foreign-keys

I have a production database where I have renamed several column's that are foreign keys. Obviously mysql makes this a real pain to do in my experience. My solution was to drop all the indexes and foreign keys, rename the id columns, and then re-add the indexes and foreign keys. This works great on mysql 5.1 on windows for the development database. I went to run my migration script on my debian server, which is also using mysql 5.1, and it gives the following error: mysql> ALTER TABLE `company_to_module` -> ADD CONSTRAINT `FK82977604FE40A062` FOREIGN KEY (`company_id`) REFERENCES `company` (

I have an sqlite database structured as follows: CREATE TABLE IF NOT EXISTS Patient ( PatientId INTEGER PRIMARY KEY AUTOINCREMENT ); CREATE TABLE IF NOT EXISTS Event ( PatientId INTEGER REFERENCES Patient( PatientId ), DateTime TEXT, EventTypeCode TEXT, PRIMARY KEY( PatientId, DateTime, EventTypeCode ) ); CREATE TABLE IF NOT EXISTS Reading ( PatientId INTEGER REFERENCES Patient( PatientId ), DateTime TEXT REFERENCES Event (DateTime), EventTypeCode TEXT REFERENCES Event (EventTypeCode), Value REAL, PRIMARY KEY( PatientId, DateTime, EventTypeCode ) ); I insert a Patient with Id #1 then I run:

As the result of a form post, I'm trying to save a new Brand record. In my view, Gender is a dropdown, returning an Integer, which is populated from ViewData("gender") I've setup my link as follows: gID = CInt(Request.Form("Gender")) Brand.GenderReference.EntityKey = New EntityKey("DB_ENTITIES.Gender", "Id", gID) TryUpdateModel(Brand) DB.SaveChanges() Which results in the following error. Entities in 'DB_ENTITIES.Brand' participate in the 'FK_Brand_Gender' relationship. 0 related 'Gender' were found. 1 'Gender' is expected. Could someone explain the parameters in plain english to me. I've also

My Order class has: public int CustomerId { get; set; } public Customer Customer { get; set; } Do I really need both properties to make a relation working? I am not using disconnected entities, I am using code first approach. Ying According to Julia Lerman's book: Programming Entity Framework: DbContext , the difference lies at the difficulty of updating the navigation property. In page 85, She suggests "If there is one thing you can do to make your life easier in N-Tier scenarios, it’s to expose foreign key properties for the relationships in your model." The book includes samples for both

I have problem with deleting related rows in Entity Framework 4.1. I have tables with relations Book 1<--->* BookFormats I have set the on delete cascade: ALTER TABLE [dbo].[BookFormats] WITH CHECK ADD CONSTRAINT [FK_BookFormats_Book] FOREIGN KEY([BookID]) REFERENCES [dbo].[Book] ([BookID]) on delete cascade The EDMX property Then, I want to remove the all BokFormats items related to my Book object: var originalBook = m.db.Book.First(x => x.BookID == bookId); originalBook.BookFormats.Clear(); m.db.SaveChanges(); But, I get the error: The operation failed: The relationship could not be changed

For example to create a hierarchy of categories you use a column 'parent_id', which points to another category in the same table. Should this be a foreign key? What would the dis/advantages be? Yes. Ensures that you don't have an orphan (entry with no parent), and depending on usage, if you define a cascading delete, when a parent is deleted, all its children will also be deleted. Disadvantage would be a slight performance hit just like any other foreign key. Yes, you should. If you have an attribute in a relation of database that serves as the primary key of another relation in the same

I was wondering, What will be my motivation to use constraint as foreign key in MySQL, as I am sure that I can rule the types that are added? Does it improve performance? Foreign keys enforce referential integrity . These constraints guarantee that a row in a table order_details with a field order_id referencing an orders table will never have an order_id value that doesn't exist in the orders table. Foreign keys aren't required to have a working relational database (in fact MySQL's default storage engine doesn't support FKs), but they are definitely essential to avoid broken relationships and