primary-key

问题 I am sorry to ask this but I come from codeIgniter and have a really hard time understanding eloquent model insertion. This is a new way of working with models for me. i have read this article and understand some basics now. I have the following example. I have a product which has many attributes but the relevant one is brand and product name. (see the following example tables) products: id(PK),name,description,brand_id brands: id(PK),name Now here comes the problem. I know i can create a new

问题 I have got a table which has an id (primary key with auto increment), uid (key refering to users id for example) and something else which for my question won’t matter. I want to make, lets call it, different auto-increment keys on id for each uid entry. So, I will add an entry with uid 10, and the id field for this entry will have a 1 because there were no previous entries with a value of 10 in uid . I will add a new one with uid 4 and its id will be 3 because I there were already two entried

问题 I have an object that contains an attribute with the type of another object, which I want to treat as Complex Type. public class Location : IModule { public string Id { get; set; } public Coordinate Coordinate { get; set; } } [ComplexType] public class Coordinate { public string Latitude { get; set; } public string Longitude { get; set; } } While adding a migration, I ran into the problem that a primary key is required (exactly what I want to prevent). The entity type Coordinate requires a

问题 I'm developing an application which needs to hold data about distances between two cities. I have created a distance table in the Mysql database which holds the name of the two cities and the distance between them. I have made the two town columns a composite primary key. I'd like the database to restrict the application from making duplicated reversed entries like shown on the screenshot to prevent having different distance values. What would be the best solution to solve this problem? 回答1:

问题 Say I have a class that looks like this: public class MyClass { @Id @Column(name = "ID") private long Id; } I can use a hibernate session to do a get or load on the class like this: MyClass a = (MyClass)session.get(MyClass.class, new Long(100)); However, assume I have a class with multiple columns as the primary key: public MyJoinClass implements Serializable { private static final long serialVersionUID = -5L; @Id @Column(name = "ID") private long id; @Id @Column(name = "EMAIL_ADDRESS_ID")

问题 I have the following SQL: ALTER TABLE dbo.PS_userVariables DROP CONSTRAINT PK_PS_userVariables; ALTER TABLE dbo.PS_userVariables ADD PRIMARY KEY (varnumber, subjectID, userID, datasetID, listid, userVarTitle); Since I have multiple environments, that PK_PS_userVariables constraint name is different on my different databases. How do I write a script that gets that name then adds it into my script? 回答1: While the typical best practice is to always explicitly name your constraints, you can get

问题 I've a PK constraint - a clustered index on two columns - which I am in the process of dropping. The command is still running after an hour. I would have thought that as I am just removing a constraint the operation would be nearly instantaneous. Can someone explain to me what is actually happening under the hood when I drop the PK? 回答1: Clustered index is not "just a constraint", it's a storage method. When you drop it, your data are being reordered from clustered storage to heap storage

问题 I am preparing a model as follows: class SomeModel(models.Model): id = models.BigIntegerField(primary_key=True, null=False, unique=True) But my primary key must be a valid 9+ digit integer value. If I set the start index as 100000000 . then any value generated as id will be 9 digit or greater in length. But django do not support this. How can I implement this with minimum direct interference to django? I am using Django 1.3 and Postgresql 9.1 回答1: I'm not a django user but I think the

问题 Is it possible to make an auto-increment function in MySQL that combines alpha elements and numeric? I have an existing system with keys like QAb99, QAb101, QAd9003, etc. The max numeric portion ranges from 1 to 9999, while the letters begin with QA and range from QAa to QAd, etc. and will eventually pass QAd9999 to QAe1, etc. Is it better to manage generating new keys in SQL or outside of SQL (i.e. php script)? thanks. 回答1: I asked this a while ago. Mysql doesn't do this unfortunately. I'd

问题 like so: Table-student: sID | name 1 -----susan 2 -----morgan 3 -----Ian 4 -----james Primary key = sID the other table like so: Table- friends friendsID | personA | personB 1-----------1-----------3 2------------1-----------2 3-------------2-----------3 4-------------3------------4 Where Primary Key is: friendsID, personA, personB Foreign Key = personA, personB which both refer to sID in students table I want a way of querying the friends table in such a way that the personA and personB