cli-jdbc-php

cli-jdbc-php - Database­Connection Libraries Call­Level...

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Unformatted text preview: Database­Connection Libraries Call­Level Interface Java Database Connectivity PHP 1 An Aside: SQL Injection x SQL queries are often constructed by programs. x These queries may take constants from user input. x Careless code can allow rather unexpected queries to be constructed and executed. 2 Example: SQL Injection x Relation Accounts(name, passwd, acct). x Web interface: get name and password from user, store in strings n and p, issue query, display account number. SELECT acct FROM Accounts WHERE name = :n AND passwd = :p 3 User (Who Is Not Bill Gates) Types Name: Password: gates’ -who cares? Comment in Oracle Your account number is 1234­567 4 The Query Executed SELECT acct FROM Accounts WHERE name = ’gates’ --’ AND passwd = ’who cares?’ All treated as a comment 5 Host/SQL Interfaces Via Libraries x The third approach to connecting databases to conventional languages is to use library calls. 1. C + CLI 2. Java + JDBC 3. PHP + PEAR/DB 6 Three­Tier Architecture x A common environment for using a database has three tiers of processors: 1. Web servers ­­­ talk to the user. 2. Application servers ­­­ execute the business logic. 3. Database servers ­­­ get what the app servers need from the database. 7 Example: Amazon x Database holds the information about products, customers, etc. x Business logic includes things like “what do I do after someone clicks ‘checkout’?”  Answer: Show the “how will you pay for this?” screen. 8 Environments, Connections, Queries x The database is, in many DB­access languages, an environment. x Database servers maintain some number of connections, so app servers can ask queries or perform modifications. x The app server issues statements : queries and modifications, usually. 9 Diagram to Remember Environment Connection Statement 10 SQL/CLI x Instead of using a preprocessor (as in embedded SQL), we can use a library of functions.  The library for C is called SQL/CLI = “Call­ Level Interface.”  Embedded SQL’s preprocessor will translate the EXEC SQL … statements into CLI or similar calls, anyway. 11 Data Structures x C connects to the database by structs of the following types: 1. Environments : represent the DBMS installation. 2. Connections : logins to the database. 3. Statements : SQL statements to be passed to a connection. 4. Descriptions : records about tuples from a query, or parameters of a statement. 12 Handles x Function SQLAllocHandle(T,I,O) is used to create these structs, which are called environment, connection, and statement handles.  T = type, e.g., SQL_HANDLE_STMT.  I = input handle = struct at next higher level (statement < connection < environment).  O = (address of) output handle. 13 Example: SQLAllocHandle SQLAllocHandle(SQL_HANDLE_STMT, myCon, &myStat); x myCon is a previously created connection handle. x myStat is the name of the statement handle that will be created. 14 Preparing and Executing x SQLPrepare(H, S, L) causes the string S, of length L, to be interpreted as a SQL statement and optimized; the executable statement is placed in statement handle H. x SQLExecute(H) causes the SQL statement represented by statement handle H to be executed. 15 Example: Prepare and Execute SQLPrepare(myStat, ”SELECT beer, price FROM Sells WHERE bar = ’Joe’’s Bar’”, SQL_NTS); SQLExecute(myStat); This constant says the second argument is a “null­terminated string”; i.e., figure out the length by counting characters. 16 Direct Execution x If we shall execute a statement S only once, we can combine PREPARE and EXECUTE with: SQLExecuteDirect(H,S,L);  As before, H is a statement handle and L is the length of string S. 17 Fetching Tuples x When the SQL statement executed is a query, we need to fetch the tuples of the result. x SQLFetch(H) gets the next tuple from the result of the statement with handle H. 18  A cursor is implied by the fact we executed a query; the cursor need not be declared. Accessing Query Results x When we fetch a tuple, we need to put the components somewhere. x Each component is bound to a variable by the function SQLBindCol.  1 = handle of the query statement. 2 = column number. 4 = address of the variable. This function has 6 arguments, of which we shall show only 1, 2, and 4: 19 Example: Binding x Suppose we have just done SQLExecute(myStat), where myStat is the handle for query SELECT beer, price FROM Sells WHERE bar = ’Joe’’s Bar’ x Bind the result to theBeer and thePrice: SQLBindCol(myStat, 1, , &theBeer, , ); SQLBindCol(myStat, 2, , &thePrice, , ); 20 Example: Fetching x Now, we can fetch all the tuples of the answer by: while ( SQLFetch(myStat) != SQL_NO_DATA) { /* do something with theBeer and CLI macro representing thePrice */ SQLSTATE = 02000 = “failed to find a tuple.” } 21 JDBC x Java Database Connectivity (JDBC) is a library similar to SQL/CLI, but with Java as the host language. x Like CLI, but with a few differences for us to cover. 