foreign-keys

问题 I am little confused about my db design. I have orders table that may have records from one of many others. So is it OK to relate each tables with 1:1 to orders . Please look at orders domains and hostings table relations. My orders table rows has either a domain or hosting regarding to its orders_type value. 回答1: Are you asking if the orders should have 1:1 relationship with domains and another 1:1 relationship with hostings? If you are, the answer is no. Your hosting table has an orders_id

问题 I have two tables: Property (..., postcode_id, ...) Postcode (id, postcode, latitude, longitude) The relationship: class Property extends AppModel { public $belongsTo = array( 'Postcode' => array( 'className' => 'Postcode' ) ); class Postcode extends AppModel { public $hasMany = array( 'Property' => array( 'className' => 'Property' ) ); What I'd like to happen: Enter a postcode in the Property add form. Check entered postcode is in the Postcode table. If not, so some logic (possibly add it,

问题 I would like to make a system, which is photos belong to projects. I also enabled that I can upload a zipfile directly for a project and it will unzip and register the photos to the specified project. However, I am having troubles while defining the Photo class. I need to get the value of Project.file_zip.path with the current instance for defining img field's upload_to attribute. However, when I tried like below, it returns with AttributeError: 'ForeignKey' object has no attribute 'file_path

问题 I have a problem with NHibernate. What i am trying to to is very simple: I have two Classes. UserTicket and UserData. A UsertTicket has some UserData and a UserData belongs to one UserTicket: public class UserData{ public virtual int Id { get; set; } public virtual String PDF_Path { get; set; } } public class UserTicket { public virtual int Ticketnr { get; set; } public virtual IList<UserData> UserData { get; set; } } And here the mappig xml: <class name="UserTicket" table="UserTicket"> <id

问题 I am working on a Rails app with Sqlite and have a users table associated with several other tables. When trying to rename a column in Users, I'm getting the subject error when running rails db:migrate. I see a lot of posts here with similar issues, but none has worked. Specifically, the common remedy seems to be to use "dependent: :destroy" on all has_many and has_one associations. I am doing this but am still getting the error. What am I doing wrong? Below is my code: class User <

问题 What's the problem with this statement that gives me the following exception? s.addBatch("CREATE TABLE category ( id SMALLINT NOT NULL GENERATED ALWAYS AS IDENTITY \n" + "\t(START WITH 0, INCREMENT BY 1), title VARCHAR(100))\n" ); s.addBatch("CREATE TABLE task (id SMALLINT NOT NULL GENERATED ALWAYS AS IDENTITY \n" + "\t(START WITH 0, INCREMENT BY 1), title VARCHAR(100), cat_id INT, visible BOOLEAN, " + "deprecated BOOLEAN" + "CONSTRAINT fk_cat_id FOREIGN KEY (cat_id)\n" + "\tREFERENCES

问题 I'm trying to implement this constraint into my database: (In the table Race) CONSTRAINT (Date <= Meeting.EndDate) Essentially the column in the Race Table needs to be Less than the EndDate column in the Meeting table. Pretty sure I need to use a trigger to implement a foreign key however, I'm not that sure how I would go about implementing one. So Far, All I have is: CREATE OR REPLACE TRIGGER RaceDateCheck AFTER UPDATE OF Race ON StartDateCheck BEGIN INSERT INTO Race (MeetingEndDate) SELECT

问题 could someone explain me how to use foreign keys in hsql? I would like it in an create table, but working alter table is also ok. I am working without tools, just in eclipse whats wrong with the hsql code? CREATE TABLE user( t_id INTEGER GENERATED BY DEFAULT AS IDENTITY(START WITH 1, INCREMENT BY 1) PRIMARY KEY, name VARCHAR(30), lastname VARCHAR(30), email VARCHAR(30), --FOREIGN KEY (b_id) REFERENCES bookingnumber(b_id) ); CREATE TABLE bookingnumber ( b_id INTEGER PRIMARY KEY ); ALTER TABLE

问题 I know that you set a nullable key in your entity if you want that FK to be nullable: class ChildEntity { // Other properties not shown for brevity public int? ParentId { get; set; } public virtual ParentEntity Parent; { get; set; } } This will result in a nullable FK. It was suggested here that we should also set the optional relationship in Fluent: modelBuilder.Entity<ChildEntity>() .HasOptional(c => c.Parent) .WithMany() .HasForeignKey(c => c.ParentId); but this still doesn't set delete

问题 This is a 2 part question. Question 1: I am trying to create a foreign key on a table where I need to turn off the "Check Existing Data on Creation or Re-Enabling". I know theres an option visually but I'm looking for a way to do it programmatically. Is there anyway to do this? Question 2: I have a code table and two tables A and B that need to reference that code table. I want to have these both referenced from a relationship table but I want to able to use the same column. Can I have 2