Build a CRUD App with Node and DynamoDB, Part 3

Part 2 gave the page add and delete. This part makes the cells themselves editable, with each change patched to DynamoDB the moment it is committed and put back if the server refuses it. It also adds a full-screen button and moves the row form out of its drawer into a panel that is part of the page.

Source: the part-3 folder of toclocoinc/lattice-tutorial-crud-dynamodb (Code, Download ZIP). Needs Lattice Grid 1.76.0 or later.

Step 1: the function learns PATCH

On the function's Code tab, replace index.mjs with lambda/index.mjs from the download and choose Deploy.

PATCH takes ?sku= and a JSON body holding only the fields that changed. It builds a DynamoDB update expression from the fields it allows (name, category, quantity, price), stamps updated, and refuses to update a product that does not exist, so a PATCH can never create one by accident. It answers with the whole product as stored.

The allow-list matters. A PATCH endpoint is a public door in this tutorial, and without the list a caller could set any attribute on any product. With it, the function only ever changes the four fields the page edits.

Step 2: allow PATCH through the URL

Configuration, Function URL, Edit. Under the CORS settings add PATCH to Allow methods, keeping GET, POST and DELETE and the content-type header. Save. The IAM policy from part 2 already includes UpdateItem, so nothing changes there.

Step 3: the page

Paste your Function URL into web/index.html as before and open it.

Editable cells. Four columns now carry edit: true. Double-click a quantity, type a new number, press Enter. The cell shows the new value at once, and the grid calls the commit hook you gave it:

edit: {
  commit: (write) => api('PATCH', '?sku=' + encodeURIComponent(write.key), { [write.colId]: write.value }),
},

write names the row's key, the column and the new value, and the promise you return settles the write: resolve and the cell stays, reject and the grid puts the old value back and fires cell:reverted, which the status line reports. That is optimistic write-back: the user never waits for the network, and a refusal is visible rather than silent.

Try it against the rules: clear a name and press Enter. The function answers 400, the cell reverts, and the status line says why.

Full screen. The button calls grid.maximise.toggle(). The grid fills the window, remembering where it came from and its scroll position, and the same button or Escape puts it back. The grid's own rail offers the same action if you turn the tool panel on; a button is the shorter path for this page.

The form in a panel. The row form has two new lines:

rowForm: {
  container: '#form',
  trigger: false,
  ...
},

With a container, the form renders inside that element instead of over the grid as a drawer. trigger: false takes double-click away from the form, because the cells now want it; the menu gains an Edit in form item that calls grid.form.open(p.key) instead. Right-click a row, choose it, and the row appears in the side panel with the same fields as part 2's form. Save goes through the same commit hook as a cell edit, one call per changed field, so nothing about persistence changed when the form moved. Add product opens the same panel over an empty record, and create handles it as in part 2.

That double-click decision is worth making on purpose in any page that has both. Left to the defaults, the form opens on double-click and the cell never enters edit mode, which reads as "editing does not work".

Step 4: check the table

Change a price, then look at the item in Explore table items. The price and the updated date have moved. Change it again in the console instead and reload the page; the grid shows the console's value, because the page has no copy of the truth beyond what the function returns.

What you have

A grid that reads, adds, edits and deletes against your own table, with every change confirmed by the server and every refusal shown. The page is under a hundred lines of script, and the parts that would take a week to build by hand, the form, the menu, the optimistic edit with revert, the full-screen mode, came from the grid.

Where to go next

Two things this series left out on purpose. The Function URL has no authentication, so anyone with the URL can change your products; the next step for a real application is an authorizer in front of it, and the grid does not care which. And the function returns every product on every load, which is right at sixty rows and wrong at sixty thousand; the grid's pushdown sources move filtering, sorting and paging into the function so the browser only asks for what it shows. Both are covered in the guides.

Cleaning up

As in part 1: delete the function, the table and the role.

Read the full source, including lambda/index.mjs and web/index.html, on the public repository, or grab it as a ZIP download and skip the cloning.