The quick answer
Create a Case saved search, check Public, and on the Available Filters subtab add Item as the first filter. Then go to Customization > Forms > Sublists, open the Item subtab, and add a line with that search, a Label, the record Tab to put it on, and the item types that should show it. Save. Each item record now has a subtab that runs the search for that item, so it lists only the cases whose Item field is the item you're looking at.
The screenshots show sample data. Person and company names are fictional. Use your own items, cases, and search names when following the steps.
Before you start
This example uses Kestrel Field Instruments. Its support team logs cases against four inventory items, and each case names its product in the Item field. There are 8 cases in all, and 3 of them name the HX-440 pressure transmitter. The goal is a subtab on HX-440, and on every other item, that lists that item's cases.
A custom sublist is a saved search shown as a subtab on a record. NetSuite ties the search to the record through the search's first available filter, which must be a list/record field. For a Case search on item records, that filter is Item.
You need support cases turned on and a role that can create saved searches and edit Custom Sublists. The Administrator role can. People who view the subtab also need permission to see cases. Only the case's Item field counts: a case that mentions the product only in its subject or message won't match.
01. Check the case and the item
Open CASE-1044 Reading drifts after calibration. Under Incident Information, the Item field is HX-440. That field is what ties a case to a product.
Now open item HX-440 and click the Communication tab. It has Activities, User Notes, and Files, and nothing that lists the item's cases.
02. Build the case search
Go to Lists > Search > Saved Searches > New and click Case. In Search Title, replace the default with Support Cases by Item. Check Public so the search can be picked for a sublist and other roles can see it. Sharing it through Audience works too.
Available as Sublist View is a different option. You don't need it for a custom sublist.
Leave Criteria empty so the search covers every case. On Results, click the Grab row and click Remove. A Grab link is no use on an item. The other default columns stay, and they'll be the sublist's columns.
On Available Filters, choose Item in Filter and click Add. This is the filter NetSuite fills with the item being viewed. It needs no value, and it doesn't have to show in the filter region. It does have to be first in the list.
03. Run the search on its own
Click Save & Run. The results show Total: 8, every case in the account, CASE-1041 to CASE-1048, across all four items. Nothing is filtered yet. The Item filter only narrows the results when the search runs as a sublist on an item.
04. Add the custom sublist
Go to Customization > Forms > Sublists and click the Item subtab. The page has a subtab for each kind of record the sublist can go on: Transaction, Entity, Item, and CRM. An item sublist goes on Item.
On the new line, choose Support Cases by Item in Search, type Support Cases by Item in Label, and choose Communication in Tab. Label is the subtab caption on the record. Tab is the record tab it sits under.
Check every item type box (Inventory Item, Non-inventory Item, Service, Expense Item, Other Charge, Group, Kit/Package, and Assembly/Bill of Materials) so every kind of item shows the subtab. An item type left unchecked doesn't get it. Click Add.
Click Save.
05. See the cases on the item
Open HX-440 again and click Communication. Open the item fresh; a page that was already open doesn't pick up the change. A new subtab, Support Cases by Item, now follows Files. Click it.
Check the result
- The subtab is labelled Support Cases by Item and sits on the Communication tab.
- It lists 3 cases: CASE-1041, CASE-1044, and CASE-1047, the ones whose Item is HX-440.
- The columns are the search's Results columns, without Grab.
Click Display shows no signal. CASE-1047 opens for Pinecrest Dairy Co-op, and its Item field is HX-440.
Because the search has no criteria, closed cases show too; CASE-1041 is Closed. To narrow it, add a criterion on the search such as Status, none of, Closed. To change the columns, edit the search's Results; the sublist has no column setup of its own.
Common questions
Why doesn't my saved search show up in the Custom Sublists Search list?
Check two things. The search needs a first available filter that's a list/record field, and it has to be shared, either with Public checked or through Audience. Available as Sublist View is a separate option and doesn't put the search in this list.
Why does my custom sublist show every record instead of only the current record's?
The first available filter isn't the one that points at the record. NetSuite matches on the first filter only, so if it's missing, or it's a different field than the one that names the record, there's nothing to tie the results to. For a case sublist on items, make Item the first available filter.
Which available filter does a custom sublist use?
Only the first one on the search's Available Filters subtab. It needs no value and doesn't have to show in the filter region. If you add other filters, move the record field back to the top.
Can I add the same kind of sublist to customers or transactions?
Yes. Customization > Forms > Sublists also has Transaction, Entity, and CRM subtabs. Build a search whose first available filter points at that kind of record, for example Customer on a sales order search for a customer's open orders.
How do I change the columns in the sublist?
Edit the saved search's Results subtab. The sublist shows exactly those columns, in that order, and there's no column setup on the Custom Sublists page.
Why don't I see the new subtab on my item?
Check that the item's type is checked on the sublist line and that you're looking on the tab you chose in Tab. Then reload the item. A page that was already open when you saved doesn't pick up the new subtab.