1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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5 <title>Tutorial: Moving from MySQL to ADODB</title>
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9 <h1>Tutorial: Moving from MySQL to ADODB</h1>
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11 <pre> You say eether and I say eyether,
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12 You say neether and I say nyther;
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13 Eether, eyether, neether, nyther -
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14 Let's call the whole thing off !
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16 You like potato and I like po-tah-to,
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17 You like tomato and I like to-mah-to;
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18 Potato, po-tah-to, tomato, to-mah-to -
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19 Let's call the whole thing off !
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21 <p>I love this song, especially the version with Louis Armstrong and Ella singing
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22 duet. It is all about how hard it is for two people in love to be compatible
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23 with each other. It's about compromise and finding a common ground, and that's
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24 what this article is all about.
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25 <p>PHP is all about creating dynamic web-sites with the least fuss and the most
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26 fun. To create these websites we need to use databases to retrieve login information,
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27 to splash dynamic news onto the web page and store forum postings. So let's
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28 say we were using the popular MySQL database for this. Your company has done
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29 such a fantastic job that the Web site is more popular than your wildest dreams.
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30 You find that MySQL cannot scale to handle the workload; time to switch databases.
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31 <p> Unfortunately in PHP every database is accessed slightly differently. To connect
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32 to MySQL, you would use <i>mysql_connect()</i>; when you decide to upgrade to
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33 Oracle or Microsoft SQL Server, you would use <i>ocilogon() </i>or <i>mssql_connect()</i>
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34 respectively. What is worse is that the parameters you use for the different
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35 connect functions are different also.. One database says po-tato, the other
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36 database says pota-to. Oh-oh.
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37 <h3>Let's NOT call the whole thing off</h3>
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38 <p>A database wrapper library such as ADODB comes in handy when you need to ensure portability. It provides
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39 you with a common API to communicate with any supported database so you don't have to call things off. <p>
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41 <p>ADODB stands for Active Data Objects DataBase (sorry computer guys are sometimes
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42 not very original). ADODB currently supports MySQL, PostgreSQL, Oracle, Interbase,
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43 Microsoft SQL Server, Access, FoxPro, Sybase, ODBC and ADO. You can download
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44 ADODB from <a href=http://php.weblogs.com/adodb></a><a href="http://php.weblogs.com/adodb">http://php.weblogs.com/adodb</a>.
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45 <h3>MySQL Example</h3>
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46 <p>The most common database used with PHP is MySQL, so I guess you should be familiar
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47 with the following code. It connects to a MySQL server at <i>localhost</i>,
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48 database <i>mydb</i>, and executes an SQL select statement. The results are
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49 printed, one line per row.
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50 <pre><font color="#666600">$db = <b>mysql_connect</b>("localhost", "root", "password");
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51 <b>mysql_select_db</b>("mydb",$db);</font>
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52 <font color="#660000">$result = <b>mysql_query</b>("SELECT * FROM employees",$db)</font><code><font color="#663300">;
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53 if ($result === false) die("failed");</font></code>
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54 <font color="#006666"><b>while</b> ($fields =<b> mysql_fetch_row</b>($result)) {
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55 <b>for</b> ($i=0, $max=sizeof($fields); $i < $max; $i++) {
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56 <b>print</b> $fields[$i].' ';
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58 <b>print</b> "<br>\n";
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61 <p>The above code has been color-coded by section. The first section is the connection
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62 phase. The second is the execution of the SQL, and the last section is displaying
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63 the fields. The <i>while</i> loop scans the rows of the result, while the <i>for</i>
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64 loop scans the fields in one row.</p>
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65 <p>Here is the equivalent code in ADODB</p>
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66 <pre><b><font color="#666600"> include("adodb.inc.php");</font></b><font color="#666600">
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67 $db = <b>NewADOConnection</b>('mysql');
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68 $db-><b>Connect</b>("localhost", "root", "password", "mydb");</font>
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69 <font color="#663300">$result = $db-><b>Execute</b>("SELECT * FROM employees");
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70 </font><font color="#663300"></font><code><font color="#663300">if ($result === false) die("failed")</font></code><code><font color="#663300">;</font></code>
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71 <font color="#006666"><b>while</b> (!$result->EOF) {
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72 <b>for</b> ($i=0, $max=$result-><b>FieldCount</b>(); $i < $max; $i++)
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73 <b>print</b> $result->fields[$i].' ';
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74 $result-><b>MoveNext</b>();
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75 <b>print</b> "<br>\n";
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76 }</font> </pre>
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78 <p>Now porting to Oracle is as simple as changing the second line to <code>NewADOConnection('oracle')</code>.
