Junction tables in T-SQL

Question

In my database application, when I try to attach a page to a site, I get the following error:

System.InvalidOperationException: Can't perform Create, Update or Delete operations on 'Table(Junc_Page_Site)' because it has no primary key.

I intend a page to be able to be added to multiple sites - by using a junction table.

Below is the schema for the three tables in question (T-SQL). Any advice will be appreciated!

CREATE TABLE Site (
    Id     INTEGER    NOT NULL IDENTITY ,
    FkSiteId    INTEGER   ,
    Name     NVARCHAR(64)  NOT NULL ,
    Domain     NVARCHAR(128) ,
    Theme     NVARCHAR(32) ,
    ThemeVariation  NVARCHAR(32) ,
PRIMARY KEY(Id) ,
FOREIGN KEY(FkSiteId)
    REFERENCES    Site(Id));
GO



CREATE TABLE Page (
    Id      INTEGER    NOT NULL IDENTITY ,
    Title    NVARCHAR(64)  NOT NULL ,
    Description   NVARCHAR(256)  NOT NULL , 
    Keywords   NVARCHAR(1024)  NOT NULL ,
    ScriptName   NVARCHAR(64) , 
PRIMARY KEY(Id));
GO



CREATE TABLE Junc_Page_Site (
    FkPageId   INTEGER     NOT NULL ,
    FkSiteId   INTEGER    NOT NULL  ,
FOREIGN KEY(FkSiteId)
    REFERENCES Site(Id),
FOREIGN KEY(FkPageId)
    REFERENCES Page(Id));
GO

Answer 1

You're almost there. You just need to create what's called a "composite primary key", which is to say that you need to tell the database that the conbination of FkPageId and FkSiteId will be unique:

CREATE TABLE Junc_Page_Site (
    FkPageId INTEGER NOT NULL ,
    FkSiteId INTEGER NOT NULL  ,
FOREIGN KEY(FkSiteId)
    REFERENCES Site(Id),
FOREIGN KEY(FkPageId)
    REFERENCES Page(Id),
PRIMARY KEY (FkPageId, FkSiteId));