accessing a database using sqlj

Copyright Oracle Corporation, 1998. All rights reserved.

77

Accessing a Database Using SQLJ

Accessing a Database Using SQLJ

Copyright Oracle Corporation, 1998. All rights reserved. 7-7-22

ObjectivesObjectives

After completing this lesson, you should be able to do the following:

• Describe the design goals of SQLJ

• Connect to a database using SQLJ

• Perform DML and DDL operations

• Use AppBuilder for Java to precompile SQLJ code

After completing this lesson, you should be able to do the following:

• Describe the design goals of SQLJ


• Perform DML and DDL operations

• Use AppBuilder for Java to precompile SQLJ code


OverviewOverview

Java file compiled

SQL code first parse

Development Development timetime

Run timeRun time

Java with Java with JDBCJDBC SQLJSQLJ

Java file compiled

SQLJ file pre-

compiledSQL code first parse

SQL

JDBC


SQLJ is passed through a precompiler:

• Checks SQL against the database

• Generates Java code with JDBC calls

SQLJ is passed through a precompiler:

• Checks SQL against the database

• Generates Java code with JDBC calls

Using SQLJUsing SQLJ

SQLJ codeJava code

withJDBC calls

Java compiler

SQLJpreprocessor

OracleRegular

Java class


Design Goals of SQLJDesign Goals of SQLJ

• Allows easy embedding of SQL statements in Java source code

– More concise than JDBC

• Early checking of SQL statements eliminates many run time errors:

– SQL syntax errors

– Incorrect assumption of table structures

– Java/SQL type mismatch

• Allows easy embedding of SQL statements in Java source code

– More concise than JDBC

• Early checking of SQL statements eliminates many run time errors:

– SQL syntax errors

– Incorrect assumption of table structures

– Java/SQL type mismatchSQL


What Does SQLJ Look Like?What Does SQLJ Look Like?

SQL code is embedded in Java code

• File typically has a .sqlj extension

• Equivalent code using JDBC:

SQL code is embedded in Java code

• File typically has a .sqlj extension

• Equivalent code using JDBC:

void myJavaMethod() {

#sql { create table EMP(EMPNO number(5) };

}


Statement st = conn.createStatement();

st.execute("create table EMP(EMPNO number(5))");

}

myfile.sqlj

another.java


• Imports needed

• SQLJ statementbegins with#sql

• SQL statement placed in braces - can throw SQLException

• Imports needed

• SQLJ statementbegins with#sql

• SQL statement placed in braces - can throw SQLException

SQLJ Syntax: A Closer LookSQLJ Syntax: A Closer Look

import java.sql.*;

import sqlj.runtime.*;

import sqlj.runtime.ref.*;

class X {


try {

#sql{update EMP

set SAL = SAL + 100

where SAL < 1500};

}

catch (SQLException e) {…}

}


Loading the JDBC DriverLoading the JDBC Driver

• SQLJ requires that the JDBC driver class is loaded

• This can be performed in the same way as for JDBC:

• SQLJ requires that the JDBC driver class is loaded

• This can be performed in the same way as for JDBC:

try { Class.forName("oracle.jdbc.driver.OracleDriver");}catch (ClassNotFoundException e) { System.out.println("Could not load the driver");}


Specifying a Connection Context

Specifying a Connection Context

All SQLJ statements execute in a “connection context”

• Defines the database schema, session, and transaction

All SQLJ statements execute in a “connection context”

• Defines the database schema, session, and transactiontry { Class.forName(…);

DefaultContext.setDefaultContext( new DefaultContext( "jdbc:oracle:thin:@HOSTID:1521:ORCL", "theUser", "thePassword") ); }catch (Exception e) {…}


Once the JDBC driver has been loaded, and a connection context has been set, SQLJ statements can be executed

Once the JDBC driver has been loaded, and a connection context has been set, SQLJ statements can be executed

Executing the SQL StatementExecuting the SQL Statement

try { Class.forName(…); DefaultContext.setDefaultContext(…);

#sql { update EMP

set SAL = SAL + 100

where SAL < 1500 };

}catch (Exception e) {…}


Passing Host Variables into a SQLJ Statement

Passing Host Variables into a SQLJ Statement

• A host variable is a variable in your Java program

• Host variables can be used in a SQLJ statement as follows:

• A host variable is a variable in your Java program

• Host variables can be used in a SQLJ statement as follows:

void deleteHighEarners(BigDecimal amt){ try { #sql {delete from EMP where SAL >= :amt}; } catch (SQLException e) {…}}


Guided Practice: SQLJ and JDBC

Guided Practice: SQLJ and JDBC

This example uses JDBC to give a pay raise to selected employees.

• How would it look in SQLJ?

This example uses JDBC to give a pay raise to selected employees.

