尝试在FK T-SQL上将记录插入表错误

Question

I'm trying to insert new text book records into aa database. I have a Course table with columns ID (PK), CourseID , CourseTitle .

textBook table (all columns, ID (PK)) is a many to many relationship so multiple courses can have the same book and courses can also have multiple different books.

When I try to insert a new text book into my database using C# I get an error on my foreign key. The Course table is parent, Textbook table is child. The ID column in both tables is set to identity and auto increments. ID is my foreign key in my textBook table referencing the Course table.

here is my intermediate table.

CREATE TABLE [dbo].[BookCourse]
(
[cID] INT NOT NULL Unique, 
[BookID] INT NOT NULL Unique, 
[BookCourseID] INT NOT NULL, 
CONSTRAINT [PK_BookCourse] PRIMARY KEY ([BookCourseID]) 
)

here is my textBook table

CREATE TABLE [dbo].[textBooks] (
[thirteenISBN]   VARCHAR (255) NOT NULL,
[CourseID]       VARCHAR (50)  NOT NULL,
[BookTitle]      VARCHAR (255) NULL,
[Ancillary]      VARCHAR (255) NULL,
[BookActive]     VARCHAR (20)  NULL,
[ActiveDate]     VARCHAR (50)  NULL,
[InactiveDate]   VARCHAR (50)  NULL,
[Author]         VARCHAR (255) NULL,
[Imprint]        VARCHAR (100) NULL,
[Publisher]      VARCHAR (100) NULL,
[EditionAndDate] VARCHAR (120) NULL,
[tenISBN]        VARCHAR (255) NULL,
[VendorISBN]     INT           NULL,
[ebookAvailable] VARCHAR (50)  NULL,
[eISBN]          VARCHAR (255) NULL,
[Notes]          VARCHAR (255) NULL,
[BookID]             INT           IDENTITY (1, 1) NOT NULL,
CONSTRAINT [PK_textBooks] PRIMARY KEY CLUSTERED ([BookID] ASC), 
CONSTRAINT [FK_textBooks_ToTable] FOREIGN KEY ([BookID]) REFERENCES [BookCourse]([BookID])
);

Here is my Course Table

CREATE TABLE [dbo].[Course] (
[CourseID]    VARCHAR (50)  NOT NULL,
[CourseTitle] VARCHAR (255) NULL,
[cID]          INT           IDENTITY (1, 1) NOT NULL,
CONSTRAINT [PK_Course] PRIMARY KEY CLUSTERED ([cID] ASC), 
CONSTRAINT [FK_Course_ToTable] FOREIGN KEY ([cID]) REFERENCES [BookCourse]([cID]) 
);

Table Adapters with Insert:

JUTDMSTableAdapters.textBooksTableAdapter bookTableAdapter;
bookTableAdapter = new JUTDMSTableAdapters.textBooksTableAdapter();

JUTDMSTableAdapters.CourseTableAdapter courseTableAdapter;
courseTableAdapter = new JUTDMSTableAdapters.CourseTableAdapter();

courseTableAdapter.Insert( CourseID: txtCourseID.Text, CourseTitle: txtCourseTitle.Text);

bookTableAdapter.Insert( thirteenISBN: txt13ISBN.Text, CourseID: txtCourseID.Text, BookTitle: txtBookTitle.Text, Ancillary: txtAncillary.Text,
            BookActive: txtBookActive.Text, ActiveDate: txtActiveDate.Text, InactiveDate: txtInactiveDate.Text, Author: txtAuthor.Text,
            Imprint: txtImprint.Text, Publisher: txtPublisher.Text, EditionAndDate: txtEditionDate.Text,
            VendorISBN: vendISBN, tenISBN: txt10ISBN.Text, ebookAvailable: txtEBookAvailable.Text, eISBN: txtEISBN.Text, Notes: txtNotes.Text);

I figured in my Course table adapter insert I wouldn't have to add the cID column seeing as it is auto increment but I get this error:

Additional information: The INSERT statement conflicted with the FOREIGN KEY constraint "FK_Course_ToTable". The conflict occurred in database "F:\\HUTDMS V-2.0\\HUTDMS V-2.0\\APP_DATA\\HUTDMS.MDF", table "dbo.BookCourse", column 'cID'.

BookID in the textbook table is autoincrement cID in the Course table is autoincrement BookCourseID in the BookCourse table is autoincrement.

Answer 1

For many-to-many relationship you need to use three tables, Book table, Course table and then intermediate table - BookCourse table. Book table refers BookCourse, Course Table refers BookCourse. There are NOT direct references between Book and Course tables

You first add book into Book table, then Course into Course table, finally you add the pair (CourseID, BookID) into BookCourse table.

As for BookCourse table, you may add composite primary key (CourseID, BookID), or add identity key BookCourseID, but if latter then you need to make sure there are no duplicates - you can create an unique constraint.

https://en.wikipedia.org/wiki/Many-to-many_(data_model)