php - "Cannot add or update a child row: a foreign key constraint fails"的问题

Question

我似乎可以修复这个小错误。我有一个动态列表菜单，其中包含俱乐部场所的场所 ID。用户可以在我的网站上添加事件，其中包含以下信息:event_id、event_name、event_venue、event_date、estination_id...等。字段Estamentation_id可以为空，默认为空。

上面的设施_id是表设施(设施_id)的外键。

如果用户要添加的事件发生在某个场所，则用户可以选择选择该场所；如果没有与其连接的场所，则可以将其留空。

例如

    Select
    Crooked Q'z
    The Haven
    Brew Bistro 

我的动态列表菜单代码

<label for="establishment_link"></label>
<select name="establishment_link" id="establishment_link">
<option selected value="" <?php if (!(strcmp("", $row_establishment_list['establishment_id']))) {echo "selected=\"selected\"";} ?>>Select</option>
<?php
    do {  
    ?>
    <option value="<?php echo $row_establishment_list['establishment_id']?>"<?php if (!(strcmp($row_establishment_list['establishment_id'],
    $row_establishment_list['establishment_name']))) {echo "selected=\"selected\"";} ?>><?php echo $row_establishment_list['establishment_name']?></option>
    <?php
    } while ($row_establishment_list = mysql_fetch_assoc($establishment_list));
    $rows = mysql_num_rows($establishment_list);
        if($rows > 0) {
        mysql_data_seek($establishment_list, 0);
        $row_establishment_list = mysql_fetch_assoc($establishment_list);
        }
        ?>
</select>

但是，当我将其留空时，我收到错误:

Cannot add or update a child row: a foreign key constraint fails (`nnl`.`event`, CONSTRAINT `event_ibfk_1` FOREIGN KEY (`establishment_id`) REFERENCES `establishment` (`establishment_id`))

插入语句:

...

$establishment_link= $_POST['establishment_link'];  
$establishment_link= mysql_real_escape_string($establishment_link);

...

$query2 = "INSERT INTO event(user_id, 
                            event_name, 
                            event_description, 
                            event_photo_url, 
                            event_thumb_url, 
                            event_link_url, 
                            event_venue, 
                            event_telephone,    
                            event_email,    
                            establishment_id,                               
                            event_date, 
                            event_time, 
                            event_entrance_fee, 
                            event_guest_appearances, 
                            event_dress_code, 
                            event_other_details) 
                            VALUES  
                            ('$user_id',
                            '$event_name',
                            '$event_description',
                            '$img_large',
                            '$img_thumb',
                            '$event_url',
                            '$event_venue',
                            '$event_telephone',
                            '$event_email',
                            '$establishment_link',                          
                            '$date',
                            '$time',
                            '$event_fee',
                            '$event_guests',
                            '$event_dress',
                            '$event_other')";                           
//Execute query
$qry_result2 = mysql_query($query2) or die(mysql_error());

如何解决这个问题？

Answer 1

向我们展示实际的 sql 插入语句。但我的第一个猜测是这样的:

insert into events(...., establishment_id) values(...., '');

虽然它应该设置为NULL

insert into events(...., establishment_id) values(...., NULL);

或者不在列列表中提及estination_id

insert into events(...) values(...);

[问题编辑后]

大概就是我说的吧。尝试将您的查询更改为:

$query2 = "INSERT INTO event(user_id, 
                        event_name, 
                        event_description, 
                        event_photo_url, 
                        event_thumb_url, 
                        event_link_url, 
                        event_venue, 
                        event_telephone,    
                        event_email,    
                        establishment_id,                               
                        event_date, 
                        event_time, 
                        event_entrance_fee, 
                        event_guest_appearances, 
                        event_dress_code, 
                        event_other_details) 
                        VALUES  
                        ('$user_id',
                        '$event_name',
                        '$event_description',
                        '$img_large',
                        '$img_thumb',
                        '$event_url',
                        '$event_venue',
                        '$event_telephone',
                        '$event_email',
                        ".(empty($establishment_link) ? "NULL" : "'$establishment_link'").",                          
                        '$date',
                        '$time',
                        '$event_fee',
                        '$event_guests',
                        '$event_dress',
                        '$event_other')";