XAO Inc. > XAO-FS-1.05 > XAO::DO::FS::Glue



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Module Version: 1.35   Source   Latest Release: XAO-FS-1.06


XAO::DO::FS::Glue - glue that connects database with classes in XAO::FS


 my $odb=XAO::Objects->new(objname => 'FS::Glue',
                           dbh => $dbh);
 my $global=$odb->fetch('/');


A reference to the Glue object is what holds together all List and Hash objects in your objects database. This is the only place in API where you pass database handler.

It is quite possible that if XAO::OS would ever be implemented on top of some non-relational database layer the syntax of Glue's new() methow would change too.

In current implementation Glue also serves as a base class for both List and Hash classes and it provides some common methods. You should avoid calling them on Glue object (think of them as pure virtual methods in OO sense) and in fact you should avoid using glue object for anything but connecting to a database and retrieveing root node reference.

For XAO::Web case initialization of Glue and retrieveing of Global object is hidden from developer.

In theory Glue object should be split into ListGlue and HashGlue because now it mixes methods that know data structure inside List and Glue and this is not a Right Thing. But on the other side it is easier to keep everything that knows about SQL in just one place instead of spreading it over a couple of classes. So, do not ever rely on the fact that let's say _list_store_object is in Glue - it might move to some class of its own later.


new ($%)

Creates new Glue object and connects it to a database. There should be exactly one Glue object per process/per database.

It is highly recommended that you create a Glue object once somewhere at the top of your script, then retrieve root node object from it and keep reference for the lifetime of your script. The same applies for web scripts, especially under mod_perl - it is recommended to keep root node reference between sessions.

The only required argument is dsn (database source name). It has special format - first part is `OS', then driver name, then database name and optionally port number, hostname and so on. It is recommended to pass user name and password too. Example:

 my $odb=XAO::Objects->new(objname => 'FS::Glue',
                           dsn => 'OS:MySQL:ostest;hostname=dbserver'
                           user => 'user',
                           password => 'pAsSwOrD');

In order to get objects connected to that database you should call new on $odb with the following syntax:

 my $neworder=$odb->new(objname => 'Data::Order');
collection (%)

Creates a collection object based on parameters given. Collection is similar to List object -- it contains a list of objects having something in common. Collection is a read-only object, you can use it only to retrieve objects, not to store objects in it.

Currently the only type of collection supported is the list of all objects of the same class. This can be very useful for searching and analyzing tasks.


 my $orders=$odb->collection(class => 'Data::Order');

 my $sr=$orders->search('date_placed', ge, 12345678);

 my $sum=0;
 foreach my $id (@$sr) {
container_key ()

Works for Hash'es and List's -- returns the name of current object in upper level container.

contents ()

Alias for values() method.

destroy ()

Rough equivalent of:

 foreach my $key ($object->keys()) {
disconnect ()

If you need to explicitly disconnect from the database and you do not want to trust perl's garbage collector to do that call this method.

After you call disconnect() nearly all methods on $odb handler will throw errors and there is currently no way to re-connect existing handler to the database.

fetch ($)

Returns an object or a property referred to by the given URI. A URI must always start from / currently, relative URIs are not supported.

This method is in fact the only way to get a reference to the root object (formerly /Global):

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

Experimental extension: The following full forms can also be used:


Both should yield the same result providing that 5678 is a Collection (see XAO::DS::FS::Collection) code for P123.

glue ()

Returns reference to the Glue object the current object is received from.

objname ()

Returns relative object name that XAO::Objects would accept.

objtype ()

Always returns 'Glue' string for object database handler object.

reset ()

Useful to bring glue to a usable state after some unknown software used it. If there is an active transaction -- it will be rolled back, if there are locked tables -- they will be unlocked.

transact_active ()

Checks if a there is an active transaction at the moment. Can be used to avoid starting another one as transactions can't be nested.


  $odb->transact_begin unless $odb->transact_active;
transact_begin ()

Begins new transaction. If transactions are not supported by the underlying driver it does nothing, see transact_can() method.

