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JDBC ™ Technology-based Metadata Recipes

JDBC ™ Technology-based Metadata Recipes. Mahmoud Parsian Server Architect LimeLife, Inc. http://www.limelife.com. Session ID#: BOF-0367. Goal of This Talk. Learn how to use JDBC ™ metadata in homogenous and heterogeneous database environments. Agenda: JDBC ™ Metadata Recipes.

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JDBC ™ Technology-based Metadata Recipes

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  1. JDBC™Technology-based Metadata Recipes Mahmoud Parsian Server ArchitectLimeLife, Inc. http://www.limelife.com Session ID#: BOF-0367

  2. Goal of This Talk Learn how to use JDBC™metadata in homogenous and heterogeneous database environments.

  3. Agenda: JDBC™ Metadata Recipes What is metadata? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  4. Agenda: JDBC™ Metadata Recipes What is “metadata”? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  5. What is Metadata? • Metadata Definition • Metadata Examples • Database Metadata Examples • Purpose of Metadata

  6. Metadata Definition Metadata is data about data, which provide structured, descriptive information about other data. Metadata (Greek: meta-+ Latin: data “information”), literally “data about data”, is information that describes another set of data.

  7. Metadata Examples Example-1: a library catalog card, which contains data about the contents and location of a book: It is data about the data in the book referred to by the card.

  8. Metadata Examples: A Library Catalog Card A library catalog is an organized, searchable list of records that identify, describe, and locate materials in one or more library collections. Each record includes information about the material, such as its: • Author(s) • Title • Publisher • Publication Date • Subject Heading(s) • Physical Appearance (size, number of pages, maps, illustrations, etc.) • Location within a collection

  9. Database Metadata Examples Example-1: what is the list of tables and views owned by database user Alex? Example-2: what is the signature of a stored procedure called printPayroll? Example-3: what is the list of SQL keywords supported by a Connection object?

  10. Purpose of Metadata The purpose of the metadata is to make database objects in the database more accessible to users and to provide basic information about the objects in the database's collection. Each object within the database is described in a record by fields, such as: • Table/View Names • Stored Procedure names & their signatures • Connection Properties • Result Set Properties

  11. Agenda: JDBC™ Metadata Recipes What is “metadata”? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  12. What is Database Metadata? You can use database metadata to • Discover database schema and catalog information. • Discover database users, tables, views, and stored procedures. • Understand and analyze the result sets returned by SQL queries. • Find out the table, view, or column privileges. • Determine the signature of a specific stored procedure in the database. • Identify the primary(PK)/foreign(FK) keys for a given table.

  13. Agenda: JDBC™ Metadata Recipes What is metadata? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  14. What is JDBC™ Metadata? Metadata as Low-Level Objects Metadata API • DatabaseMetaData • ResultSetMetaData • ParameterMetaData • DriverPropertyInfo • RowSetMetaData Metadata Examples

  15. Metadata as Low-Level Objects

  16. Metadata API • java.sql.DatabaseMetaData • java.sql.ResultSetMetaData • java.sql.ParameterMetaData • java.sql.DriverPropertyInfo • javax.sql.RowSetMetaData

  17. Metadata Example-1Are Transactions Supported? java.sql.Connection conn = getConnection(“datasourceName”); java.sql.DatabaseMetaData meta = conn.getMetaData(); if (meta == null) { // metadata not supported by the Driver } else { // Check to see if transactions are supported if (meta.supportsTransactions()) { // Transactions are supported } else { // Transactions are not supported } }

  18. Metadata Example-2:What Are the Table Names for a Database? private static final String[] DB_TABLE_TYPES = { "TABLE" }; private static final String[] DB_VIEW_TYPES = { "VIEW" }; java.sql.Connection conn = getConnection(“datasourceName”); java.sql.DatabaseMetaData meta = conn.getMetaData(); java.sql.ResultSet tables = null; java.sql.ResultSet views = null; … views = meta.getTables(null, null, null, DB_VIEW_TYPES); tables = meta.getTables(null, null, null, DB_TABLE_TYPES); while (tables.next()) { String tableName = rs.getString(“TABLE_NAME”); }

  19. Agenda: JDBC™ Metadata Recipes What is metadata? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  20. What is a reverse engineering of a DB? Generate the original schema from database metadata: Examples: • Torque: an object-relational mapper for Java • SQL2Java:object-relational mapping tool. • Abator: a code generator for the iBATIS data mapping framework

