Trail: JDBC(TM) Database Access
Lesson: JDBC Basics
Using Structured Objects
Home Page > JDBC(TM) Database Access > JDBC Basics

Using Structured Objects

Note: MySQL and Java DB currently do not support user-defined types. Consequently, no JDBC tutorial example is available to demonstrate the features described in this section.

The following topics are covered:

Overview of Structured Types

SQL structured types and DISTINCT types are the two data types that a user can define in SQL. They are often referred to as UDTs (user-defined types), and you create them with a SQL CREATE TYPE statement.

Getting back to the example of The Coffee Break, suppose that the owner has been successful beyond all expectations and has been expanding with new branches. The owner has decided to add a STORES table to the database containing information about each establishment. STORES will have four columns:

The owner makes the column LOCATION be a SQL structured type, the column COF_TYPES a SQL ARRAY, and the column MGR a REF(MANAGER), with MANAGER being a SQL structured type.

The first thing the owner must define the new structured types for the address and the manager. A SQL structured type is similar to structured types in the Java programming language in that it has members, called attributes, that may be any data type. The owner writes the following SQL statement to create the new data type ADDRESS:

CREATE TYPE ADDRESS
(
    NUM INTEGER,
    STREET VARCHAR(40),
    CITY VARCHAR(40),
    STATE CHAR(2),
    ZIP CHAR(5)
);

In this statement, the new type ADDRESS has five attributes, which are analogous to fields in a Java class. The attribute NUM is an INTEGER, the attribute STREET is a VARCHAR(40), the attribute CITY is a VARCHAR(40), the attribute STATE is a CHAR(2), and the attribute ZIP is a CHAR(5).

The following excerpt, in which con is a valid Connection object, sends the definition of ADDRESS to the database:

String createAddress =
    "CREATE TYPE ADDRESS " +
    "(NUM INTEGER, STREET VARCHAR(40), " +
    "CITY VARCHAR(40), STATE CHAR(2), ZIP CHAR(5))";
Statement stmt = con.createStatement();
stmt.executeUpdate(createAddress);

Now the ADDRESS structured type is registered with the database as a data type, and the owner can use it as the data type for a table column or an attribute of a structured type.

Using DISTINCT Type in Structured Type

One of the attributes the owner of The Coffee Break plans to include in the new structured type MANAGER is the manager's telephone number. Because the owner will always list the telephone number as a 10-digit number (to be sure it includes the area code) and will never manipulate it as a number, the owner decides to define a new type called PHONE_NO that consists of 10 characters. The SQL definition of this data type, which can be thought of as a structured type with only one attribute, looks like this:

CREATE TYPE PHONE_NO AS CHAR(10);

Or, as noted earlier, for some drivers the definition might look like this:

CREATE DISTINCT TYPE PHONE_NO AS CHAR(10);

A DISTINCT type is always based on another data type, which must be a predefined type. In other words, a DISTINCT type cannot be based on a user-defined type (UDT). To retrieve or set a value that is a DISTINCT type, use the appropriate method for the underlying type (the type on which it is based). For example, to retrieve an instance of PHONE_NO, which is based on a CHAR type, you would use the method getString because that is the method for retrieving a CHAR.

Assuming that a value of type PHONE_NO is in the fourth column of the current row of the ResultSet object rs, the following line of code retrieves it:

String phoneNumber = rs.getString(4);

Similarly, the following line of code sets an input parameter that has type PHONE_NO for a prepared statement being sent to the database:

pstmt.setString(1, phoneNumber);

Adding on to the previous code fragment, the definition of PHONE_NO will be sent to the database with the following line of code:

stmt.executeUpdate(
    "CREATE TYPE PHONE_NO AS CHAR(10)");

After registering the type PHONE_NO with the database, the owner can use it as a column type in a table or as the data type for an attribute in a structured type. The definition of MANAGER in the following SQL statement uses PHONE_NO as the data type for the attribute PHONE:

CREATE TYPE MANAGER
(
    MGR_ID INTEGER,
    LAST_NAME VARCHAR(40),
    FIRST_NAME VARCHAR(40),
    PHONE PHONE_NO
);

Reusing stmt, defined previously, the following code fragment sends the definition of the structured type MANAGER to the database:

  String createManager =
    "CREATE TYPE MANAGER " +
    "(MGR_ID INTEGER, LAST_NAME " +
    "VARCHAR(40), " +
    "FIRST_NAME VARCHAR(40), " +
    "PHONE PHONE_NO)";
  stmt.executeUpdate(createManager);

Using References to Structured Types

The owner of The Coffee Break has created three new data types used as column types or attribute types in the database: The structured types LOCATION and MANAGER, and the DISTINCT type PHONE_NO. The entrepreneur has used PHONE_NO as the type for the attribute PHONE in the new type MANAGER, and ADDRESS as the data type for the column LOCATION in the table STORES. The MANAGER type could be used as the type for the column MGR, but instead the entrepreneur prefers to use the type REF(MANAGER) because the entrepreneur often has one person manage two or three stores. Using REF(MANAGER) as a column type avoids repeating all the data for MANAGER when one person manages more than one store.

