外键编辑

Question

为什么我第一次编辑外键时它允许我编辑它的值然后在第二次尝试后它会出现这样的错误

Cannot add or update a child row: a foreign key constraint fails (`sadsystem/products`, CONSTRAINT `products_ibfk_3` FOREIGN KEY (`size_id`) REFERENCES `product_sizes` (`size_id`) ON DELETE CASCADE ON UPDATE CASCADE)

你可以看到我的编辑查询

if($mode=="editproduct") 
{
$product_id=$_GET["product_id"];
$sql="SELECT * FROM products WHERE product_id='$product_id'";
$result=mysql_query($sql,$connection) or die(mysql_error());
while($row=mysql_fetch_array($result)) {
$product_id=$row['product_id'];
$product_name=$row['product_name'];
$product_color=$row['product_color'];
$size_id=$row['size_id'];
$product_description=$row['product_description'];
$brand_id=$row['brand_id'];
$category_id=$row['category_id'];
$supplier_id=$row['supplier_id'];
$product_standardPrice=$row['product_standardPrice'];
$product_unitPrice=$row['product_unitPrice'];
} ?>
<link href="default.css" rel="stylesheet" type="text/css">
<form method="post" action="forms.php">
<table align="center">
<tr>
<td><strong>Edit Product</strong></td>
<td><input type="hidden" name="product_id" value="<? echo $product_id ;?>" /></td>
</tr>
<tr>
<td>Product Name</td>
<td><input type="text" name="product_name" value="<? echo $product_name ;?>" /></td>
</tr>
<tr>
<td>Color</td>
<td><input type="text" name="product_color" value="<? echo $product_color ;?>" /></td>
</tr>
<tr>
<td>Size</td>
<td>
<?
    $query="SELECT * FROM product_sizes ORDER BY size_id ASC";
    $result = mysql_query ($query);
    echo "<select name=size_id>";
    while($nt=mysql_fetch_array($result))
    {
    echo "<option value=$nt[$size_id]>$nt[size_name]</option>";
    }
    echo "</select>";
?>
</td>
</tr>
<tr>
<td>Description</td>
<td><input type="text" name="product_description" value="<? echo $product_description ;?>" /></td>
</tr>
<tr>
<td>Brand</td>
<td>
<?
    $query="SELECT * FROM brands ORDER BY brand_name ASC";
    $result = mysql_query ($query);
    echo "<select name=brand_id>";
    while($nt=mysql_fetch_array($result))
    {
    echo "<option value=$nt[brand_id]>$nt[brand_name]</option>";
    }
    echo "</select>";
?>
</td>
</tr>
<tr>
<td>Category</td>
<td>
<?
    $query="SELECT * FROM categories ORDER BY category_name ASC";
    $result = mysql_query ($query);
    echo "<select name=category_id>";
    while($nt=mysql_fetch_array($result))
    {
    echo "<option value=$nt[category_id]>$nt[category_name]</option>";
    }
    echo "</select>";
?>
</td>
</tr>
<tr>
<td>Supplier</td>
<td>
<?
    $query="SELECT * FROM suppliers ORDER BY supplier_name ASC";
    $result = mysql_query ($query);
    echo "<select name=supplier_id>";
    while($nt=mysql_fetch_array($result))
    {
    echo "<option value=$nt[supplier_id]>$nt[supplier_name]</option>";
    }
    echo "</select>";
?>
</td>
</tr>
<tr>
<td>Standard Price</td>
<td><input type="text" name="product_standardPrice" value="<? echo $product_standardPrice ;?>"/></td>
</tr>
<tr>
<td>Unit Price</td>
<td><input type="text" name="product_unitPrice" value="<? echo $product_unitPrice ;?>" /></td>
</tr>
<tr>
<td><input type="submit" name="editproduct" value="Save" /></td>
</tr>
</table>
</form>
<? }

Answer 1

Cannot add or update a child row: a foreign key constraint fails (`sadsystem/products`, CONSTRAINT `products_ibfk_3` FOREIGN KEY (`size_id`) REFERENCES `product_sizes` (`size_id`) ON DELETE CASCADE ON UPDATE CASCADE)

此消息告诉您无法执行您尝试执行的操作，因为它违反了外键约束。

您需要评估您的查询以验证您不是：

（a）在sadsystem/products（也指执行插入，更新或删除）之前在外键表中添加新值（

）。

（b）尝试从外键表中删除一个值，同时将其链接到另一个依赖于该值的表。

（c）其他一些模糊的问题。