  21. Agenda: JDBC™ Metadata Recipes What is metadata? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  22. Metadata in a Homogenous Environment Schema means the same for all DBs Catalog means the same for all DBs Connection DatabaseMetaData DriverManager MySQL Driver MySQL MySQL MySQL

  23. Agenda: JDBC™ Metadata Recipes What is metadata? What is Database metadata? What is JDBC metadata? What is a reverse engineering of a DB? Metadata in a homogenous environment Metadata in a heterogeneous environment

  24. Metadata in a Heterogeneous Environment • Metadata in a Heterogeneous Environment • Solving the Metadata Problem • Example-1: getDBNames() • Example-2: getTableNames() • DB Vendor Matters

  25. Metadata in a HeterogeneousEnvironment Schema does NOT mean the same for all DBs Catalog does NOT mean the same for all DBs Connection DatabaseMetaData DriverManager Oracle Driver PostgreSQL Driver DB2 Driver MySQL Driver MySQL Oracle PostgreSQL DB2

  26. Solving the Metadata Problem in a HeterogeneousEnvironment import java.sql.Connection; public class ConnectionObject { private Connection conn = null; private String databaseVendor = null; ConnectionObject(Connection conn, String databaseVendor) { this.conn = conn; this.databaseVendor = databaseVendor; } … get()/set() methods }

  27. Example-1: getDBNames() How do we get database names? • Oracle treats “schema” as a database name, • MySQL treats “catalog” as a database name. • In order to get the name of databases from Oracle, you must use DatabaseMetaData.getSchemas() • In order to get the name of databases from MySQL, you must use DatabaseMetaData.getCatalogs()

  28. Example-1: getDBNames() public static ResultSet getDBNames(ConnectionObject conn) throws SQLException { ResultSet dbNames = null; DatabaseMetaData meta = conn.getMetaData(); if (conn.isOracle()) { dbNames = meta.getSchemas(); } else if (conn.isMySQL()) { dbNames = meta.getCatalogs(); } else { … } return dbNames; }

  29. Example-2: getTableNames() • DatabaseMetaData.getTables() method returns the table names for a given database connection object. • The getTables() method works well for MySQL • The getTables() does NOT work well for Oracle databases (in addition to user’s tables, it returns system tables, which are not needed) • To get a list of user-defined tables and views, we use the Oracle’s metadata table called user_objects, which keeps track of objects (tables, views, ...) owned by the user. We may use the following SQL query: select object_name from user_objects where object_type = 'TABLE';

  30. Example-2: getTableNames() public static ResultSet getTableNames(ConnectionObject conn) throws SQLException { ResultSet tableNames = null; DatabaseMetaData meta = conn.getMetaData(); if (conn.isOracle()) { tableNames = getOracleTableNames(conn); // cannot use metadata } else if (conn.isMySQL()) { tableNames = meta.getTables(…); } else { … } return tableNames; }

  31. DB Vendor Matters <?xml version='1.0'> <databases> <database id="db1“, dbVendor=“mysql” <url>jdbc:mysql://localhost/octopus</url> <driver>org.gjt.mm.mysql.Driver</driver> <username>root</username><password>mysql</password> ... </database> <database id="db2“, dbVendor=“oracle” <url>jdbc:oracle:thin:@localhost:1521:kitty</url> <driver>oracle.jdbc.driver.OracleDriver</driver> <username>scott</username><password>tiger</password> ... </database> ... </databases>

  32. Summary • JDBC API enable us to get metadata • JDBC metadata can be used to develop • GUI database applications • SQL Adapters and Connectors • Reverse engineer the whole database • In using JDBC metadata, make sure to consider the “vendor” factor (this will make your DB applications to work in homogenous and heterogeneous environments)

  33. For More Information • Metadata Definition: http://en.wikipedia.org/wiki/Metadata • JDBC™ Basics: http://java.sun.com/docs/books/tutorial/jdbc/basics/ • JDBC™ API Tutorial and Reference, Third Edition By Maydene Fisher,…, Addison Wesley, 2003. • JDBC™ Metadata, MySQL and Oracle Recipes, Mahmoud Parsian, Apress.com, 2006 • Understanding JDBC™ Metadata by Kyle Brown http://members.aol.com/kgb1001001/Articles/JDBCMetadata/JDBC_Metadata.htm

  34. Q&A • Mahmoud Parsian • admin@jdbccookbook.com • mparsian@yahoo.com

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