With the structured type MANAGER already created, the owner can now create a table containing instances of MANAGER that can be referenced. A reference to an instance of MANAGER will have the type REF(MANAGER). A SQL REF is nothing more than a logical pointer to a structured type, so an instance of REF(MANAGER) serves as a logical pointer to an instance of MANAGER.

Because a SQL REF value needs to be permanently associated with the instance of the structured type that it references, it is stored in a special table together with its associated instance. A programmer does not create REF types directly but rather creates the table that will store instances of a particular structured type that can be referenced. Every structured type that is to be referenced will have its own table. When you insert an instance of the structured type into the table, the database automatically creates a REF instance. For example, to contain instances of MANAGER that can be referenced, the owner created the following special table using SQL:

  CREATE TABLE MANAGERS OF MANAGER
  (OID REF(MANAGER)
  VALUES ARE SYSTEM GENERATED);

This statement creates a table with the special column OID, which stores values of type REF(MANAGER). Each time an instance of MANAGER is inserted into the table, the database will generate an instance of REF(MANAGER) and store it in the column OID. Implicitly, an additional column stores each attribute of MANAGER that has been inserted into the table, as well. For example, the following code fragment shows how the entrepreneur created three instances of the MANAGER structured type to represent three managers:

  INSERT INTO MANAGERS (
    MGR_ID, LAST_NAME,
    FIRST_NAME, PHONE) VALUES
  (
    000001,
    'MONTOYA',
    'ALFREDO',
    '8317225600'
  );

  INSERT INTO MANAGERS (
    MGR_ID, LAST_NAME,
    FIRST_NAME, PHONE) VALUES
  (
    000002,
    'HASKINS',
    'MARGARET',
    '4084355600'
  );

  INSERT INTO MANAGERS (
    MGR_ID, LAST_NAME,
    FIRST_NAME, PHONE) VALUES
  (
    000003,
    'CHEN',
    'HELEN',
    '4153785600'
   );

The table MANAGERS will now have three rows, one row for each manager inserted so far. The column OID will contain three unique object identifiers of type REF(MANAGER), one for each instance of MANAGER. These object identifiers were generated automatically by the database and will be permanently stored in the table MANAGERS. Implicitly, an additional column stores each attribute of MANAGER. For example, in the table MANAGERS, one row contains a REF(MANAGER) that references Alfredo Montoya, another row contains a REF(MANAGER) that references Margaret Haskins, and a third row contains a REF(MANAGER) that references Helen Chen.

To access a REF(MANAGER) instance, you select it from its table. For example, the owner retrieved the reference to Alfredo Montoya, whose ID number is 000001, with the following code fragment:

  String selectMgr =
    "SELECT OID FROM MANAGERS " +
    "WHERE MGR_ID = 000001";
  ResultSet rs = stmt.executeQuery(selectMgr);
  rs.next();
  Ref manager = rs.getRef("OID");

Now the variable manager can be used as a column value that references Alfredo Montoya.

Sample Code for Creating SQL REF Object

The following code example creates the table MANAGERS, a table of instances of the structured type MANAGER that can be referenced, and inserts three instances of MANAGER into the table. The column OID in this table will store instances of REF(MANAGER). After this code is executed, the MANAGERS table will have a row for each of the three MANAGER objects inserted, and the value in the OID column will be the REF(MANAGER) type that identifies the instance of MANAGER stored in that row.

package com.oracle.tutorial.jdbc;

import java.sql.*;

public class CreateRef {

    public static void main(String args[]) {

        JDBCTutorialUtilities myJDBCTutorialUtilities;
        Connection myConnection = null;

        if (args[0] == null) {
            System.err.println("Properties file not specified " +
                               "at command line");
            return;
        } else {
            try {
                myJDBCTutorialUtilities = new JDBCTutorialUtilities(args[0]);
            } catch (Exception e) {
                System.err.println("Problem reading properties " +
                                   "file " + args[0]);
                e.printStackTrace();
                return;
            }
        }