• How would it look in SQLJ?BigDecimal amt, low;… Class.forName(…);Connection conn = DriverManager.getConnection(…); PreparedStatement stmt = conn.prepareStatement ("update EMP set SAL = SAL + ? where SAL < ?");stmt.setBigDecimal(1, amt);stmt.setBigDecimal(2, low);stmt.execute();


Assigning Results to Host Variables

Assigning Results to Host Variables

Host variables can be assignment targets, for values retrieved by SQL operationsHost variables can be assignment targets, for values retrieved by SQL operations

void printJobTitle(BigDecimal empno) {

String job; try { #sql { select JOB into :job from EMP where EMPNO = :empno };

System.out.println("Job title is " + job); } catch (SQLException e) {}}


Dealing with Query Result SetsDealing with Query Result Sets

• SQLJ can be used to execute queries that return a result set

• To process the result set, define an “iterator” type

– Specifies the data type of each column

– Use the iterator to retrieve columns

• SQLJ can be used to execute queries that return a result set

• To process the result set, define an “iterator” type

– Specifies the data type of each column

– Use the iterator to retrieve columns

… select ENAME, SAL from EMP …


Defining a Named IteratorDefining a Named Iterator

• An iterator type can be defined as shown here, to retrieve columns byname:

• SQLJ translates this into a Java class called MyIter, with these methods:

• An iterator type can be defined as shown here, to retrieve columns byname:

• SQLJ translates this into a Java class called MyIter, with these methods:

#sql iterator MyIter(String ENAME, String JOB);

String ENAME()… // Get ENAME column

String JOB()… // Get JOB column

boolean next()… // Go to next row


Using a Named IteratorUsing a Named Iterator

The iterator can be used to extract columns by name, in a type-safe mannerThe iterator can be used to extract columns by name, in a type-safe manner

#sql iterator MyIter(String ENAME, String JOB);

class MyClass {

void aMethod() { MyIter iter; #sql iter = { select ENAME, JOB from EMP };

while(iter.next()) { String ename = iter.ENAME(); String job = iter.JOB(); } …


Defining By-Position IteratorsDefining By-Position Iterators

• By-position iterators define the type of each column, but not a name

• Columns must be fetched by position:

• By-position iterators define the type of each column, but not a name

• Columns must be fetched by position:

#sql iterator MyIter(String, String);… MyIter iter; String name, job; #sql iter = { select ENAME, JOB from EMP };

while(true) { #sql {fetch :iter into :name, :job}; if (iter.endFetch()) break; System.out.println(name + " is a " + job); …


Calling Stored Procedures and Stored Functions

Calling Stored Procedures and Stored Functions

• A SQLJ statement can call a stored procedure as follows:

• Stored functions are called as follows:

• A SQLJ statement can call a stored procedure as follows:

• Stored functions are called as follows:

String ename = …;

#sql { call PayBonus(:ename, 100) };

String dname = …;BigDecimal topSal;

#sql topSal = { values( GetTopSal(:dname) ) };


Specifying a Different Database ConnectionSpecifying a Different Database Connection

A different connection context can be specified for SQLJ statements:A different connection context can be specified for SQLJ statements:

#sql context MyDBContext;

class MyClass { void aMethod() { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); MyDBContext ctxt = new MyDBContext( "jdbc:odbc:MyOtherDb", "user", "password");

#sql (ctxt) { select * from TABLEX }; … ctxt.close();


Using SQLJ in AppBuilderUsing SQLJ in AppBuilder

.sqlj files can be added directly to an AppBuilder project.sqlj files can be added directly to an AppBuilder project


Enabling Compile-Time SQL Checking

Enabling Compile-Time SQL Checking

Select Project—>Project Properties from Menu bar

Check this check box

Select Project—>Project Properties from Menu bar

Check this check box


Specifying Connection Properties

Specifying Connection Properties


SummarySummary

• SQLJ enables you to embed SQL statements directly in Java code

• SQLJ statements are compiled statically, whereas JDBC is dynamic

• SQLJ statements begin with #sql

• Iterators and contexts can be defined

– #sql iterator

– #sql context

• SQLJ enables you to embed SQL statements directly in Java code

• SQLJ statements are compiled statically, whereas JDBC is dynamic

• SQLJ statements begin with #sql

• Iterators and contexts can be defined

– #sql iterator

– #sql context


Practice 7-1 OverviewPractice 7-1 Overview

• Create and build SQLJ files using AppBuilder tools


• Create and execute a query using SQJL

• Iterate a result set

• Perform an update operation

• Perform an update operation with parameters

• Create and build SQLJ files using AppBuilder tools


• Create and execute a query using SQJL

• Iterate a result set

• Perform an update operation

• Perform an update operation with parameters

accessing a database using sqlj

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