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79 Let's walk through the code...</p>
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80 <h3>Connecting to the Database</h3>
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82 <pre><b><font color="#666600">include("adodb.inc.php");</font></b><font color="#666600">
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83 $db = <b>NewADOConnection</b>('mysql');
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84 $db-><b>Connect</b>("localhost", "root", "password", "mydb");</font></pre>
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85 <p>The connection code is a bit more sophisticated than MySQL's because our needs
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86 are more sophisticated. In ADODB, we use an object-oriented approach to managing
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87 the complexity of handling multiple databases. We have different classes to
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88 handle different databases. If you aren't familiar with object-oriented programing,
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89 don't worry -- the complexity is all hidden away in the<code> NewADOConnection()</code>
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91 <p>To conserve memory, we only load the PHP code specific to the database you
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92 are connecting to. We do this by calling <code>NewADOConnection(databasedriver)</code>.
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93 Legal database drivers include <i>mysql, mssql, oracle, oci8, postgres, sybase,
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94 vfp, access, ibase </i>and many others.</p>
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95 <p>Then we create a new instance of the connection class by calling <code>NewADOConnection()</code>.
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96 Finally we connect to the database using <code>$db->Connect(). </code></p>
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97 <h3>Executing the SQL</h3>
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98 <p><code><font color="#663300">$result = $db-><b>Execute</b>("SELECT *
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99 FROM employees");<br>
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100 if ($result === false) die("failed")</font></code><code><font color="#663300">;</font></code>
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103 <p>Sending the SQL statement to the server is straight forward. Execute() will
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104 return a recordset object on successful execution. You should check $result
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106 <p>An issue that confuses beginners is the fact that we have two types of objects
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107 in ADODB, the connection object and the recordset object. When do we use each?
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108 <p>The connection object ($db) is responsible for connecting to the database,
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109 formatting your SQL and querying the database server. The recordset object ($result)
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110 is responsible for retrieving the results and formatting the reply as text or
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112 <p>The only thing I need to add is that ADODB provides several helper functions
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113 for making INSERT and UPDATE statements easier, which we will cover in the Advanced
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115 <h3>Retrieving the Data<br>
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117 <pre><font color="#006666"><b>while</b> (!$result->EOF) {
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118 <b>for</b> ($i=0, $max=$result-><b>FieldCount</b>(); $i < $max; $i++)
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119 <b>print</b> $result->fields[$i].' ';
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120 $result-><b>MoveNext</b>();
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121 <b>print</b> "<br>\n";
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122 }</font></pre>
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123 <p>The paradigm for getting the data is that it's like reading a file. For every
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124 line, we check first whether we have reached the end-of-file (EOF). While not
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125 end-of-file, loop through each field in the row. Then move to the next line
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126 (MoveNext) and repeat.
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127 <p>The <code>$result->fields[]</code> array is generated by the PHP database
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128 extension. Some database extensions do not index the array by field name.
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129 To force indexing by name - that is associative arrays -
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130 use the $ADODB_FETCH_MODE global variable.
