Adding Customer Specific Record in Master Table - sql-server

Question

I have the following table designed already.
Now the new requirement is i need to show some Category for all the
tenants. Also each tenant should able to add their new Category into
the Master Category. So they can see all master + their specific
categories
Tenant Table
TenantId
Name
Group Table
GroupId
Name
Category Table
CategoryId
Name
TenantXCategory
TenantId
CategoryId
What changes i can do in above tables to achieve it? I tried this below
Modified Category table to below.
Category Table
CategoryId
Name
TenantId NULL // This indicates tenant specific category
Add a unique key for TenantId and Name
Then queried
SELECT *
FROM Category where TenantId = 1
UNION
SELECT *
FROM Category where TenantId IS NULL
But the problem is if two tenant only want to see a particular
Category, I need to add a new row with other TenantId in Category
table. This mean i am creating duplicate entry in a lookup table. Any
suggestion to achieve the new requirement?

Answer 1

So, a tenant A may see:
(1) master categories,
(2) categories that belong to tenant A,
(3) categories which belong to another tenant and which the other tenant explicitly allowed tenant A to see
Your present schema seems to satisfy the requirements. In particular, the first two rules can indeed be implemented using a nullable TenantId column in the Category table, where NULL would stand for a master category and a non-NULL value would reference the creator/owner of the category and thus signify a tenant-specific category. (I might rename the column to something like OwnerTenantId for better clarity, but that might be just me.)
To retrieve only master categories or those that belong to the specified tenant, you could use the query you've posted in your question or this one (which will probably yield an identical execution plan to your query's):
SELECT
CategoryId,
CategoryName,
CASE
WHEN TenantId = #TenantId THEN 'Mine'
WHEN TenantId IS NULL THEN 'Master'
END AS Ownership
FROM Category
WHERE TenantId = #TenantId
OR TenantId IS NULL
;
To implement the third rule, you could use your TenantXCategory table to store categories available to tenants in addition to those that are accessible using the first two rules. That is, if tenant M permits tenant N to see some of tenant M's categories, the categories' Ids would be inserted into TenantXCategory along with tenant N's Id.
So, to query all categories available to a particular tenant, you could do something along the lines of the following:
SELECT
c.CategoryId,
c.CategoryName,
CASE
WHEN c.TenantId = #TenantId THEN 'Mine'
WHEN c.TenantId IS NULL THEN 'Master'
WHEN tc.CategoryId IS NOT NULL THEN 'Someone else''s'
END AS Ownership
FROM Category c
LEFT JOIN TenantXCategory tc
ON tc.CategoryId = c.CategoryId AND tc.TenandId = #TenantId
WHERE c.TenantId = #TenantId
OR c.TenantId IS NULL
OR tc.CategoryId IS NOT NULL
;

Answer 2

If you're going to be adding additional categories, you should probably have an identifier to distinguish between master and user-defined categories.
CREATE TABLE CategoryType (
[CategoryTypeID] int primary key identity,
[Description]
)
CREATE TABLE Category (
[CategoryID] int primary key identity,
[CategoryName] nvarchar(max)
[CategoryTypeID] int
)
/* CategoryTypes
1 Master
2 User-defined */
Show categories for a specific tenant
SELECT *
FROM TenantXCategory txc
JOIN Tenant t
ON t.TenantID = txc.TenantID
JOIN Category c
ON c.CategoryID = txc.CateoryID
WHERE t.TenantName = N'user1909604'
-- AND c.CategoryTypeID = 1 -- Only show master categories
-- AND c.CategoryTypeID = 2 -- Only show user-defined categories
-- AND c.CategoryID in (1, 2) -- Only show specific categories
To add a category for a user, store the category in your cross reference table. If the category doesn't exist, you'll have to add it to the category table first.
INSERT TenantXCategory (TenantID, CategoryID)
SELECT #TenantID, #CategoryID
--
Unless you're storing who created the category (for auditing purposes), this should work. If not, I misunderstood your question and you should clarify what you're trying to do.