gramlot.

Course · Lesson 03 of 20

Initialize structured Data

Use dataSetter and a clear Data path to give a page its initial values.

Reading · Practice2 sectionsPrerequisites: Read and compose Source
Course contents
Orientation
  1. 01 Install Gramlot and create Hello world
  2. 02 Connect text and colour to Data
  3. 03 Explore Data and Source with the inspector
  4. 04 Use relative and symbolic paths, then dataFormula
  5. 05 Call the server with dataRpc and .remote
Start a project
  1. 01 Create your first project
  2. 02 Read and compose Source
  3. 03 Initialize structured Data
  4. 04 Connect fields and values
Build a form
  1. 05 Accept values, preserve drafts
  2. 06 Declare a calculation
  3. 07 Run an action at the right time
  4. 08 Name behavior and understand lifecycle
Compose an interface
  1. 09 Arrange an application with containers
  2. 10 Style the page you own
  3. 11 Publish messages and ask before acting
  4. 12 Format values without changing Data
Connect services
  1. 13 Call an endpoint
  2. 14 Load a Source fragment
  3. 15 Load Data when it is read
  4. 16 Save, restore and send Data deliberately
Deliver your work
  1. 17 Organize pages and choose a host
  2. 18 Read the JavaScript edition
  3. 19 Deliver the JavaScript edition offline
  4. 20 Explain and change a complete form

A value has a location

A Data Bag holds values and node attributes. A literal path identifies a location. A leading dot resolves against the current datapath, so a customer branch can refer to .name without repeating the whole prefix.

The current declaration is dataSetter. Nested dictionaries become Bags recursively. It is initialization, not a persistence service, and a literal JSON string stays a string. The old data declaration is not an alias.

Python · excerpt inside main(root)
root.dataSetter("customer", {"name": "Ada", "city": "London"})
panel = root.div(datapath="customer")
panel.h2("^.name")
panel.p("^.city")

Read the first render carefully

Data setters for an inserted branch are installed before its DOM is built. A setter written after a visual declaration can therefore still supply the first displayed value. Multiple setters for the same path follow document order.

Keep calculated totals outside a collection you intend to sum. Otherwise the result can become one of its own inputs. Initial values, derived values and saved records have different jobs.

Your turn

Try it yourself

  1. Open Setters and defaults. Find a setter that appears after a control in Source.
  2. Reload and confirm that the control already shows the initialized value.
  3. Compare the Data path with the control’s default: identify which supplies the initial state.

Check your understanding

If a setter receives a JSON string, will it parse the string into a Bag?

Show the answer and expected result

No. A dictionary/object is converted recursively; a JSON string remains text. Parsing external input is a separate operation. Removing a setter declaration also does not delete the value it previously installed.

Working examples and reference