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132 $<b>ADODB_FETCH_MODE</b> = ADODB_FETCH_NUM;
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133 $rs1 = $db->Execute('select * from table');
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134 $<b>ADODB_FETCH_MODE</b> = ADODB_FETCH_ASSOC;
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135 $rs2 = $db->Execute('select * from table');
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136 print_r($rs1->fields); // shows <i>array([0]=>'v0',[1] =>'v1')</i>
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137 print_r($rs2->fields); // shows <i>array(['col1']=>'v0',['col2'] =>'v1')</i>
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140 As you can see in the above example, both recordsets store and use different fetch modes
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141 based on the $ADODB_FETCH_MODE setting when the recordset was created by Execute().</p>
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142 <h2>ADOConnection<a name="ADOConnection"></a></h2>
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143 <p>Object that performs the connection to the database, executes SQL statements
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144 and has a set of utility functions for standardising the format of SQL statements
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145 for issues such as concatenation and date formats.</p>
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147 <h3>Other Useful Functions</h3>
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148 <p><code>$recordset->Move($pos)</code> scrolls to that particular row. ADODB supports forward
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149 scrolling for all databases. Some databases will not support backwards scrolling.
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150 This is normally not a problem as you can always cache records to simulate backwards
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152 <p><code>$recordset->RecordCount()</code> returns the number of records accessed by the
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153 SQL statement. Some databases will return -1 because it is not supported.
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154 <p><code>$recordset->GetArray()</code> returns the result as an array.
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155 <p><code>rs2html($recordset)</code> is a function that is generates a HTML table based on the
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156 $recordset passed to it. An example with the relevant lines in bold:
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157 <pre> include('adodb.inc.php');
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158 <b>include('tohtml.inc.php');</b> /* includes the rs2html function */
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159 $conn = ADONewConnection('mysql');
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160 $conn->PConnect('localhost','userid','password','database');
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161 $rs = $conn->Execute('select * from table');
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162 <b> rs2html($rs)</b>; /* recordset to html table */ </pre>
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163 <p>There are many other helper functions that are listed in the documentation available at <a href="http://php.weblogs.com/adodb_manual"></a><a href="http://php.weblogs.com/adodb_manual">http://php.weblogs.com/adodb_manual</a>.
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164 <h2>Advanced Material</h2>
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165 <h3>Inserts and Updates </h3>
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166 <p>Let's say you want to insert the following data into a database.
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167 <p><b>ID</b> = 3<br>
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168 <b>TheDate</b>=mktime(0,0,0,8,31,2001) /* 31st August 2001 */<br>
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169 <b>Note</b>= sugar why don't we call it off
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170 <p>When you move to another database, your insert might no longer work.</p>
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171 <p>The first problem is that each database has a different default date format.
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172 MySQL expects YYYY-MM-DD format, while other databases have different defaults.
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173 ADODB has a function called DBDate() that addresses this issue by converting
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174 converting the date to the correct format.</p>
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175 <p>The next problem is that the <b>don't</b> in the Note needs to be quoted. In
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176 MySQL, we use <b>don\'t</b> but in some other databases (Sybase, Access, Microsoft
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177 SQL Server) we use <b>don''t. </b>The qstr() function addresses this issue.</p>
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178 <p>So how do we use the functions? Like this:</p>
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179 <pre>$sql = "INSERT INTO table (id, thedate,note) values ("
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181 . $db->DBDate($<b>TheDate</b>) .','
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182 . $db->qstr($<b>Note</b>).")";
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183 $db->Execute($sql);</pre>
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184 <p>ADODB also supports <code>$connection->Affected_Rows()</code> (returns the
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185 number of rows affected by last update or delete) and <code>$recordset->Insert_ID()</code>
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186 (returns last autoincrement number generated by an insert statement). Be forewarned
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187 that not all databases support the two functions.<br>
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190 <p>You can find out more information about each of the fields (I use the words
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191 fields and columns interchangebly) you are selecting by calling the recordset
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192 method <code>FetchField($fieldoffset)</code>. This will return an object with
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193 3 properties: name, type and max_length.
