Initial Model class

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+<?php
+/**
+ * Provides the model class, an abstract interface to a database table
+ *
+ * @author Camil Staps
+ *
+ * BusinessAdmin: administrative software for small companies
+ * Copyright (C) 2015 Camil Staps (ViviSoft)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Thrown in Model when a table row could not be found
+ */
+class ModelNotFoundException extends Exception {
+}
+
+/**
+ * Thrown in Model when a column cannot be edited
+ */
+class ModelIllegalAccessException extends Exception {
+}
+
+/**
+ * An abstract interface to a database table
+ */
+abstract class Model {
+	/**
+	 * @var string   $table              The database table
+	 * @var string[] $protected_columns  Columns that cannot be edited
+	 * @var string[] $fillable_columns   Columns that can be edited
+	 * @var string   $primary_key        The table's primary key
+	 */
+	public
+		$table             = '',
+		$protected_columns = ['id'],
+		$fillable_columns  = [],
+		$primary_key       = 'id';
+
+	/**
+	 * @var PDO $pdo              A PDO instance for database communication
+	 * @var mixed[] $data         The column values
+	 */
+	protected $pdo, $data;
+
+	public function __construct($pdo, $id) {
+		$this->pdo = $pdo;
+
+		$stmt = $this->pdo->prepare("SELECT * FROM `".$this->table()."` WHERE `{$this->primary_key}`=?");
+		$stmt->execute([$id]);
+		if ($stmt->rowCount() == 0) {
+			throw new Exception("The {$this->table} with id '$id' could not be found.");
+		}
+		$this->data = $stmt->fetch(PDO::FETCH_ASSOC);
+	}
+
+	/**
+	 * Set a column value
+	 *
+	 * @param string $key         The column
+	 * @param mixed $value        The value
+	 *
+	 * @throws PDOException       Database error
+	 *
+	 * @return bool               True iff the value has been changed
+	 */
+	public function __set($key, $value) {
+		if (!in_array($key, $this->fillable_columns)) {
+			throw new ModelIllegalAccessException("Column $key cannot be edited.");
+		}
+		$stmt = $this->pdo->prepare("UPDATE `".$this->table()."` SET `$key`=? WHERE `{$this->primary_key}`=?");
+		$stmt->execute([$this->mutator($value), $this->data[$this->primary_key]]);
+		$this->data[$key] = $value;
+		return $this->rowCount() != 0;
+	}
+
+	/**
+	 * Get a column value
+	 *
+	 * @param string $key         The column
+	 *
+	 * @return mixed              The value
+	 */
+	public function __get($key) {
+		return $this->accessor($key, $this->data[$key]);
+	}
+
+	/**
+	 * Post-__get() hook to modify the value
+	 *
+	 * @param string $key         The column
+	 * @param string $value       The value
+	 *
+	 * @return string             The modified value (default: $value)
+	 */
+	protected function accessor($key, $value) {
+		return $value;
+	}
+
+	/**
+	 * Pre-__set() hook to modify a value
+	 *
+	 * @param string $key         The column
+	 * @param mixed $value        The value
+	 *
+	 * @return string             The modified value (default: $value casted to string)
+	 */
+	protected function mutator($key, $value) {
+		return (string) $value;
+	}
+
+	/**
+	 * Delete the row
+	 *
+	 * @throws PDOException       Database error
+	 *
+	 * @return bool               True iff the row was really deleted
+	 */
+	public function delete() {
+		$stmt = $this->pdo->prepare("DELETE FROM `{$this->table()}` WHERE `{$this->primary_key}`=?");
+		$stmt->execute([$this->data[$this->primary_key]]);
+		return $stmt->rowCount() != 0;
+	}
+
+	/**
+	 * The actual table, after adding prefixes and the like
+	 *
+	 * @return string The database table
+	 */
+	private function table() {
+		return constants::db_prefix . $this->table;
+	}
+}