unique-key

问题 I'm using Python 3.7, Django 2.2, the Django rest framework, and pytest. I have the following model, in which I want to re-use an existing model if it exists by its unique key ... class CoopTypeManager(models.Manager): def get_by_natural_key(self, name): return self.get_or_create(name=name)[0] class CoopType(models.Model): name = models.CharField(max_length=200, null=False, unique=True) objects = CoopTypeManager() Then I have created the below serializer to generate this model from REST data

问题 I have my table users: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------------+--------------+------+-----+---------+-------+ | userid | varchar(30) | YES | | NULL | | | lname | varchar(40) | YES | | NULL | | | fname | varchar(20) | YES | | NULL | | | system_id | varchar(12) | YES | | NULL | | +--------------------+--------------+------+-----+---------+-------+ and I want to change the system_id and the userid

问题 We can have more than one candidate key in a relation. But can we have two candidate keys in a relation different in length? Suppose I have a relation R(A,B,C,D,E) and we have only two sets of attributes which uniquely identify a tuple in the relation: {A,B,C} and {D,E}. So can we say both {A,B,C} and {D,E} are candidate keys? 回答1: But can we have two candidate keys in a relation different in length? Yes. A CK (candidate key) is a superkey (unique column set) that doesn't contain a smaller

问题 I have an index named LocationIndex in solr with fields as follows: <fields> <field name="solr_id" type="string" stored="true" required="true" indexed="true"/> <field name="solr_ver" type="string" stored="true" required="true" indexed="true" default="0000"/> // and some more fields </fields> <uniqueKey>solr_id</uniqueKey> But now I want to change schema so that unique key must be composite of two already present fields solr_id and solr_ver ... something as follows: <fields> <field name="solr

问题 I have an index named LocationIndex in solr with fields as follows: <fields> <field name="solr_id" type="string" stored="true" required="true" indexed="true"/> <field name="solr_ver" type="string" stored="true" required="true" indexed="true" default="0000"/> // and some more fields </fields> <uniqueKey>solr_id</uniqueKey> But now I want to change schema so that unique key must be composite of two already present fields solr_id and solr_ver ... something as follows: <fields> <field name="solr

问题 I had a custom primary key that need to be set up on a particular data in a model. This was not enough, as an attempt to insert a duplicate number succeeded. So now when i replace primary_key=True to unique=True it works properly and rejects duplicate numbers!!. But according this document ( which uses fields ). primary_key=True implies null=False and unique=True. Which makes me confused as in why does it accept the value in the first place with having an inbuilt unique=True ? Thank you.

问题 I had a custom primary key that need to be set up on a particular data in a model. This was not enough, as an attempt to insert a duplicate number succeeded. So now when i replace primary_key=True to unique=True it works properly and rejects duplicate numbers!!. But according this document ( which uses fields ). primary_key=True implies null=False and unique=True. Which makes me confused as in why does it accept the value in the first place with having an inbuilt unique=True ? Thank you.

问题 I have used someone else's code that uses the ipaddress way. However, I would like to use a code that checks for the current userid and the id number. $ipaddress = md5($_SERVER['REMOTE_ADDR']); // here I am taking IP as UniqueID but you can have user_id from Database or SESSION /* Database connection settings */ $con = mysqli_connect('localhost','root','','database'); if (mysqli_connect_errno()) { echo "<p>Connection failed:".mysqli_connect_error()."</p>\n"; } /* end of the connection */ if

问题 How I can assign a sequence value to a field "UID" which is NUll in existing sqlite table, for example table: FOO name UID A 1 B 2 C 100 D NULL E NULL F NULL what I want is table: FOO name UID A 1 B 2 C 100 D 101 E 102 F 103 Can some body help? I want to seek an alternative for using autoincrement on my own reason... thanks! 回答1: Register a function that returns the number of times it's called, and then do UPDATE FOO SET UID = 100 + increment() WHERE UID IS NULL 回答2: a drafted approach in my

问题 This is a question that arose from the consequences of another question here: Is it better to have two separate user tables or one? Assuming I have two types of users, an Author and a Reader, each stored in relational tables keyed to a main Accounts table like so: TABLE Accounts { id email password salt created modified } TABLE reader { id user_id ... } TABLE author { id user_id ... } When an Author posts a blog, should I tag the blog with the unique id from the Authors table, or the unique