primary-key

问题 I am still new in EF code first, so please be lenient with me. I have these entity classes: public class User { public int UserId { get; set; } public string UserName { get; set; } public string EmailAddress { get; set; } public string Password { get; set; } public virtual ICollection<Task> Tasks { get; set; } public virtual ICollection<Task> TaskAssignees { get; set; } public User() { Tasks = new List<Task>(); } } public class Task { public int TaskId { get; set; } public string Name { get;

问题 With the following entity relationship structure I'm struggling to figure out if the relationship between the LOAN and ITEM entities is valid? The weak entity of LOAN uses a partial key of 'loan_dateLeant' and the primary keys from CUSTOMER and ITEM to form LOANs primary key. However LOAN has a 'one to many' relationship with ITEM as a loan can consist of more than one item. But surely this means that if more than one item is loaned, then the loan record will have two item_id values for part

问题 I have questions about What are the benefits of using a one-to-one association on foreign key or a one-to-one association on the primary key ? I've read the documentation of Hibernate available at: http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/associations.html#assoc-unidirectional-121 Can someone tell me with details the plus of using the first or the second implementation? Another question, I have a one-to-one unidirectional relationship between User and Perimeter. (User ---->

问题 I am designing forum database using InnoDB and got few questions , Could any one please help me to clarify them? Posts and Comments table design below CREATE TABLE `my_posts` ( `forum_id` mediumint(8) unsigned NOT NULL, `post_id` int(10) unsigned NOT NULL, // not an auto increment subject varchar(200) NOT NULL, `details` text NOT NULL, `access` tinyint(3) unsigned NOT NULL, //private,friends,public `created_by` int(10) unsigned NOT NULL, `created_on` int(10) unsigned NOT NULL, `updated_on`

问题 I am trying to redifine primary key to existing IDs, but with Apache CXF plugin generation from wsdl file. wsdl file is here - https://api.mindbodyonline.com/0_5/ClientService.asmx?wsdl my pom.xml: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>MindBodyCXF</groupId> <artifactId>CXFSpring<

问题 What meaning does the concept of a primary key have to the database engine of SQL Server? I don't mean the clustered/nonclustered index created on the "ID" column, i mean the constraint object "primary key". Does it matter if it exists or not? Alternatives: alter table add primary key clustered alter table create clustered index Does it make a difference? 回答1: In general, a KEY is a column (or combination of columns) that uniquely identifies each row in the table. It is possible to have

问题 I need a query (INFORMATION_SCHEMA) which will for given schema and table name show me all table columns with following attributes (what key type it is: PK=>Primary Key, UQ=>Unique Key, FK=>Foreign Key, what is key name, and if it is Foreign Key what schema.table.column is referenced): COLUMN_NAME | DATA_TYPE | KEY_TYPE | KEY_NAME | REFERENCED ============+===========+==========+=============+======================== empid | int | PK | PRIMARY | empname | varchar | UQ | uq_empname | empactive

问题 I am creating a webpage. This webpage stores data into a MySQL database based on the users actions. The database has many rows. The primary key of the row is the column rowID and it just numbers the rows in order (e.g. 1, 2, 3, 4....). The user has the option to delete rows. The problem is that when the user deletes rows other than the last row. There is a skip in the rowID. For example, if there are 5 rows, 1, 2, 3, 4 ,5 and the user deletes the third row. Now the data in the rowID column is

问题 I'm doing maintenance work on an existing Rails site and am having some problems stemming from many-to-many associations. It looks like the site was initially built using has_and_belongs_to_many for a few relationships that have since gotten more complicated in the business logic, so I need to use has_many :through instead to support additional fields in the relationship table. However, the join table that was initially used for HABTM doesn't have a primary key, and I've got to add one to

问题 I create a view with following codes SELECT CONVERT(NVARCHAR, YEAR(okuma_tarihi)) + 'T1' AS sno, YEAR(okuma_tarihi) AS Yillar, SUM(toplam_kullanim_T1) AS TotalUsageValue, 'T1' AS UsageType FROM TblSayacOkumalari GROUP BY CONVERT(NVARCHAR, YEAR(okuma_tarihi)) + 'T1', YEAR(okuma_tarihi) UNION ALL SELECT CONVERT(NVARCHAR, YEAR(okuma_tarihi)) + 'T2' AS sno, YEAR(okuma_tarihi) AS Yillar, SUM(toplam_kullanim_T2) AS TotalUsageValue, 'T2' AS UsageType FROM TblSayacOkumalari GROUP BY CONVERT(NVARCHAR,