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
;