Add example for optimistic concurrency support

5 files changed, 478 insertions, 0 deletions

diff --git a/optimistic/README b/optimistic/README
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+This example shows how to use optimistic concurrency in ODB.
+
+The example consists of the following files:
+
+person.hxx
+  Header file defining the 'person' persistent class. Besides the standard
+  persistent class pragmas, this definition also uses the 'optimistic'
+  pragma to indicate to the ODB compiler that the class must support
+  optimistic concurrency. It also uses the 'version' pragma to specify
+  which data member will contain the object version.
+
+person-odb.hxx
+person-odb.ixx
+person-odb.cxx
+person.sql
+  The first three files contain the database support code and the last file
+  contains the database schema for the person.hxx header.
+
+  These files are generated by the ODB compiler from person.hxx using the
+  following command line:
+
+  odb -d <database> --generate-schema person.hxx
+
+  Where <database> stands for the database system we are using, for example,
+  'mysql'.
+
+database.hxx
+  Contains the create_database() function which instantiates the concrete
+  database class corresponding to the database system we are using.
+
+driver.cxx
+  Driver for the example. It includes the person.hxx and person-odb.hxx
+  headers to gain access to the persistent classes and their database support
+  code. It also includes database.hxx for the create_database() function
+  declaration.
+
+  In main() the driver first calls create_database() to obtain the database
+  instance and persists a sample 'person' object. It then emulates the
+  parallel execution of two processes that try to concurrently update or
+  delete this object. For each step the driver prints the versions of the
+  object as seen by each process.
+
+To run the example we may first need to create the database schema (for some
+database systems, such as SQLite, the schema is embedded into the generated
+code which makes this step unnecessary). Using MySQL as an example, this
+can be achieved with the following command:
+
+mysql --user=odb_test --database=odb_test < person.sql
+
+Here we use 'odb_test' as the database login and also 'odb_test' as the
+database name.
+
+Once the database schema is ready, we can run the example (using MySQL as
+the database):
+
+./driver --user odb_test --database odb_test
diff --git a/optimistic/database.hxx b/optimistic/database.hxx
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+++ b/optimistic/database.hxx
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+// file      : optimistic/database.hxx
+// author    : Boris Kolpackov <boris@codesynthesis.com>
+// copyright : not copyrighted - public domain
+
+//
+// Create concrete database instance based on the DATABASE_* macros.
+//
+
+#ifndef DATABASE_HXX
+#define DATABASE_HXX
+
+#include <string>
+#include <memory>   // std::auto_ptr
+#include <cstdlib>  // std::exit
+#include <iostream>
+
+#include <odb/database.hxx>
+
+#if defined(DATABASE_MYSQL)
+#  include <odb/mysql/database.hxx>
+#elif defined(DATABASE_SQLITE)
+#  include <odb/connection.hxx>
+#  include <odb/transaction.hxx>
+#  include <odb/schema-catalog.hxx>
+#  include <odb/sqlite/database.hxx>
+#elif defined(DATABASE_PGSQL)
+#  include <odb/pgsql/database.hxx>
+#endif
+
+inline std::auto_ptr<odb::database>
+create_database (int& argc, char* argv[])
+{
+  using namespace std;
+  using namespace odb::core;
+
+  if (argc > 1 && argv[1] == string ("--help"))
+  {
+    cerr << "Usage: " << argv[0] << " [options]" << endl
+         << "Options:" << endl;
+
+#if defined(DATABASE_MYSQL)
+    odb::mysql::database::print_usage (cerr);
+#elif defined(DATABASE_SQLITE)
+    odb::sqlite::database::print_usage (cerr);
+#elif defined(DATABASE_PGSQL)
+    odb::pgsql::database::print_usage (cerr);
+#endif
+
+    exit (0);
+  }
+
+#if defined(DATABASE_MYSQL)
+  auto_ptr<database> db (new odb::mysql::database (argc, argv));
+#elif defined(DATABASE_SQLITE)
+  auto_ptr<database> db (
+    new odb::sqlite::database (
+      argc, argv, false, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE));
+
+  // Create the database schema. Due to bugs in SQLite foreign key
+  // support for DDL statements, we need to temporarily disable
+  // foreign keys.
+  //
+  {
+    connection_ptr c (db->connection ());
+
+    c->execute ("PRAGMA foreign_keys=OFF");
+
+    transaction t (c->begin ());
+    schema_catalog::create_schema (*db);
+    t.commit ();
+
+    c->execute ("PRAGMA foreign_keys=ON");
+  }
+#elif defined(DATABASE_PGSQL)
+  auto_ptr<database> db (new odb::pgsql::database (argc, argv));
+#endif
+
+  return db;
+}
+
+#endif // DATABASE_HXX
diff --git a/optimistic/driver.cxx b/optimistic/driver.cxx
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+++ b/optimistic/driver.cxx
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+// file      : optimistic/driver.cxx
+// author    : Boris Kolpackov <boris@codesynthesis.com>
+// copyright : not copyrighted - public domain
+
+#include <memory>   // std::auto_ptr
+#include <iostream>
+
+#include <odb/database.hxx>
+#include <odb/transaction.hxx>
+
+#include "database.hxx" // create_database
+
+#include "person.hxx"
+#include "person-odb.hxx"
+
+using namespace std;
+using namespace odb::core;
+
+int
+main (int argc, char* argv[])
+{
+  try
+  {
+    auto_ptr<database> db (create_database (argc, argv));
+
+    // Persist the object.
