foreign-keys

I have two related clases JPA-annotated. Alarm and Status. One Alarm can have one Status. What I need is to be able to delete one Status and "propagate" a null value to the Alarms that are in that Status that has been deleted. That is, I need the foreign key to be defined as " on delete set null ". @Entity public class Alarm { @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="sequence") @SequenceGenerator(name="sequence", sequenceName="alarm_pk_seq") private Integer id; @OneToOne(cascade=CascadeType.ALL) @JoinColumn(name="idStatus") private Status status; // get/set } @Entity

Given a model with ForeignKeyField (FKF) or ManyToManyField (MTMF) fields with a foreignkey to 'self' how can I prevent self (recursive) selection within the Django Admin (admin). In short, it should be possible to prevent self (recursive) selection of a model instance in the admin. This applies when editing existing instances of a model, not creating new instances. For example, take the following model for an article in a news app; class Article(models.Model): title = models.CharField(max_length=100) slug = models.SlugField() related_articles = models.ManyToManyField('self') If there are 3

If I define tables a and b as follows: CREATE TABLE a(i integer); ALTER TABLE a ADD CONSTRAINT pkey_a PRIMARY KEY (i); CREATE TABLE b(j integer); ALTER TABLE b add CONSTRAINT fkey_ij FOREIGN KEY (j) REFERENCES a (i) MATCH SIMPLE ON UPDATE CASCADE ON DELETE CASCADE; INSERT INTO a(i) VALUES(1); And then do the following: START TRANSACTION; SET CONSTRAINTS ALL DEFERRED; INSERT INTO b(j) VALUES(2); INSERT INTO a(i) VALUES(2); COMMIT; It produces the error below. Why is SET CONSTRAINTS not having the desired effect? ERROR: insert or update on table "b" violates foreign key constraint "fkey_ij" SQL

In SQLite, foreign key constraints are disabled by default . What's the best way to configure Laravel 5.1's SQLite database connection to enable foreign key constraints? I don't see a way of doing this in ['connections']['sqlite'] in /config/database.php . Here's one solution. In the boot() method of App\Providers\AppServiceProvider , add: if (DB::connection() instanceof \Illuminate\Database\SQLiteConnection) { DB::statement(DB::raw('PRAGMA foreign_keys=1')); } Thanks to @RobertTrzebinski for this blog post regarding Laravel 4. For me using a the facade DB within App\Providers

I am creating a class which, takes a table from a database, and displays it to a web-page, with as much functionality as possible. One of the things I would like to support, would be having the class detect which columns in the table have a foreign key constraint on them, so that it can then go to those tables, get all of their values and use them in a select-box which is called when you edit those fields, to avoid someone violating foreign key constraints, The main problem is discovering which fields have a foreign key constraint on them, and which tables they are pointing to. Does anyone

How can I get the foreign key values? I have a common vehicle model that links to the year, series, engine type, body style, transmission and drive train...all as foreign keys. I'd like to get the values of these fields for my app, but I'm stuck as to how I'd go about them. Any ideas will be highly appreciated. class Model(models.Model): model = models.CharField(max_length=15, blank=False) manufacturer = models.ForeignKey(Manufacturer) date_added = models.DateField() def __unicode__(self): name = ''+str(self.manufacturer)+" "+str(self.model) return name class Year(models.Model): ALPHA_NUMERIC