foreign-key-relationship

问题 I have the following tables in a relational database: [Sensor] LocationId [PK / FK -> Location] SensorNo [PK] [AnalogSensor] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] UpperLimit LowerLimit [SwitchSensor] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] OnTimeLimit [Reading] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] ReadingDtm [PK] [ReadingSwitch] LocationId [PK/FK -> Reading] SensorNo [PK/FK -> Reading] ReadingDtm [PK/FK -> Reading] Switch [ReadingValue]

问题 I have set up a table that contains a column with a foreign key, set to ON DELETE CASCADE (delete child when parent is deleted) What would the SQL command be to change this to ON DELETE RESTRICT ? (can't delete parent if it has children) 回答1: Old question but adding answer so that one can get help Its two step process: Suppose, a table1 has a foreign key with column name fk_table2_id , with constraint name fk_name and table2 is referred table with key t2 ( something like below in my diagram )

问题 I have set up a table that contains a column with a foreign key, set to ON DELETE CASCADE (delete child when parent is deleted) What would the SQL command be to change this to ON DELETE RESTRICT ? (can't delete parent if it has children) 回答1: Old question but adding answer so that one can get help Its two step process: Suppose, a table1 has a foreign key with column name fk_table2_id , with constraint name fk_name and table2 is referred table with key t2 ( something like below in my diagram )

问题 public class Foo { public string FooId{get;set;} public Boo Boo{get;set;} } public class Boo { public string BooId{get;set;} public Foo Foo{get;set;} } I was trying to do this in Entity Framework when I got the error: Unable to determine the principal end of an association between the types 'ConsoleApplication5.Boo' and 'ConsoleApplication5.Foo'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations. I have seen

问题 In a school system I have 2 tables, one called Staff which holds records of all member of staff for a school, teachers, admin, cooks and cleaners etc. Then I have a second table called Course with a foreign key relating to Staff to state who is the Course leader, now I only want to allow teachers to be the Course Leader, i.e. a cook can't be, but am not sure how to restrict this on the database level. Note : I asked a more complicated wrong question here - Oracle Unique Constraint - Trigger

问题 I am working on a project where there are several types of users (students and teachers). Currently to store the user's information, two tables are used. The users table stores the information that all users have in common. The teachers table stores information that only teachers have with a foreign key relating it to the users table. users table id name email 34 other fields teachers table id user_id subject 17 other fields In the rest of the database, there are no references to teachers.id

问题 this is my DB structure. this is the script I used to create the tables use for_stkoverflow; CREATE TABLE UserGroup ( groupid MEDIUMINT NOT NULL AUTO_INCREMENT, groupname VARCHAR(100), PRIMARY KEY (`groupid`) ); CREATE TABLE User_det ( Usrid MEDIUMINT NOT NULL AUTO_INCREMENT, usrname VARCHAR(255), groupid MEDIUMINT, PRIMARY KEY (`Usrid`), Foreign Key (groupid) references UserGroup (groupid) ); CREATE TABLE Accounts ( acid MEDIUMINT NOT NULL AUTO_INCREMENT, groupid MEDIUMINT, acname VARCHAR

问题 I know a lot of people is asking about one-to-one relationships on EF 4.1 but I can't seem to find an answer for this problem. I have these POCO classes: public class Contact { public decimal nCont_id { get; set; } public virtual WebsiteMembership WebsiteMembership { get; set; } //a bunch of other properties } public class WebsiteMembership { public int WebsiteMembershipId { get; set; } public virtual Contact Contact { get; set; } } Website membership's primary key (WebsiteMembershipId) is

问题 I've got a django app, where I'd like to define a relationship between two classes at a base level. It also makes sense to me to define the relationship between the children of those base classes - so that I get something like this: class BaseSummary(models.Model): base_types... class BaseDetail(models.Model): base_detail_types... base_summary = models.ForeignKey('BaseSummary') class ChildSummary(BaseSummary): child_summary_types... class ChildDetail(BaseDetail): child_detail_type... child

问题 Is there a way to prevent Doctrine from assigning a contraint on both sides of a one-to-one relationship? Ive tried moving the definition from one side to the other and using owning side but it still places a constraint on both tables. when I only want the parent table to have a constraint - ie. its possible for the parent to not have an associated child. For example iwant the following sql schema essentially: CREATE TABLE `parent_table` ( `child_id` varchar(50) NOT NULL, `id` integer