mysql default value error - mysql

Question

I'm testing a link-shortener Sinatra application that uses a mysql database. When I enter a link to be shortened, I'm getting this mysql error
(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')
I'm assuming that means field link_identifier should have a default value
urls and visits tables both have link_identifier field, but the links table doesn't. However, in the code that creates the tables, copied below, it's the Link class that has the `property :identifier.' Does anyone know how I would fix this problem?
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 | |
+------------+-------------+------+-----+---------+-------+
Code
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
....
Update - the source code already seems to have a way to create a link identifier to satisfy the requirements of mysql, but it doesn't seem to be working
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

The error means you are not setting a value for link_identifier in your insert statement. And link_identifier cannot be null by table definition.
You need to specify a value for link_identifier. Example
INSERT INTO `urls` (`original`, `link_identifier`)
VALUES ('http://pryrepl.org/screencasts.html', 'value_for_link_identifier')

Answer 2

When sending the query
INSERT INTO `urls` (`original`) VALUES ('http://pryrepl.org/screencasts.html')
the value for link_identifier isn't set.
You defined the urls table as
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)
The default value for link_identifier is NULL (or not set), but since the value cannot be NULL, mysql doesn't know what to set as value.
Change the mysql query into
INSERT INTO `urls` (`original`, `link_identifier`) VALUES ('http://pryrepl.org/screencasts.html', '<your identifier here>')