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194 <pre>For example:</pre>
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195 <pre>$recordset = $conn->Execute("select adate from table");<br>$f0 = $recordset->FetchField(0);
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197 <p>Then <code>$f0->name</code> will hold <i>'adata'</i>, <code>$f0->type</code>
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198 will be set to '<i>date'</i>. If the max_length is unknown, it will be set to
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200 <p>One problem with handling different databases is that each database often calls
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201 the same type by a different name. For example a <i>timestamp</i> type is called
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202 <i>datetime</i> in one database and <i>time</i> in another. So ADODB has a special
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203 <code>MetaType($type, $max_length)</code> function that standardises the types
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205 <p>C: character and varchar types<br>
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206 X: text or long character (eg. more than 255 bytes wide).<br>
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207 B: blob or binary image<br>
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210 L: logical (boolean)<br>
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212 N: numeric (float, double, money)
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213 <p>In the above date example,
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214 <p><code>$recordset = $conn->Execute("select adate from table");<br>
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215 $f0 = $recordset->FetchField(0);<br>
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216 $type = $recordset->MetaType($f0->type, $f0->max_length);<br>
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217 print $type; /* should print 'D'</code> */
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219 <p><b>Select Limit and Top Support</b>
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220 <p>ADODB has a function called $connection->SelectLimit($sql,$nrows,$offset) that allows
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221 you to retrieve a subset of the recordset. This will take advantage of native
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222 SELECT TOP on Microsoft products and SELECT ... LIMIT with PostgreSQL and MySQL, and
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223 emulated if the database does not support it.
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224 <p><b>Caching Support</b>
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225 <p>ADODB allows you to cache recordsets in your file system, and only requery the database
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226 server after a certain timeout period with $connection->CacheExecute($secs2cache,$sql) and
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227 $connection->CacheSelectLimit($secs2cache,$sql,$nrows,$offset).
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228 <p><b>PHP4 Session Handler Support</b>
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229 <p>ADODB also supports PHP4 session handlers. You can store your session variables
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230 in a database for true scalability using ADODB. For further information, visit
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231 <a href="http://php.weblogs.com/adodb-sessions"></a><a href="http://php.weblogs.com/adodb-sessions">http://php.weblogs.com/adodb-sessions</a>
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232 <h3>Commercial Use Encouraged</h3>
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233 <p>If you plan to write commercial PHP applications that you want to resell, you should consider ADODB. It has been released using the lesser GPL, which means you can legally include it in commercial applications, while keeping your code proprietary. Commercial use of ADODB is strongly encouraged! We are using it internally for this reason.<p>
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235 <h2>Conclusion</h2>
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236 <p>As a thank you for finishing this article, here are the complete lyrics for
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237 <i>let's call the whole thing off</i>.<br>
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242 You say eether and I say eyether,
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243 You say neether and I say nyther;
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244 Eether, eyether, neether, nyther -
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245 Let's call the whole thing off !
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247 You like potato and I like po-tah-to,
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248 You like tomato and I like to-mah-to;
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249 Potato, po-tah-to, tomato, to-mah-to -
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250 Let's call the whole thing off !
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252 But oh, if we call the whole thing off, then we must part.
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253 And oh, if we ever part, then that might break my heart.
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255 So, if you like pajamas and I like pa-jah-mas,
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256 I'll wear pajamas and give up pa-jah-mas.
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258 Need each other, so we
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259 Better call the calling off off.
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260 Let's call the whole thing off !
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264 You say laughter and I say lawfter,
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265 You say after and I say awfter;
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266 Laughter, lawfter, after, awfter -
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267 Let's call the whole thing off !
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269 You like vanilla and I like vanella,
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270 You, sa's'parilla and I sa's'parella;
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271 Vanilla, vanella, choc'late, strawb'ry -
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272 Let's call the whole thing off !
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274 But oh, if we call the whole thing off, then we must part.
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275 And oh, if we ever part, then that might break my heart.
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277 So, if you go for oysters and I go for ersters,
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278 I'll order oysters and cancel the ersters.
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280 Need each other, so we
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281 Better call the calling off off.
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282 Let's call the whole thing off !
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284 <p><font size=2>Song and lyrics by George and Ira Gershwin, introduced by Fred Astaire and Ginger Rogers
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285 in the film "Shall We Dance?" </font><p>
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287 (c)2001-2002 John Lim.
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