Jun 2, 2011 · A compound key is a key whereby any part of the key is a foreign key. Example: in an a hotel reservation system, a reservation has the compound key, (GuestId, HotelId, ArrivalDate). GuestId identifies a Guest, and references the Guests table. HotelId identifies a Hotel, and references the Hotels table. ArrivalDate identifies a Date.

Mar 12, 2017 · A compound key does the same thing, but is composed of more than one field. So if you were a bit new and keyed your table of employees by Surname and FirstName, that would be the super key, and it would be a compound key, because its more than one field.

public class MyTable { [Key, Column(Order = 0)] public string SomeId { get; set; } [Key, Column(Order = 1)] public int OtherId { get; set; } } You can also look at this SO question. If you want official documentation, I would recommend looking at the official EF website.

Apr 9, 2009 · Primary key fields should be declared as not null (this is non standard as the definition of a primary key is that it must be unique and not null). But below is a good practice for all multi-column primary keys in any DBMS. create table foo ( fooint integer not null ,foobar string not null ,fooval real ,primary key (fooint, foobar) ) ;

May 21, 2010 · If the key is part of the class then use KeyedCollection. It is a Dictionary where the key is derived from the object. Under the covers it is Dictionary Don't have to repeat the key in the Key and Value. Why take a chance the key is not the same in the Key as the Value. Don't have to duplicate the same information in memory. KeyedCollection Class

May 13, 2022 · Just for clarification: a table can have at most one primary key. A primary key consists of one or more columns (from that table). If a primary key consists of two or more columns it is called a composite primary key. It is defined as follows: CREATE TABLE voting ( QuestionID NUMERIC, MemberID NUMERIC, PRIMARY KEY (QuestionID, MemberID) );

Jul 28, 2012 · If your objects contain the two strings used as key and it makes sense to define object equality based on the two, then define equals and hashCode in accordance and use the object as both key and value.

How to consider one key among composite primary keys in a table as a foreign key in a another table in postgres 1 Creating a unique composite key, where one of its components is a foreign key

Mar 17, 2014 · The columns to the right of MatchID do have a functional dependency on the (compound) primary key, as long as they represent that player's statistics in one particular match. If those columns instead represent the players overall statistics, then they're dependent only on PlayerID, and this design is not in 2NF.

Oct 20, 2010 · Another option would convert enum and int to some unique key. string key = String.Format("{0}/{1}", enumValue, intValue) That approach requires string parsing, a lot of extra work.