NAME

       UR::Context::Transaction - API for software transactions

SYNOPSIS

         my $o = Some::Obj->create(foo => 1);
         print "o's foo is ",$o->foo,"\n";  # prints 1

         my $t = UR::Context::Transaction->begin();

         $o->foo(4);

         print "In transaction, o's foo is ",$o->foo,"\n";  # prints 4

         if (&should_we_commit()) {
             $t->commit();
             print "Transaction committed, o's foo is ",$o->foo,"\n";  # prints 4

         } else {
             $t->rollback();
             print "Transaction rollback, o's foo is ",$o->foo,"\n";  # prints 1
         }

DESCRIPTION

       UR::Context::Transaction instances represent in-memory transactions as a diff of the
       contents of the object cache in the Process context.  Transactions are nestable.  Their
       instances exist in the object cache and  are subject to the same scoping rules as other
       UR-based objects, meaning that they do not disappear mearly because the lexical variable
       they're assigned to goes out of scope.  They must be explicitly disposed of via the commit
       or rollback methods.

INHERITANCE

       UR::Context::Transaction is a subclass of UR::Context

CONSTRUCTOR

       begin
             $t = UR::Context::Transaction->begin();

           Creates a new software transaction context to track changes to UR-based objects.  As
           all activity to objects occurs in some kind of transaction context, the newly created
           transaction exists within whatever context was current before the call to begin().

             $t = UR::Context::Transaction->begin(commit_validator => sub { ... });

           A validation function may be assigned with the "commit_validator" property.  When the
           transaction is committed, this function is called.  The commit proceeds if this
           function returns a true value.  The default function, "changes_can_be_saved" requires
           that all objects changed within the transaction be valid, ie. that
           "$obj-"__errors__()> returns an empty list.  The validation function is passed one
           argument: the transaction object being committed.

METHODS

       commit
             $t->commit();

           Causes all objects with changes to save those changes back to the underlying context.

           If the validation function (specified with the "commit_validator" param when the
           transaction was created with "begin()") returns false, the changes are not committed
           to the encompassing context, "commit()" returns false and this transaction remains in
           effect.

           Returns true if all the transaction's changes are committed to the encompassing
           Context.  This transaction object then becomes invalid, and its state will be
           'committed'.

       rollback
             $t->rollback();

           Causes all objects with changes to have those changes reverted to their state when the
           transaction began.  Classes with properties whose meta-property is_transactional => 0
           are not tracked within a transaction and will not be reverted.

           After "rollback()", this transaction becomes invalid, and the object will become a
           UR::DeletedRef.

       delete
             $t->delete();

           delete() is a synomym for rollback

       has_changes
             $bool = $t->has_changes();

           Returns true if any UR-based objects have changes within the transaction.

       get_changes
             @changes = $t->get_changes();

           Return a list or UR::Change objects representing changes within the transaction.

CLASS METHODS

       eval
             UR::Context::Transaction::eval BLOCK

           Executes the BLOCK (with no arguments) wrapped by a software transaction and a
           CORE::eval.  If the BLOCK dies then the exception is caught and the software
           transaction is rolled back.

       do
             UR::Context::Transaction::do BLOCK

           Executes the BLOCK (with no arguments) wrapped by a software transaction and a
           CORE::eval.  If the BLOCK returns a true value and does not die then the software
           transaction is committed.  If the BLOCK returns false or dies then the software
           transaction is rolled back.

           If the BLOCK throws an exception, it will be caught, the software transaction rolled
           back, and the exception will be re-thrown with die().

EXPORTS

       This module can export constants that match the valid values of the "state" property:
       TRANSACTION_STATE_OPEN and TRANSACTION_STATE_COMMITTED

SEE ALSO

       UR::Context