If there is already an active transaction an error will be thrown and no new transaction will be started. Transactions can't be nested and each transact_begin() must be matched by a transact_commit() or transact_rollback().

Automatic transact_rollback() is performed on destroying Glue or disconnecting. It is not done automatically on thrown errors, but if an error is never caught the transaction will be rolled back automatically at the program termination stage when Glue is destroyed. Beware of global error catching blocks and do proper cleanup if you use them.


  try {
      $order->put(order_total => 123.45);
  otherwise {
      my $e=shift;
transact_can ()

Returns boolean true if underlying driver supports transactions of false otherwise.


  $odb->transact_can ||
      throw XAO::E::Sample "Transactions are not supported";
transact_commit ()

Commits changes made during the current transaction. If there is no current transaction it will throw an error assuming that there was an out-of-sync transact_commit() or transact_rollback() somewhere before.

If transactions are not supported the method will do nothing.

transact_rollback ()

Rolls back (cancels) changes made during the current transaction. If there is no current transaction it will throw an error assuming that there was an out-of-sync transact_commit() or transact_rollback() somewhere before.

If transactions are not supported the method will do nothing.

unlink ($)

Alias to delete(), which is defined in derived classes - List and Hash.

upper_class ($)

Returns the upper class name for the given class or undef for FS::Global. Will skip lists and return class name of hashes only.

Will throw an error if there is no description for the given class name.


    my $base=$odb->upper_class('Data::Order');
values ()

Returns list of values for either Hash or List.

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.

Works for both List and Hash objects. For just created object will return `undef'.


Most of the methods of Glue would be considered "protected" in more restrictive OO languages. Perl does not impose such limitations and it is up to a developer's conscience to avoid using them.

The following list is here only for reference. Names, arguments and functions performed may change from version to version. You should never use the following methods in your applications.

_class_description ()

Returns hash reference describing fields of the class name given.

_collection_setup ()

Sets up collection - base class name, key name and class_description.

_driver ()

Returns a reference to the driver for both Glue and derived objects.

_field_description ($)

Returns the description of the given field.

_field_default ($;$) {

Returns default value for the given field for a hash object. Also sets 'default' in class description if it is not there -- this might happen when old database is used with new FS.

Optional second argument is for optimization. It should hold field description hash reference if it is available in calling context.

_glue ()

Returns glue object reference. Makes sense only in derived objects! For GLue object itself would throw an error, this is expected behavior!

_hash_list_base_id ()

Returns unique_id of the hash that contains the list that contains the current hash. Used in container_object() method of Hash.

_hash_list_key_value ()

Returns what would be returned by container_key() of upper level List. Used in container_object().

_list_search (%)

Searches for elements in the list and returns a reference to the array with object IDs. See search() method in XAO::DO::FS::List for more details.

Works on Collections too.

_build_search_query (%)

Builds SQL search query according to search parameters given. See List manpage for description. Returns a reference to a hash of the following structure, not a string:

 sql          => complete SQL statement
 values       => array of values to be substituted into the SQL query
 classes      => hash with all classes and their aliases
 fields_list  => list of all fiels names
 fields_map   => hash with the map of 'condition field name' => 'sql name'
 distinct     => list of fields to be unique
 order_by     => list of fields to sort on
 post_process => is non-zero if there could be extra rows in the search
                 results because of some condition that could not be
                 expressed adequately in SQL.
 options      => original options from the FS query
_build_search_field ($$)

Builds SQL field name including table alias from field path like 'Specification/value'.

XXX - Returns array consisting of translated field name, final class name, class description and field description.

_build_search_clause ($$$$$)

Builds a list of classes used and WHERE clause for the given search conditions.

_list_setup ()

Sets up list reference fields - relation to upper hash. Makes sense only in derived objects.

check_name ($)

Checks if the given name is a valid field name to be used in put() or get(). Should not be overriden unless you fully understand potential effects.

Valid name must start from a letter and may consist from letters, digits and underscore symbol. Length is limited to 30 characters.

Returns boolean value.


MySQL chops off spaces at the end of text strings and Glue currently does not compensate for that.


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


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

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