如何在子表oophp中使用外键插入

Question

UPDATE : I have two tables users And requests users table has columns id username,password and town i can insert data in users successfully .requests table has id ,user_id ,product_name, proposed_price and request_description , where user_id is a foreign key referencing id from users table, the problem is that insert data fails in requests table which has user_id as a foreign key . i get nothing in requests table

This function is supposed to be used in insertion:

    public function  User_request ($product_name, $proposed_price, $request_description) {

     $qry = $this->conn->prepare("SELECT id FROM users WHERE id = ? ");
     $qry->bind_param("i", id);
     $result= $qry->execute();
     $user_id = $qry->fetch();
     $qry->close();

    if($user_id > 0){

    $stmt = $this->conn->prepare("INSERT INTO  requests (user_id, product_name, proposed_price, request_description) VALUES(?, ?, ?, ?)");

    $stmt->bind_param("isss",$user_id, $product_name, $proposed_price, $request_description);
    $result = $stmt->execute();
    $stmt->close();

    // check for successful store
    if ($result) {
        $stmt = $this->conn->prepare("SELECT * FROM requests WHERE request_description = ?");
        $stmt->bind_param("s", $request_description);
        $stmt->execute();
        $user = $stmt->get_result()->fetch_assoc();
        $stmt->close();

        return $user;
    } else {
        return false;
    }

    }
} 

And below codes call above function:

       <?php

  include './DbHandler.php';
  $db = new DBHandler();

   // json response array
  $response = array("error" => FALSE);

 if ( isset($_POST['product_name']) && isset($_POST['proposed_price']) &&        isset($_POST['request_description']) ) {

// receiving the post params
$product_name = $_POST['product_name'];
$proposed_price =$_POST['proposed_price'];
$request_description =$_POST['request_description'];

    // create a new request
    $user = $db-User_request($product_name, $proposed_price,    $request_description);
    if ($user) {
        // user stored successfully
        $response["error"] = FALSE;
        $response["user"]["username"] = $user["username"];
        $response["user"]["proposed_price"] = $user["proposed_price"];
        $response["user"]["request_description"] = $user["request_description"];

        echo json_encode($response);
    } else {
        // user failed to store
        $response["error"] = TRUE;
        $response["error_msg"] = "oops error occured!";
        echo json_encode($response);
    }
}
   else {
     $response["error"] = TRUE;
      $response["error_msg"] = "Required parameters are missing!";
     echo json_encode($response);
   }
  ?>

Answer 1

Clearly, the problem is that you have a foreign key pointing to the user issuing the request and when you try to insert to that table , you get an exception since the foreign key is not nullable. There are two possible solutions: you either find the proper user and use its id as user_id in the insert statement, or you modify the foreign key column to be nullable, so you support user-less requests.

So, the first solution is to:

• pass the user_id to User_request function
• modify User_request 's parameter list by adding $user_id there
• modify your insert statement and add $user_id as the fourth parameter

The second solution is to alter the table so that user_id to allow null s. I believe you need the first solution.

EDIT:

I believe this line:

$user = $db-User_request($product_name, $proposed_price,    $request_description);

is

$user = $db->User_request($product_name, $proposed_price,    $request_description);

Also, you have this value: $user["username"]

I am not sure about the name of the user table, but will assume it is called users and has an id and a username field, so a query like:

select id, username from users where username = ?

would return the relevant data and you could implement a function called getUserByUsername which will take a username , which will be $user["username"] in our case and return the user (note, that this is better read from $_SESSION , but I do not know what you have there). From here you can read user_id and you will be able to pass it as:

//I left the name user here, but you essentially gather a request record
$user = $db->User_request($product_name, $proposed_price,    $request_description, $user_id);

and the other function would change to:

         //I left the name user here, but you essentially gather a request record
         public function  User_request ($product_name, $proposed_price, $request_description, $user_id) {



    //Notice the fourth ? and user_id at the end of the liist
    $stmt = $this->conn->prepare("INSERT INTO  requests ( product_name, proposed_price, request_description, user_id) VALUES(?, ?, ?, ?)");

    //and you need the effective value as well
    $stmt->bind_param("sss", $product_name, $proposed_price, $request_description, $user_id);
    $result = $stmt->execute();
    $stmt->close();

    // check for successful store
    if ($result) {
        $stmt = $this->conn->prepare("SELECT * FROM requests WHERE request_description = ?");
        $stmt->bind_param("s", $request_description);
        $stmt->execute();
        $user = $stmt->get_result()->fetch_assoc();
        $stmt->close();

        return $user;
    } else {
        return false;
    }
}