mysql默认值错误

Question

我正在测试一个使用 mysql 数据库的链接缩短器 Sinatra 应用程序。当我输入要缩短的链接时，我收到了这个 mysql 错误

 (mysql_errno=1364, sql_state=HY000) Field 'link_identifier' doesn't have a default value Query: INSERT INTO `urls` (`original`) VALUES ('http://pryrepl.org/screencasts.html')

我假设这意味着字段 link_identifier 应该有一个默认值

urls 和visits 表都有link_identifier 字段，但是links 表没有。但是，在创建表的代码中，复制到下面，它是具有“属性：标识符”的 Link 类。有谁知道我将如何解决这个问题？

mysql> show columns from urls;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| id              | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| original        | varchar(255)     | YES  |     | NULL    |                |
| link_identifier | varchar(50)      | NO   | MUL | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
3 rows in set (0.12 sec)

mysql> show columns from visits
    -> ;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| id              | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| created_at      | datetime         | YES  |     | NULL    |                |
| ip              | varchar(39)      | YES  |     | NULL    |                |
| country         | varchar(50)      | YES  |     | NULL    |                |
| link_identifier | varchar(50)      | NO   | MUL | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
5 rows in set (0.08 sec)

mysql> show columns from links
    -> ;
+------------+-------------+------+-----+---------+-------+
| Field      | Type        | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| identifier | varchar(50) | NO   | PRI | NULL    |       |
| created_at | datetime    | YES  |     | NULL    |       |
+------------+-------------+------+-----+---------+-------+

代码

class Url
  include DataMapper::Resource
  property  :id,          Serial
  property  :original,    String, :length => 255   
  belongs_to  :link
end
....

class Link
  include DataMapper::Resource
  property  :identifier,  String, :key => true
  property  :created_at,  DateTime 
  has 1, :url
  has n, :visits

...

class Visit
  include DataMapper::Resource

  property  :id,          Serial
  property  :created_at,  DateTime
  property  :ip,          IPAddress
  property  :country,     String
  belongs_to  :link

  after :create, :set_country

....

更新 - 源代码似乎已经有办法创建一个链接标识符来满足 mysql 的要求，但它似乎没有工作

def self.create_link(original)
    url = Url.create(:original => original)
    if Link.first(:identifier => url.id.to_s(36)).nil? or !DIRTY_WORDS.include? url.id.to_s(36)
      link = Link.new(:identifier => url.id.to_s(36))
      link.url = url
      link.save 
      return link     
    else
      create_link(original)
    end    
  end
end

Answer 1

错误意味着您没有在插入语句中为link_identifier 设置值。而link_identifier 不能是表定义的null。

您需要为link_identifier 指定一个值。示例

INSERT INTO `urls` (`original`, `link_identifier`) 
VALUES ('http://pryrepl.org/screencasts.html', 'value_for_link_identifier')

Answer 2

发送查询时

 INSERT INTO `urls` (`original`) VALUES ('http://pryrepl.org/screencasts.html')

link_identifier 的值未设置。

您将 urls 表定义为

mysql> show columns from urls;
+-----------------+------------------+------+-----+---------+----------------+
| Field           | Type             | Null | Key | Default | Extra          |
+-----------------+------------------+------+-----+---------+----------------+
| id              | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| original        | varchar(255)     | YES  |     | NULL    |                |
| link_identifier | varchar(50)      | NO   | MUL | NULL    |                |
+-----------------+------------------+------+-----+---------+----------------+
3 rows in set (0.12 sec)

link_identifier 的默认值为 NULL（或未设置），但由于该值不能为 NULL，mysql 不知道该设置为什么值。

把mysql查询改成

 INSERT INTO `urls` (`original`, `link_identifier`) VALUES ('http://pryrepl.org/screencasts.html', '<your identifier here>')