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102 lines
3.2 KiB
Markdown
102 lines
3.2 KiB
Markdown
# Databases in PHP
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## PHP Data Objects ([PDO][pdo])
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[pdo]: https://www.php.net/manual/en/book.pdo.php
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PDO is the PHP extension for database access through a single API. It supports various databases: MySQL, SQLite, PostgreSQL, Oracle, SQL Server, etc.
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### Database Connection
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```php
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$dsn = "mysql:dbname=<dbname>;host=<ip>";
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$user="<db_user>";
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$password="<db_password>";
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try {
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$pdo = new PDO($dsn, $user, $password); # connect, can throw PDOException
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} catch (PDOException $e) {
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printf("Connection failed: %s\n", $e->getMessage()); # notify error
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exit(1);
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}
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```
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### Queries
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To execute a query it's necessary to "prepare it" with *parameters*.
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```php
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# literal string with markers
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$sql = 'SELECT fields
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FROM tables
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WHERE field <operator> :marker'
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$stmt = $pdo->prepare($sql, $options_array); # returns PDOStatement, used to execute the query
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$stmt->execute([ ':marker' => value ]); # substitute marker with actual value
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# fetchAll returns all matches
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$result = $stmt->fetchAll(); # result as associative array AND numeric array (PDO::FETCH_BOTH)
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$result = $stmt->fetchAll(PDO::FETCH_ASSOC); # result as associative array
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$result = $stmt->fetchAll(PDO::FETCH_NUM); # result as array
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$result = $stmt->fetchAll(PDO::FETCH_OBJ); # result as object of stdClass
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$result = $stmt->fetchAll(PDO::FETCH_CLASS, ClassName::class); # result as object of a specific class
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```
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### Parameter Binding
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```php
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# bindValue
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$stmt = pdo->prepare(sql);
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$stmt->bindValue(':marker', value, PDO::PARAM_<type>);
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$stmt->execute();
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# bindParam
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$stmt = pdo->prepare(sql);
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$variable = value;
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$stmt->bindParam(':marker', $variable); # type optional
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$stmt->execute();
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```
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### PDO & Data Types
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By default PDO converts all results into strings since it is a generic driver for multiple databases.
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Its possible to disable this behaviour setting `PDO::ATTR_STRINGIFY_FETCHES` and `PDO::ATTR_EMULATE_PREPARES` as `false`.
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**NOTE**: `FETCH_OBJ` abd `FETCH_CLASS` return classes and don't have this behaviour.
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```php
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pdo->setAttribute()
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$pdo->setAttribute(PDO::ATTR_STRINGIFY_FETCHES, false);
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$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
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$stmt = $pdo->prepare($sql);
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$stmt->execute([':marker' => value]);
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$result = $stmt->fetchAll(PDO::FETCH_ASSOC);
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```
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### PDO Debug
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```php
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$stmt = $pdo->prepare($sql);
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$stmt->execute([':marker' => value]);
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$result = $stmt->fetchAll(PDO::FETCH_ASSOC);
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$stmt->debugDumpParams(); # print the SQL query that has been sent to the database
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```
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## [SQLite3](https://www.php.net/manual/en/book.sqlite3.php)
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```php
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$db = SQLite3("db_file.sqlite3"); // connection
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$stmt = $db->prepare("SELECT fields FROM tables WHERE field <operator> :marker"); // prepare query
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$stmt->bindParam(":marker", $variable); // param binding
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$result = $stmt->execute(); // retrieve records
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$result->finalize(); // close result set, recommended calling before another execute()
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$records = $results->fetchArray(SQLITE3_ASSOC); // extract records as array (false if no results)
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```
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**NOTE**: Result set objects retrieved by calling `SQLite3Stmt::execute()` on the same statement object are not independent, but rather share the same underlying structure. Therefore it is recommended to call `SQLite3Result::finalize()`, before calling `SQLite3Stmt::execute()` on the same statement object again.
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