        Connection con = null;
        Statement stmt = null;

        try {
            String createManagers =
                "CREATE TABLE " +
                "MANAGERS OF MANAGER " +
                "(OID REF(MANAGER) " +
                "VALUES ARE SYSTEM " +
                "GENERATED)";

            String insertManager1 =
                "INSERT INTO MANAGERS " +
                "(MGR_ID, LAST_NAME, " +
                "FIRST_NAME, PHONE) " +
                "VALUES " +
                "(000001, 'MONTOYA', " +
                "'ALFREDO', " +
                "'8317225600')";

            String insertManager2 =
                "INSERT INTO MANAGERS " +
                "(MGR_ID, LAST_NAME, " +
                "FIRST_NAME, PHONE) " +
                "VALUES " +
                "(000002, 'HASKINS', " +
                "'MARGARET', " +
                "'4084355600')";

            String insertManager3 =
                "INSERT INTO MANAGERS " +
                "(MGR_ID, LAST_NAME, " +
                "FIRST_NAME, PHONE) " +
                "VALUES " +
                "(000003, 'CHEN', 'HELEN', " +
                "'4153785600')";
  
            con = myJDBCTutorialUtilities.getConnection();
            con.setAutoCommit(false);

            stmt = con.createStatement();
            stmt.executeUpdate(createManagers);

            stmt.addBatch(insertManager1);
            stmt.addBatch(insertManager2);
            stmt.addBatch(insertManager3);
            int [] updateCounts = stmt.executeBatch();

            con.commit();

            System.out.println("Update count for:  ");
            for (int i = 0; i < updateCounts.length; i++) {
                System.out.print("    command " + (i + 1) + " = ");
                System.out.println(updateCounts[i]);
            }
        } catch(BatchUpdateException b) {
            System.err.println("-----BatchUpdateException-----");
            System.err.println("Message:  " + b.getMessage());
            System.err.println("SQLState:  " + b.getSQLState());
            System.err.println("Vendor:  " + b.getErrorCode());
            System.err.print("Update counts for " + "successful commands:  ");
            int [] rowsUpdated = b.getUpdateCounts();
            for (int i = 0; i < rowsUpdated.length; i++) {
                System.err.print(rowsUpdated[i] + "   ");
            }
            System.err.println("");
        } catch(SQLException ex) {
            System.err.println("------SQLException------");
            System.err.println("Error message:  " + ex.getMessage());
            System.err.println("SQLState:  " + ex.getSQLState());
            System.err.println("Vendor:  " + ex.getErrorCode());
        } finally {
            if (stmt != null) { stmt.close(); }
              JDBCTutorialUtilities.closeConnection(con);
        }
    }
}

Using User-Defined Types as Column Values

Our entrepreneur now has the UDTs required to create the table STORES. The structured type ADDRESS is the type for the column LOCATION, and the type REF(MANAGER) is the type for the column MGR.

The UDT COF_TYPES is based on the SQL data type ARRAY and is the type for the column COF_TYPES. The following line of code creates the type COF_ARRAY as an ARRAY value with 10 elements. The base type of COF_ARRAY is VARCHAR(40).

  CREATE TYPE COF_ARRAY AS ARRAY(10) OF VARCHAR(40);

With the new data types defined, the following SQL statement creates the table STORES:

  CREATE TABLE STORES
  (
    STORE_NO INTEGER,
    LOCATION ADDRESS,
    COF_TYPES COF_ARRAY,
    MGR REF(MANAGER)
  );

Inserting User-Defined Types into Tables

The following code fragment inserts one row into the STORES table, supplying values for the columns STORE_NO, LOCATION, COF_TYPES, and MGR, in that order:

  INSERT INTO STORES VALUES
  (
    100001,
    ADDRESS(888, 'Main_Street',
      'Rancho_Alegre',
      'CA', '94049'),
    COF_ARRAY('Colombian', 'French_Roast',
      'Espresso', 'Colombian_Decaf',
      'French_Roast_Decaf'),
    SELECT OID FROM MANAGERS
      WHERE MGR_ID = 000001
  );

The following goes through each column and the value inserted into it.

  STORE_NO: 100001

This column is type INTEGER, and the number 100001 is an INTEGER type, similar to entries made before in the tables COFFEES and SUPPLIERS.