22 Making a Connection The JDBC classes import java.sql.*; Class.forName(com.mysql.jdbc.Driver); Connection myCon = DriverManager.getConnection(…); Loaded by forName URL of the database your name, and password go here. The driver for mySql; others exist 23 Statements x JDBC provides two classes: 1. Statement = an object that can accept a string that is a SQL statement and can execute such a string. 2. PreparedStatement = an object that has an associated SQL statement ready to execute. 24 Creating Statements x The Connection class has methods to create Statements and PreparedStatements. Statement stat1 = myCon.createStatement(); PreparedStatement stat2 = myCon.createStatement( ”SELECT beer, price FROM Sells ” + ”WHERE bar = ’Joe’ ’s Bar’ ” createStatement with no argument returns ); a Statement; with one argument it returns 25 a PreparedStatement. Executing SQL Statements x JDBC distinguishes queries from modifications, which it calls “updates.” x Statement and PreparedStatement each have methods executeQuery and executeUpdate.  For Statements: one argument: the query or modification to be executed.  For PreparedStatements: no argument. 26 Example: Update x stat1 is a Statement. x We can use it to insert a tuple as: stat1.executeUpdate( ”INSERT INTO Sells ” + ”VALUES(’Brass Rail’,’Bud’,3.00)” ); 27 Example: Query x stat2 is a PreparedStatement holding the query ”SELECT beer, price FROM Sells WHERE bar = ’Joe’’s Bar’ ”. x executeQuery returns an object of class ResultSet – we’ll examine it later. x The query: ResultSet menu = stat2.executeQuery(); 28 Accessing the ResultSet x An object of type ResultSet is something like a cursor. x Method next() advances the “cursor” to the next tuple.  The first time next() is applied, it gets the first tuple.  If there are no more tuples, next() returns the value false. 29 Accessing Components of Tuples x When a ResultSet is referring to a tuple, we can get the components of that tuple by applying certain methods to the ResultSet. x Method getX (i ), where X is some type, and i is the component number, returns the value of that component.  The value must have type X. 30 Example: Accessing Components x Menu = ResultSet for query “SELECT beer, price FROM Sells WHERE bar = ’Joe’ ’s Bar’ ”. x Access beer and price from each tuple by: while ( menu.next() ) { theBeer = Menu.getString(1); thePrice = Menu.getFloat(2); /*something with theBeer and 31 thePrice*/ PHP x A language to be used for actions within HTML text. x Indicated by <? PHP code ?>. x DB library exists within PEAR (PHP Extension and Application Repository).  Include with include(DB.php). 32 Variables in PHP x Must begin with $. x OK not to declare a type for a variable. x But you give a variable a value that belongs to a “class,” in which case, methods of that class are available to it. 33 String Values x PHP solves a very important problem for languages that commonly construct strings as values: x PHP solution: Double quotes means replace; single quotes means don’t.  How do I tell whether a substring needs to be interpreted as a variable and replaced by its value? 34 Example: Replace or Not? $100 = ”one hundred dollars”; $sue = ’You owe me $100.’; $joe = ”You owe me $100.”; x Value of $sue is ’You owe me $100’, while the value of $joe is ’You owe me one hundred dollars’. 35 PHP Arrays x Two kinds: numeric and associative. x Numeric arrays are ordinary, indexed 0,1,…  Example: $a = array(”Paul”, ”George”, ”John”, ”Ringo”); • Then $a[0] is ”Paul”, $a[1] is ”George”, and so on. 36 Associative Arrays x Elements of an associative array $a are pairs x => y, where x is a key string and y is any value. x If x => y is an element of $a, then $a[x] is y. 37 Example: Associative Arrays x An environment can be expressed as an associative array, e.g.: $myEnv = array( ”phptype” => ”oracle”, ”hostspec” => ”www.stanford.edu”, ”database” => ”cs145db”, ”username” => ”ullman”, ”password” => ”notMyPW”); 38 Making a Connection x With the DB library imported and the array $myEnv available: $myCon = DB::connect($myEnv); Function connect in the DB library Class is Connection because it is returned by DB::connect(). 39 Executing SQL Statements x Method query applies to a Connection object. x It takes a string argument and returns a result.  Could be an error code or the relation returned by a query. 40 Example: Executing a Query x Find all the bars that sell a beer given by the variable $beer. Method Concatenation application in PHP $beer = ’Bud’; $result = $myCon->query( ”SELECT bar FROM Sells” . ”WHERE beer = $beer ;”); Remember this variable is replaced by its value. 41 Cursors in PHP x The result of a query is the tuples returned. x Method fetchRow applies to the result and returns the next tuple, or FALSE if there is none. 42 Example: Cursors while ($bar = $result->fetchRow()) { // do something with $bar } 43 ...
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cli-jdbc-php - Database­Connection Libraries Call­Level...

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