+    //
+    // At this point the initial version (1) is assigned.
+    //
+    unsigned long id;
+    {
+      person p ("John", "Doe", 21);
+
+      transaction t (db->begin ());
+      id = db->persist (p);
+      t.commit ();
+
+      cout << "version after persist: " << p.version () << endl;
+    }
+
+    // Process 1: load the object.
+    //
+    person p1;
+    {
+      transaction t (db->begin ());
+      db->load (id, p1);
+      t.commit ();
+
+      cout << "process 1 version after load: " << p1.version () << endl;
+    }
+
+    // Process 2: load the object.
+    //
+    person p2;
+    {
+      transaction t (db->begin ());
+      db->load (id, p2);
+      t.commit ();
+
+      cout << "process 2 version after load: " << p2.version () << endl;
+    }
+
+    // Process 1: update the object.
+    //
+    // At this point the version is incremented and becomes 2.
+    //
+    {
+      p1.age (20); // Correct the wrong age.
+
+      transaction t (db->begin ());
+      db->update (p1);
+      t.commit ();
+
+      cout << "process 1 version after update: " << p1.version () << endl;
+    }
+
+    // Process 2: update the object.
+    //
+    // Since the object version in this process is 1 while in the database
+    // it is 2, this operation will fail.
+    //
+    {
+      p2.age (p2.age () + 1); // Increment the age.
+
+      transaction t (db->begin ());
+
+      try
+      {
+        db->update (p2);
+      }
+      catch (const object_changed&)
+      {
+        cout << "process 2 version is out of date: " << p2.version () << endl;
+
+        // Reload the object and retry the operation. Note that the second
+        // update call cannot throw object_changed since we reloaded the
+        // object and are trying to update it in a single transaction.
+        //
+        db->reload (p2);
+
+        cout << "process 2 version after reload: " << p2.version () << endl;
+
+        p2.age (p2.age () + 1);
+        db->update (p2);
+      }
+
+      t.commit ();
+
+      cout << "process 2 version after update: " << p2.version () << endl;
+      cout << "final age value: " << p2.age () << endl;
+    }
+
+    // Process 1: delete the object if the person is younger than 21.
+    //
+    // Since the object version in this process is 2 while in the database
+    // it is 3, this operation will fail. Note that this will only hold
+    // true if we are deleting the object by passing an object instance
+    // to the erase() function. If instead we pass object id, then the
+    // object will be deleted regardless of the version.
+    //
+    if (p1.age () < 21)
+    {
+      transaction t (db->begin ());
+
+      try
+      {
+        db->erase (p1);
+        // db->erase (id); // Never throws object_changed.
+      }
+      catch (const object_changed&)
+      {
+        cout << "process 1 version is out of date: " << p1.version () << endl;
+
+        // Reload the object and retry the operation. Similar to update, the
+        // second erase call cannot throw object_changed since we reloaded
+        // the object and are trying to erase it in a single transaction.
+        //
+        db->reload (p1);
+
+        cout << "process 1 version after reload: " << p2.version () << endl;
+
+        if (p1.age () < 21)
+        {
+          db->erase (p1);
+          cout << "object deleted" << endl;
+        }
+        else
+          cout << "object not deleted" << endl;
+      }
+
+      t.commit ();
+    }
+  }
+  catch (const odb::exception& e)
+  {
+    cerr << e.what () << endl;
+    return 1;
+  }
+}
diff --git a/optimistic/makefile b/optimistic/makefile
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+++ b/optimistic/makefile
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+# file      : optimistic/makefile
+# author    : Boris Kolpackov <boris@codesynthesis.com>
+# copyright : Copyright (c) 2009-2011 Code Synthesis Tools CC
+# license   : GNU GPL v2; see accompanying LICENSE file
+
+include $(dir $(lastword $(MAKEFILE_LIST)))../build/bootstrap.make
+
+cxx_tun := driver.cxx
+odb_hdr := person.hxx
+cxx_obj := $(addprefix $(out_base)/,$(cxx_tun:.cxx=.o) $(odb_hdr:.hxx=-odb.o))
+cxx_od  := $(cxx_obj:.o=.o.d)
+
+driver  := $(out_base)/driver
+dist    := $(out_base)/.dist
+test    := $(out_base)/.test
+clean   := $(out_base)/.clean
+
+# Import.
