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authorBoris Kolpackov <boris@codesynthesis.com>2013-08-14 15:16:09 +0200
committerBoris Kolpackov <boris@codesynthesis.com>2013-08-14 15:16:09 +0200
commit22cb56f4a1ad5d2c6d581bab5e528a0cf0d13b17 (patch)
tree7d16b824f639b5133a480abb094c350eedbb1d2e /section/README
parentbb02fdbce23477d931a1572f8b2ffe52c80edf32 (diff)
Add support for object sections
Sections are an optimization mechanism that allows the partitioning of data members of a persistent class into groups that can be separately loaded and/or updated.
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+This example shows how to use object sections to implement lazy-loading
+and change-updating of a subset of data members in a persistent class.
+
+The example consists of the following files:
+
+person.hxx
+ Header file defining the 'person' persistent class. It contains a number of
+ data members some of which are made to belong to a section.
+
+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. It then persists a 'person' object, loads it back, including
+ the section, and prints the contents of its members. Finally, the driver
+ shows how to update the state of the section data members in various ways,
+ then re-loads and prints the object to verify that the changes have been
+ made persistent.
+
+To compile and link the example manually from the command line we can use
+the following commands (using MySQL as an example; replace 'c++' with your
+C++ compiler name):
+
+c++ -c person-odb.cxx
+c++ -DDATABASE_MYSQL -c driver.cxx
+c++ -o driver driver.o person-odb.o -lodb-mysql -lodb
+
+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