  LOCATION: ADDRESS(888, 'Main_Street',
    'Rancho_Alegre', 'CA', '94049')

The type for this column is the structured type ADDRESS, and this value is the constructor for an instance of ADDRESS. When we sent the definition of ADDRESS was sent to the database, one of the things it did was to create a constructor for the new type. The comma-separated values in parentheses are the initialization values for the attributes of the ADDRESS type, and they must appear in the same order in which the attributes were listed in the definition of the ADDRESS type. 888 is the value for the attribute NUM, which is an INTEGER value. "Main_Street" is the value for STREET, and "Rancho_Alegre" is the value for CITY, with both attributes being of type VARCHAR(40). The value for the attribute STATE is "CA", which is of type CHAR(2), and the value for the attribute ZIP is "94049", which is of type CHAR(5).

  COF_TYPES: COF_ARRAY(
    'Colombian',
    'French_Roast',
    'Espresso',
    'Colombian_Decaf',
    'French_Roast_Decaf'),

The column COF_TYPES is of type COF_ARRAY with a base type of VARCHAR(40), and the comma-separated values between parentheses are the String objects that are the array elements. The owner defined the type COF_ARRAY as having a maximum of 10 elements. This array has 5 elements because the entrepreneur supplied only 5 String objects for it.

  MGR: SELECT OID FROM MANAGERS
    WHERE MGR_ID = 000001

The column MGR is type REF(MANAGER), which means that a value in this column must be a reference to the structured type MANAGER. All of the instances of MANAGER are stored in the table MANAGERS. All of the instances of REF(MANAGER) are also stored in this table, in the column OID. The manager for the store described in this table row is Alfredo Montoya, and his information is stored in the instance of MANAGER that has 100001 for the attribute MGR_ID. To get the REF(MANAGER) instance associated with the MANAGER object for Alfredo Montoya, select the column OID that is in the row where MGR_ID is 100001 in the table MANAGERS. The value that will be stored in the MGR column of the STORES table (the REF(MANAGER) value) is the value the DBMS generated to uniquely identify this instance of the MANAGER structured type.

Send the preceding SQL statement to the database with the following code fragment:

  String insertMgr =
    "INSERT INTO STORES VALUES " +
    "(100001, " +
    "ADDRESS(888, 'Main_Street', " +
      "'Rancho_Alegre', 'CA', " +
      "'94049'), " +
    "COF_ARRAY('Colombian', " +
      "'French_Roast', 'Espresso', " +
      "'Colombian_Decaf', " +
      "'French_Roast_Decaf'}, " +
    "SELECT OID FROM MANAGERS " +
    "WHERE MGR_ID = 000001)";

  stmt.executeUpdate(insertMgr);

However, because you are going to send several INSERT INTO statements, it will be more efficient to send them all together as a batch update, as in the following code example:

package com.oracle.tutorial.jdbc;

import java.sql.*;

public class InsertStores {
    public static void main(String args[]) {

        JDBCTutorialUtilities myJDBCTutorialUtilities;
        Connection myConnection = null;

        if (args[0] == null) {
            System.err.println(
                "Properties file " +
                "not specified " +
                "at command line");
            return;
        } else {
            try {
                myJDBCTutorialUtilities = new
                    JDBCTutorialUtilities(args[0]);
            } catch (Exception e) {
                System.err.println(
                    "Problem reading " +
                    "properties file " +
                    args[0]);
                e.printStackTrace();
                return;
            }
        }

        Connection con = null;
        Statement stmt = null;

        try {
            con = myJDBCTutorialUtilities.getConnection();
            con.setAutoCommit(false);

            stmt = con.createStatement();

            String insertStore1 =
                "INSERT INTO STORES VALUES (" +
                "100001, " +
                "ADDRESS(888, 'Main_Street', " +
                    "'Rancho_Alegre', 'CA', " +
                    "'94049'), " +
                "COF_ARRAY('Colombian', " +
                    "'French_Roast', " +
                    "'Espresso', " +
                    "'Colombian_Decaf', " +
                    "'French_Roast_Decaf'), " +
                "(SELECT OID FROM MANAGERS " +
                "WHERE MGR_ID = 000001))";

            stmt.addBatch(insertStore1);

            String insertStore2 =
                "INSERT INTO STORES VALUES (" +
                "100002, " +
                "ADDRESS(1560, 'Alder', " +
                    "'Ochos_Pinos', " +
                    "'CA', '94049'), " +
                "COF_ARRAY('Colombian', " +
                    "'French_Roast', " +
                    "'Espresso', " +
                    "'Colombian_Decaf', " +
                    "'French_Roast_Decaf', " +
                    "'Kona', 'Kona_Decaf'), " +
                "(SELECT OID FROM MANAGERS " +
                "WHERE MGR_ID = 000001))";

            stmt.addBatch(insertStore2);

