SQL Junction Table

Good-day,

I am attempting to create a very simple database that uses a Junction Table. (see diagram)

Basically, what I would like to achieve is to assign one product to multiple categories;  When I run the code bellow, (in C#) I receive a constraint error;

I am wondering what  specifically is wrong with the diagram, and how I can change the DB to allow a product in multiple categories?

Thanks for your time
var adapterManager = new TableAdapterManager
            {
                ProductCategoryTableAdapter = new ProductCategoryTableAdapter(),
                CategoryTableAdapter = new CategoryTableAdapter(),
                ProductTableAdapter = new ProductTableAdapter()
            };
 
            adapterManager.UpdateAll(_dataSet);

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PastorDwayneAsked:
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Raja Jegan RConnect With a Mentor SQL Server DBA & ArchitectCommented:
Ok.. I hope your C# code is trying to insert same record twice or some thing like that because I tried the following and it works fine for me

create table category ( categoryid int identity primary key, subcategoryid int,
name varchar(50));
create table product ( productid int indentity primary key, name varchar(250), desc varchar(max));
create table productcategory ( productid int, categoryid int);

alter table productcategory add constrain pk_prodcat primary key ( productid, categoryid);

insert into category (subcategoryid , name )values ( 1, 'test');
insert into category (subcategoryid , name )values ( 2, 'abc');

insert into product ( name, desc) values ( 'abc','test');
insert into product ( name, desc) values ( 'cde','xyz');

insert into productcategory values ( 1,1);
insert into productcategory values ( 2,2);
insert into productcategory values ( 2,1);

update productcategory
set productid = 1,
      categoryid = 2
where productid = 2
and categoryid = 1

I have all valid scenarios as mentioned by you and is working fine.
Revert If I am wrong anywhere in my assumption
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madhuottapalamCommented:
If you are getting constraint error , you must be inserting child first and then Master table. Do master first and then child

Madhu
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Raja Jegan RSQL Server DBA & ArchitectCommented:
The INSERT order should be like Product, Category and ProductCategory or Category, Product and ProductCategory.

If you try to insert in ProductCategory before Product or Category you may receive a Constraint violation as its Product and Category ID's are not available in those tables.

Hope this helps
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PastorDwayneAuthor Commented:
Thanks for your comments;

How would I change the following code to produce this result?

Thanks again;
var adapterManager = new TableAdapterManager
            {
                ProductCategoryTableAdapter = new ProductCategoryTableAdapter(),
                CategoryTableAdapter = new CategoryTableAdapter(),
                ProductTableAdapter = new ProductTableAdapter()
            };
 
            adapterManager.UpdateAll(_dataSet);

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PastorDwayneAuthor Commented:
Also, the exact error I am getting is:

ConstraintException was unhandled
Column 'ProductID, CategoryID' is constrained to be unique.  Value '0, 2' is already present.
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Raja Jegan RSQL Server DBA & ArchitectCommented:
What are you trying to do is a Hierarchical update.
Try this one out.
var adapterManager = new TableAdapterManager
            {
                CategoryTableAdapter = new CategoryTableAdapter(),
                ProductTableAdapter = new ProductTableAdapter(),
                ProductCategoryTableAdapter = new ProductCategoryTableAdapter()
            };
 
            adapterManager.UpdateAll(_dataSet);

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Raja Jegan RSQL Server DBA & ArchitectCommented:
<< ConstraintException was unhandled
Column 'ProductID, CategoryID' is constrained to be unique.  Value '0, 2' is already present. >>

Then it means that you have values 0, 2 already in ProdcutCategory table and you are trying to update the same value 0, 2 for some other record.

Since you have ProductID and CategoryID combination as Primary Key or Unique Key combination you might obtain that error.
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PastorDwayneAuthor Commented:
Thanks rrjegan17, I removed the two primary keys from the junction table, and ordered the update as you have mentioned;  however now I receive this error:

The INSERT statement conflicted with the FOREIGN KEY constraint "FK_ProductCategory_Product". The conflict occurred in database "MyDB", table "dbo.Product", column 'ProductID'.
The statement has been terminated.

Why would this be?  Also, is it alright for a SQL table to have no primary keys?

Thanks for your time
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Raja Jegan RSQL Server DBA & ArchitectCommented:
<< The INSERT statement conflicted with the FOREIGN KEY constraint "FK_ProductCategory_Product". The conflict occurred in database "MyDB", table "dbo.Product", column 'ProductID'.
The statement has been terminated. >>

This means that you are trying to insert some records into ProductID column of ProductCategory table which is not present in the Product table. You have to first Insert some Products into Product table, some Categories into Category table and after that insert records into ProductCategory table to resolve this out.

<< I removed the two primary keys from the junction table >>

Does that mean deleted the records or removed the Primary keys itself. Have the Primary key constraint to ensure data integrity.
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PastorDwayneAuthor Commented:
Thanks rrjegan17;

I re-added the Primary keys to the junction table, and there are no records in any of the tables.
 
No I receive this error

ConstraintException was unhandled
Column 'ProductID, CategoryID' is constrained to be unique.  Value '0, 2' is already present.

upon executing the following code:
_dataSet.ProductCategory.AddProductCategoryRow(_itemsRow, _categoriesRow);

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PastorDwayneAuthor Commented:
Yes, that's exactly it;  It was trying to add duplicate records,

Thanks rrjegan17 very much for your help!
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Raja Jegan RSQL Server DBA & ArchitectCommented:
Welcome
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