You still have to create the column checklist_id INTEGER before you add it as a Foreign key. So it would be: CREATE TABLE checklist ( _id INTEGER PRIMARY KEY AUTOINCREMENT, checklist_title TEXT, description TEXT, created_on INTEGER, modified_on INTEGER ); CREATE TABLE item ( _id INTEGER PRIMARY KEY AUTOINCREMENT, checklist_id INTEGER, item_text TEXT, item_hint TEXT, item_order … Read more
You may want to consider reading the Rails Guide on nested resources: http://guides.rubyonrails.org/routing.html#nested-resources In a nutshell: routes.rb resources :galleries do resources :pictures do end # Generates the routes: /galleries/:gallery_id/pictures pictures_controller.rb def new @gallery = Gallery.find(params[:gallery_id]) @picture = Picture.new end def create @gallery = Gallery.find(params[:gallery_id]) # gallery_id is passed in the URL @picture = @gallery.build(params[:picture]) if … Read more
Imagine a table that holds the TODOs of a team. If a TODO is not yet assigned to a member of the team, its user_id is NULL. If it is not NULL it is a foreign key to the users table.
If you review the foreign key documentation, if you have a relationship like Doc -> has many DocImages you need to define your foreign key on the DocImages class like so: class DocImage(models.Model): property = models.ForeignKey(Doc, related_name=”images”) If you don’t set related names, you can access the DocImages from the Doc like: Doc.docimage_set.all() Docs on … Read more
It is not supported to look beyond the current row in a CHECK constraint. http://www.postgresql.org/docs/9.1/interactive/sql-createtable.html says: A check constraint specified as a column constraint should reference that column’s value only, while an expression appearing in a table constraint can reference multiple columns. Currently, CHECK expressions cannot contain subqueries nor refer to variables other than columns … Read more
This is a bad design. Just make a 2-column primary key, and 2-column foreign keys to it. This is a fundamental anti-pattern called “encoding information in keys” which (thereby) are called “smart”, “intelligent” or “concatenated” keys. A good key is a “dumb” key. Eg:: Despite it now being easy to implement a Smart Key, it … Read more
Since Table2 has a composite primary key (FileID, FileType), then any reference to it must also include both columns. ALTER TABLE dbo.Table1 ADD CONSTRAINT FK_Table1_Table2 FOREIGN KEY(FileID, FileType) REFERENCES Table2(FileID, FileType) Unless you have a unique constraint/index on the Table2.FileID field (but if so: why isn’t this the PK??), you cannot create a FK relationship … Read more
You must make your foreign key nullable: public class User { public int Id { get; set; } public int? CountryId { get; set; } public virtual Country Country { get; set; } }
To achieve what you want you need to provide some aditional configuration.Code First convention can identify bidirectional relationships, but not when there are multiple bidirectional relationships between two entities.You can add configuration (using Data Annotations or the Fluent API) to present this information to the model builder. With Data Annotations, you’ll use an annotation called … Read more
None of that is necessary, especially not the doubling up the tables. That is pure insanity. Introduction Since the Standard for Modelling Relational Databases (IDEF1X) has been in common use for over 25 years (at least in the high quality, high performance end of the market), I use that terminology. Date & Darwen, despite1 consistent … Read more