            String insertStore3 =
                "INSERT INTO STORES VALUES (" +
                "100003, " +
                "ADDRESS(4344, " +
                    "'First_Street', " +
                    "'Verona', " +
                    "'CA', '94545'), " +
                "COF_ARRAY('Colombian', " +
                    "'French_Roast', " +
                    "'Espresso', " +
                    "'Colombian_Decaf', " +
                    "'French_Roast_Decaf', " +
                    "'Kona', 'Kona_Decaf'), " +
                "(SELECT OID FROM MANAGERS " +
                "WHERE MGR_ID = 000002))";

            stmt.addBatch(insertStore3);

            String insertStore4 =
                "INSERT INTO STORES VALUES (" +
                "100004, " +
                "ADDRESS(321, 'Sandy_Way', " +
                    "'La_Playa', " +
                    "'CA', '94544'), " +
                "COF_ARRAY('Colombian', " +
                    "'French_Roast', " +
                    "'Espresso', " +
                    "'Colombian_Decaf', " +
                    "'French_Roast_Decaf', " +
                    "'Kona', 'Kona_Decaf'), " +
                "(SELECT OID FROM MANAGERS " +
                "WHERE MGR_ID = 000002))";

            stmt.addBatch(insertStore4);

            String insertStore5 =
                "INSERT INTO STORES VALUES (" +
                "100005, " +
                "ADDRESS(1000, 'Clover_Road', " +
                    "'Happyville', " +
                    "'CA', '90566'), " +
                "COF_ARRAY('Colombian', " +
                    "'French_Roast', " +
                    "'Espresso', " + 
                    "'Colombian_Decaf', " +
                    "'French_Roast_Decaf'), " +
                "(SELECT OID FROM MANAGERS " +
                "WHERE MGR_ID = 000003))";

            stmt.addBatch(insertStore5);

            int [] updateCounts = stmt.executeBatch();

            ResultSet rs = stmt.executeQuery(
                "SELECT * FROM STORES");
            System.out.println("Table STORES after insertion:");
            System.out.println("STORE_NO   " + "LOCATION   " +
                "COF_TYPE   " + "MGR");

            while (rs.next()) {
                int storeNo = rs.getInt("STORE_NO");
                Struct location = (Struct)rs.getObject("LOCATION");
                Object[] locAttrs = location.getAttributes();
                Array coffeeTypes = rs.getArray("COF_TYPE");
                String[] cofTypes = (String[])coffeeTypes.getArray();

                Ref managerRef = rs.getRef("MGR");
                PreparedStatement pstmt = con.prepareStatement(
                    "SELECT MANAGER " +
                    "FROM MANAGERS " +
                    "WHERE OID = ?");
  
                pstmt.setRef(1, managerRef);
                ResultSet rs2 = pstmt.executeQuery();
                rs2.next();
                Struct manager = (Struct)rs2.getObject("MANAGER");
                Object[] manAttrs = manager.getAttributes();
      
                System.out.print(storeNo + "   ");
                System.out.print(
                    locAttrs[0] + " " +
                    locAttrs[1] + " " +
                    locAttrs[2] + ", " +
                    locAttrs[3] + " " +
                    locAttrs[4] + " ");

                for (int i = 0; i < cofTypes.length; i++)
                    System.out.print( cofTypes[i] + " ");
          
                System.out.println(
                    manAttrs[1] + ", " +
                    manAttrs[2]);
        
                rs2.close();
                pstmt.close();
            }

            rs.close();

        } catch(BatchUpdateException b) {
            System.err.println("-----BatchUpdateException-----");
            System.err.println("SQLState:  " + b.getSQLState());
            System.err.println("Message:  " + b.getMessage());
            System.err.println("Vendor:  " + b.getErrorCode());
            System.err.print("Update counts:  ");
            int [] updateCounts = b.getUpdateCounts();

            for (int i = 0; i < updateCounts.length; i++) {
                System.err.print(updateCounts[i] + "   ");
            }
            System.err.println("");

        } catch(SQLException ex) {
            System.err.println("SQLException: " + ex.getMessage());
            System.err.println("SQLState:  " + ex.getSQLState());
            System.err.println("Message:  " + ex.getMessage());
            System.err.println("Vendor:  " + ex.getErrorCode());
        } finally {
            if (stmt != null) { stmt.close(); }
                JDBCTutorialUtilities.closeConnection(con);
            }
        }
    }
}

Problems with the examples? Try Compiling and Running the Examples: FAQs.
Complaints? Compliments? Suggestions? Give us your feedback.

Previous page: Using DISTINCT Data Type
Next page: Using Customized Type Mappings



Spec-Zone.ru - all specs in one place