object. Individual values may be undef.
 Args    : The object about to be serialized.
           A reference to an array of foreign key objects if not retrievable 
           from the object itself.

get_foreign_key_objects

 Title   : get_foreign_key_objects
 Usage   :
 Function: Gets the objects referenced by this object, and which therefore need
           to be referenced as foreign keys in the datastore.

           Note that the objects are expected to implement
           Bio::DB::PersistentObjectI.

           An implementation may obtain the values either through the object
           to be serialized, or through the additional arguments. An
           implementation should also make sure that the order of foreign key
           objects returned is always the same.

           Note also that in order to indicate a NULL value for a nullable
           foreign key, either put an object returning undef from 
           primary_key(), or put the name of the class instead. DO NOT SIMPLY
           LEAVE IT OUT.

           This implementation assumes a default of no foreign keys and returns
           an empty array.
 Example :
 Returns : an array of Bio::DB::PersistentObjectI implementing objects
 Args    : The object about to be inserted or updated, or undef if the call
           is for a SELECT query. In the latter case return class or interface
           names that are mapped to the foreign key tables.
           Optionally, additional named parameters. A common parameter will
           be -fkobjs, with a reference to an array of foreign key objects
           that are not retrievable from the persistent object itself.

attach_foreign_key_objects

 Title   : attach_foreign_key_objects
 Usage   :
 Function: Attaches foreign key objects to the given object as far as
           necessary.

           This method is called after find_by_XXX() queries, not for INSERTs
           or UPDATEs.

           This implementation assumes there are no foreign keys that need to
           be retrieved and instantiated. You MUST override this method
           in order to have foreign key objects taken care of upon SELECTs.
 Example :
 Returns : TRUE on success, and FALSE otherwise.
 Args    : The object to which to attach foreign key objects.
           A reference to an array of foreign key values, in the order of
           foreign keys returned by get_foreign_key_objects().

store_children

 Title   : store_children
 Usage   :
 Function: Inserts or updates the child entities of the given object in the 
           datastore.

           Usually, those child objects will reference the given object as
           a foreign key. 

           The implementation can assume that all of the child objects
           are already Bio::DB::PersistentObjectI.

           While obtaining and looping over all child objects could have been
           implemented as a generic business logic method, supplying the right
           foreign key objects is hard to accomplish in a generic fashion.

           The implementation here assumes there are no children and hence
           just returns TRUE. You MUST override it in order to have any
           children taken care of.
 Example :
 Returns : TRUE on success, and FALSE otherwise
 Args    : The Bio::DB::PersistentObjectI implementing object for which the
           child objects shall be made persistent.
           A reference to an array of foreign key values, in the order of
           foreign keys returned by get_foreign_key_objects().

attach_children

 Title   : attach_children
 Usage   :
 Function: Possibly retrieve and attach child objects of the given object.

           This is needed when whole object trees are supposed to be built
           when a base object is queried for and returned. An example would
           be Bio::SeqI objects and all the annotation objects that hang off
           of it.

           This is called by the find_by_XXXX() methods once the base object
           has been built. 

           This implementation will do nothing unless it is overridden. Whether
           to override it or not will depend on which of the children shall be
           loaded instantly instead of lazily.
 Example :
 Returns : TRUE on success, and FALSE otherwise.
 Args    : The object for which to find and to which to attach the child
           objects.

remove_children

 Title   : remove_children
 Usage   :
 Function: This method is to cascade deletes in maintained objects.

           Child records in the database will usually be cascaded by
           the RDBMS. In order to cascade removals to persistent child
           objects, you must override this method. Usually you will
           need to undefine the primary key of child objects, and
           possibly remove them from caches if they are cached.

           Because failure to do so may result in serious and often
           non-obvious bugs, there is no default provided here. You
           *must* override this method in a derived adaptor as
           evidence that you know what you are doing, even if all you
           do is just return TRUE.

 Example :
 Returns : TRUE on success and FALSE otherwise
 Args    : The persistent object that was just removed from the database.
           Additional (named) parameter, as passed to remove().

instantiate_from_row

 Title   : instantiate_from_row
 Usage   :
 Function: Instantiates the class this object is an adaptor for, and populates
           it with values from columns of the row.

           Usually a derived class will instantiate the proper class and pass
           it on to populate_from_row().

           This implementation assumes that the object factory is provided,
           uses it to instantiate a new object, and then passes on to
           populate_from_row(). If this is not appropriate the method must be
           overridden by a derived object.
 Example :
 Returns : An object, or undef, if the row contains no values
 Args    : A reference to an array of column values. The first column is the
           primary key, the other columns are expected to be in the order 
           returned by get_persistent_slots().
           Optionally, the object factory to be used for instantiating the
           proper class. The adaptor must be able to instantiate a default
           class if this value is undef.

populate_from_row

 Title   : populate_from_row
 Usage   :
 Function: Populates the given object with values from columns of the row.

           This method is strictly abstract and MUST be overridden by a
           derived object.
 Example :
 Returns : The object populated, or undef, if the row contains no values
 Args    : The object to be populated.
           A reference to an array of column values. The first column is the
           primary key, the other columns are expected to be in the order 
           returned by get_persistent_slots().

get_unique_key_query

 Title   : get_unique_key_query
 Usage   :
 Function: Obtain the suitable unique key slots and values as
           determined by the attribute values of the given object and
           the additional foreign key objects, in case foreign keys
           participate in a UK.

           This method embodies the knowledge about which properties
           constitute the alternative keys for an object (entity) and
           how to obtain the values of those properties from the
           object. Therefore, unless there is no alternative key for
           an entity, the respective (derived) adaptor must override
           this method.

           If there are multiple alternative keys for an entity, the
           overriding implementation may choose to determine at
           runtime the best alternative key given the object and then
           return only a single alternative key, or it may choose to
           return an array of (supposedly equally suitable)
           alternative keys. Note that if every alternative key
           returned will be searched for until a match is found
           (short-cut evaluation), so returning partially populated
           alternative keys is usually not wise.

           This implementation assumes there are no unique keys
           defined for the entity adapted by this class and hence
           returns an empty hash ref. Instead of overriding this
           method a derived class may choose to override
           find_by_unique_key() instead, as that one calls this
           method.

           See the documentation of find_by_unique_key() for further
           information on what the return value is used for and what
           the implications are.

 Example :
 Returns : One or more references to hash(es) where each hash
           represents one unique key, and the keys of each hash
           represent the names of the object's slots that are part of
           the particular unique key and their values are the values
           of those slots as suitable for the key.

 Args    : The object with those attributes set that constitute the chosen
           unique key (note that the class of the object will be suitable for
           the adaptor).
           A reference to an array of foreign key objects if not retrievable 
           from the object itself.
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