+#
+$(call import,\
+  $(scf_root)/import/odb/stub.make,\
+  odb: odb,odb-rules: odb_rules)
+
+$(call import,\
+  $(scf_root)/import/libodb/stub.make,\
+  l: odb.l,cpp-options: odb.l.cpp-options)
+
+ifdef db_id
+$(call import,\
+  $(scf_root)/import/libodb-$(db_id)/stub.make,\
+  l: odb_db.l,cpp-options: odb_db.l.cpp-options)
+endif
+
+ifeq ($(odb_db.l.cpp-options),)
+odb_db.l.cpp-options := $(out_base)/.unbuildable
+endif
+
+# Build.
+#
+$(driver): $(cxx_obj) $(odb_db.l) $(odb.l)
+$(cxx_obj) $(cxx_od): cpp_options := -I$(out_base) -I$(src_base) -D$(db_macro)
+$(cxx_obj) $(cxx_od): $(odb.l.cpp-options) $(odb_db.l.cpp-options)
+
+genf := $(addprefix $(odb_hdr:.hxx=-odb),.hxx .ixx .cxx) $(odb_hdr:.hxx=.sql)
+gen  := $(addprefix $(out_base)/,$(genf))
+
+$(gen): $(odb)
+$(gen): odb := $(odb)
+$(gen) $(dist): export odb_options += --database $(db_id) --generate-schema \
+--table-prefix optimistic_
+$(gen): cpp_options := -I$(src_base)
+$(gen): $(odb.l.cpp-options)
+
+$(call include-dep,$(cxx_od),$(cxx_obj),$(gen))
+
+# Alias for default target.
+#
+$(out_base)/: $(driver)
+
+# Dist
+#
+name := $(subst /,-,$(subst $(src_root)/,,$(src_base)))
+
+$(dist): db_id := @database@
+$(dist): sources := $(cxx_tun)
+$(dist): headers := $(odb_hdr)
+$(dist): export name := $(name)
+$(dist): export odb_header_stem := $(basename $(odb_hdr))
+$(dist): export extra_dist := README $(call vc9projs,$(name)) \
+$(call vc10projs,$(name))
+$(dist):
+	$(call dist-data,$(sources) $(headers) README database.hxx)
+	$(call meta-automake,../template/Makefile.am)
+	$(call meta-vc9projs,../template/template,$(name))
+	$(call meta-vc10projs,../template/template,$(name))
+
+# Test.
+#
+$(test): header := $(odb_hdr)
+$(test): $(driver)
+	$(call schema)
+	$(call message,test $<,$< --options-file $(dcf_root)/db.options)
+
+# Clean.
+#
+$(clean):                            \
+  $(driver).o.clean                  \
+  $(addsuffix .cxx.clean,$(cxx_obj)) \
+  $(addsuffix .cxx.clean,$(cxx_od))  \
+  $(addprefix $(out_base)/,$(odb_hdr:.hxx=-odb.cxx.hxx.clean))
+
+# Generated .gitignore.
+#
+ifeq ($(out_base),$(src_base))
+$(driver): | $(out_base)/.gitignore
+
+$(out_base)/.gitignore: files := driver $(genf)
+$(clean): $(out_base)/.gitignore.clean
+
+$(call include,$(bld_root)/git/gitignore.make)
+endif
+
+# How to.
+#
+$(call include,$(bld_root)/dist.make)
+$(call include,$(bld_root)/meta/vc9proj.make)
+$(call include,$(bld_root)/meta/vc10proj.make)
+$(call include,$(bld_root)/meta/automake.make)
+
+$(call include,$(odb_rules))
+$(call include,$(bld_root)/cxx/cxx-d.make)
+$(call include,$(bld_root)/cxx/cxx-o.make)
+$(call include,$(bld_root)/cxx/o-e.make)
+
diff --git a/optimistic/person.hxx b/optimistic/person.hxx
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+++ b/optimistic/person.hxx
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+// file      : optimistic/person.hxx
+// author    : Boris Kolpackov <boris@codesynthesis.com>
+// copyright : not copyrighted - public domain
+
+#ifndef PERSON_HXX
+#define PERSON_HXX
+
+#include <string>
+
+#include <odb/core.hxx>
+
+#pragma db object optimistic
+class person
+{
+public:
+  person () {}
+  person (const std::string& first,
+          const std::string& last,
+          unsigned short age)
+      : first_ (first), last_ (last), age_ (age)
+  {
+  }
+
+  const std::string&
+  first () const
+  {
+    return first_;
+  }
+
+  const std::string&
+  last () const
+  {
+    return last_;
+  }
+
+  unsigned short
+  age () const
+  {
+    return age_;
+  }
+
+  void
+  age (unsigned short age)
+  {
+    age_ = age;
+  }
+
+  unsigned long
+  version () const
+  {
+    return version_;
+  }
+
+private:
+  friend class odb::access;
+
+  #pragma db id auto
+  unsigned long id_;
+
+  #pragma db version
+  unsigned long version_;
+
+  std::string first_;
+  std::string last_;
+  unsigned short age_;
+};
+
+#endif // PERSON_HXX