foreign-keys

I have an entity Bar : @OneToMany(cascade = CascadeType.ALL, mappedBy = "bar") private Set<Foo> fooSet; And an entity Foo : @ManyToOne(optional = false) @JoinColumn(name = "bar_id") private Bar bar; Hibernate creates the foreign key constraint on foo.bar -> bar.id but it doesnt specify ON DELETE CASCADE . Why not? And is there any ways to achieve it? Alternatively I can add the ON DELETE CASCADE manually in the DB (and disable DDL generation), is this a good practice? And also, do I have to modify my code in some way to let Hibernate know that related records are deleted automatically by the

Possible Duplicate: Should I use foreign keys? Ok, let's assume we have two tables, users and comments . In comments we have a column comment_made_by_user_id and it means which user typed that particular comment. Why do we need to specify it as a foreign key? If we don't do that, it will still work. We specify primary keys, because it makes queries faster as far as I know (we need to search only for one row while when we don't have a primary key/index, we have to go through all rows). Is it just a good coding practise? When you use foreign keys you get: Data integrity faster queries. users:

I have the following two models: School and User, and a HABTM relationship between them, with a join table. In this join table, the foreign key refering to the User table is not called user_id but student_id . class School < ActiveRecord::Base has_and_belongs_to_many :students, :class_name => "User", :join_table => "schools_students", :foreign_key => "student_id" end class User < ActiveRecord::Base has_and_belongs_to_many :studying_schools, :class_name => "School", :join_table => "schools_students", :foreign_key => "school_id" end I would like to create in my Users and Schools fixtures a

I'm new to EF code first principal and currently with no clue what to do.. I have 2 POCO classes.. public class Problem { public int ProblemID { get; set; } public int UserID { get; set; } public int CategoryID { get; set; } public int RatingID { get; set; } public string Title { get; set; } public string Description { get; set; } public double Latitude { get; set; } public double Longitude { get; set; } public int State { get; set; } public DateTime CreatedOn { get; set; } public virtual Rating Rating { get; set; } public virtual Category Category { get; set; } public virtual User User { get;

I've just created my first mySQL table on my own (other than using Joomla, Wordpress, etc.) and I am MS SQL developer for years but normally I can easily create a foreign key in MS SQL but I came across a difficulty or lack of knowledge here. Here is my tables : users user_id int primary auto_increment username varchar(20) password varchar(20) posts post_id in primary auto_increment title varchar(100) message text user_id int When I try to add a foreign key to users which refers to posts->user_id , I cannot see the posts->user_id option in the option list Relation_view window on mySQL panel. I

Basically, I have a model where I've created a superclass that many other classes share, and then each of those classes has some unique features that differ from each other. Let's say class A is the superclass, and class B, C, and D are children of that class. Both class B and class C can have multiples of class D, however I've seen that it's best to put the foreign key relationship in class D, which then refers to its parent class. Now in other languages, I could simply say it has a ForeignKey relationship to class A, and then the language recognizes the classes' true type. However, I don't

I created database on my local machine. After moving my project to server I imported backup from local (because I had some important data there). Now,when I'm trying to update schema on my server it gives my this output: php app/console doctrine:schema:update --force Updating database schema... [Doctrine\DBAL\Exception\ForeignKeyConstraintViolationException] An exception occurred while executing 'ALTER TABLE golf_course ADD CONSTRAINT FK_EC96E162F1503E2B FOREIGN KEY (golf_id) REFERENCES golf (id)': SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a