调用非对象 PHP 帮助上的成员函数 prepare()
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Call to a member function prepare() on a non-object PHP Help
提问by mcbeav
I am trying to write a PHP function. It is very simple. It is just a prepared statement that queries the database, but I can not get this to work. I keep recieving the error Call to a member function prepare() on a non-object. here is the code:
我正在尝试编写一个 PHP 函数。这很简单。这只是一个查询数据库的准备好的语句，但我无法让它工作。我不断收到错误 Call to a member function prepare() 在非对象上。这是代码：
$DBH = new mysqli("host", "test", "123456", "dbname");
function selectInfo($limit, $offset){
$stmt = $DBH->prepare("SELECT * FROM information LIMIT ?,?");
$stmt->bind_param("ii", $limit, $offset);
$stmt->execute();
}
selectInfo();
Any time I call the function i get that error. Can someone please help?
每当我调用该函数时，我都会收到该错误。有人可以帮忙吗？
回答by ircmaxell
It's a scoping error. You're making $DBHa global variable. So when you enter the function, the global variable is not available. You have 5 real options.
这是一个范围错误。您正在创建$DBH一个全局变量。所以当你进入函数时，全局变量是不可用的。您有 5 种实际选择。
1. Use the global keyword
1. 使用 global 关键字
function doSomething() {
global $DBH;
//...
This is not a good idea, since it makes maintenance and testing a PITA. Imagine trying to debug that function call. You now need to go find out where $DBHis defined to try to figure out what's going on...
这不是一个好主意，因为它使维护和测试成为 PITA。想象一下尝试调试该函数调用。您现在需要找出$DBH定义的位置以试图弄清楚发生了什么......
2. Make $DBHa parameter to the function
2.$DBH给函数做一个参数
function doSomething(MySQLi $DBH) {
It has the advantage of being explicit. But it's still not great since the calling code then needs to keep track of the global variable.
它的优点是明确。但这仍然不是很好，因为调用代码需要跟踪全局变量。
3. Create a function to "get" the $DBHobject
3.创建一个函数来“获取”$DBH对象
function getDBH() {
static $DBH = null;
if (is_null($DBH)) {
$DBH = new mysqli(...);
}
return $DBH;
}
function doSomething() {
$DBH = getDBH();
}
This has the advantage of getting around the global variable problem completely. But it's also hard to have multiple connections or re-use any of the code for other connections.
这具有完全解决全局变量问题的优点。但是也很难有多个连接或将任何代码重用于其他连接。
4. Create a class to wrap database access
4.创建一个类来包装数据库访问
class Database {
public function __construct($host, $user, $pass) {
$this->DBH = new MySQli($host, $user, $pass);
}
public function doSOmething() {
$this->DBH->foo();
}
}
This encapsulates everything for you. All database access will go through a single class, so you don't need to worry about global variable access or anything else.
这为您封装了所有内容。所有数据库访问都将通过一个类，因此您无需担心全局变量访问或其他任何事情。
5. Use a pre-built class/framework
5. 使用预先构建的类/框架
This is the best option, since you don't need to worry about doing it yourself.
这是最好的选择，因为您不必担心自己做。
Database Access Classes:
数据库访问类：
- A quick google search to get you started
- Doctrine ORM- A complete database access library with full ORM (Object Mapping)
- ADODB- A database agnostic database access library
- Pear MDB2- Another database access library
- 一个快速的谷歌搜索让你开始
- Doctrine ORM- 具有完整 ORM（对象映射）的完整数据库访问库
- ADODB- 一个与数据库无关的数据库访问库
- Pear MDB2- 另一个数据库访问库
Full Frameworks:
完整框架：
- Zend Framework
- Lithium Framework
- Code Igniter
- (really there are a lot more, I'm not going to bother listing any more since that's another question all together...)
Really, the choices are endless. Find something you like, and stick with it. It really will make your life easier...
真的，选择是无止境的。找到你喜欢的东西，并坚持下去。它真的会让你的生活更轻松......
Good Luck!
祝你好运！
回答by Jim
$DBHis not in scope. You either want to define $DBHas global in the function:
$DBH不在范围内。您要么想$DBH在函数中定义为全局：
$DBH = new mysqli("host", "test", "123456", "dbname");
function selectInfo($limit, $offset){
global $DBH;
$stmt = $DBH->prepare("SELECT * FROM information LIMIT ?,?");
$stmt->bind_param("ii", $limit, $offset);
$stmt->execute();
}
or as ircmaxell pointed out in his excellent answer have a function which returns a static instance of $DBH.
或者正如 ircmaxell 在他的优秀回答中指出的那样，有一个函数可以返回$DBH.
回答by Crozin
That's simply. $DBHdoesn't exist within selectInfo()function. Variable defined in global scope won't be visible within function and vice-versa. Read more about variables scopeon manual pages.
那简直了。$DBH不存在于selectInfo()函数中。在全局范围内定义的变量在函数内不可见，反之亦然。在手册页上阅读有关变量作用域的更多信息。
How to solve it? Pass that variable as a argument of the function:
如何解决？将该变量作为函数的参数传递：
$dbh = new MySQLi(...);
function selectInfo(MySQLi $dbh, $limit, $offset) {
$stmt = $dbh->prepare(...);
...
}
回答by madkris24
Make sure the connection is successful.
确保连接成功。
$DBH = @new mysqli("host", "test", "123456", "dbname");
if ($DBH->connect_errno) {
die('Connect Error: ' . $DBH->connect_errno);
}
or
或者
$DBH = @mysqli_connect("host", "test", "123456", "dbname");
if (!$DBH ) {
die('Connect Error: ' . mysqli_connect_errno());
}
回答by István Ujj-Mészáros
Try to add global $DBH;in the function, or add it to the function's parameters.
尝试global $DBH;在函数中添加，或者将其添加到函数的参数中。
回答by Sandeepan Nath
selectInfo($DBH);
function selectInfo($DBH,$limit, $offset){
$stmt = $DBH->prepare("SELECT * FROM information LIMIT ?,?");
$stmt->bind_param("ii", $limit, $offset);
$stmt->execute();
}
回答by Nami Hamiroo
Making $DBH global is not healthy... except that you can make your $DBH protected in class and set it to null.. and use it..
使 $DBH 全局化是不健康的...除了您可以在类中保护 $DBH 并将其设置为 null .. 并使用它..
回答by Nami Hamiroo
class PDOconnect extends PDO{
protected $con=null;
受保护的 $con=null;
public function __construct(){
try {
$this->con= new PDO( DB_DSN, DB_USERNAME, DB_PASSWORD ); //our new PDO Object
$this->con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT );
$this->con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING );
$this->con->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
echo "hi.. you are connected succcessfully...";
}
