jx:dataValidation

jx:dataValidation adds Excel data validation rules to cells during template processing. Dropdowns, integer ranges, decimal constraints, date ranges, text length limits — configured right in the template, populated from your data.

Syntax

jx:dataValidation(lastCell="B1" type="list" formula1="choices" allowBlank="true")
jx:dataValidation(lastCell="C1" type="whole" operator="between" formula1="1" formula2="100")
jx:dataValidation(lastCell="D1" type="decimal" operator="greaterThan" formula1="0")

Attributes

Attribute	Required	Description
`lastCell`	Yes	Bottom-right cell of the validation area
`type`	Yes	Validation type: `list`, `whole`, `decimal`, `date`, `textLength`, `custom`
`formula1`	Yes	Primary constraint — for `list`, an expression resolving to a comma-separated string or slice; for numeric types, the min/value
`formula2`	No	Secondary constraint — the max value for `between`/`notBetween` operators
`operator`	No	Comparison: `between`, `notBetween`, `equal`, `notEqual`, `greaterThan`, `lessThan`, `greaterThanOrEqual`, `lessThanOrEqual`
`allowBlank`	No	Allow empty cells (default: `true`)
`showInputMessage`	No	Show tooltip when cell is selected (default: `false`)
`inputTitle`	No	Input message title
`inputMessage`	No	Input message body
`showErrorMessage`	No	Show error popup on invalid input (default: `false`)
`errorTitle`	No	Error popup title
`errorMessage`	No	Error popup message
`errorStyle`	No	Error style: `stop`, `warning`, `information` (default: `stop`)

When to use jx:dataValidation

Use it whenever your generated spreadsheet will be edited by humans after generation. Data validation prevents bad input at the source:

Dropdown lists for status fields, categories, or country codes
Integer constraints on quantity columns
Decimal ranges on price/discount fields
Date ranges on scheduling sheets
Text length limits on comment fields

The most common use case — a dropdown list populated from your data:

Cell B2 comment:
  jx:dataValidation(lastCell="B2" type="list" formula1="statusOptions" showInputMessage="true" inputTitle="Status" inputMessage="Pick a status")

data := map[string]any{
    "statusOptions": "Open,In Progress,Closed,Deferred",
}

When a user clicks cell B2 in the output, they get a dropdown with four choices and a helpful tooltip.

Example: Integer range

Constrain a quantity field to whole numbers between 1 and 1000:

Cell C2 comment:
  jx:dataValidation(lastCell="C2" type="whole" operator="between" formula1="1" formula2="1000" showErrorMessage="true" errorTitle="Invalid quantity" errorMessage="Enter a whole number between 1 and 1000" errorStyle="stop")

No Go code needed — the constraints are literals in the template. If a user types 0 or 1500, Excel blocks it with your custom error message.

Example: Decimal with minimum

Ensure a price field is always positive:

Cell D2 comment:
  jx:dataValidation(lastCell="D2" type="decimal" operator="greaterThan" formula1="0" showErrorMessage="true" errorTitle="Invalid price" errorMessage="Price must be greater than zero")

Inside loops

Combine with jx:each to apply validation to every generated row:

Cell A1 comment:
  jx:area(lastCell="D5")
  jx:each(items="items" var="item" lastCell="D1")

Cell B1 comment:
  jx:dataValidation(lastCell="B1" type="list" formula1="categories")

Every row gets the same dropdown. The validation rule is applied per-row during expansion.

Deferred execution

jx:dataValidation uses deferred execution — the validation rules are collected during template processing and applied in a single batch after all rows are written. This is both faster and ensures correct cell references even when rows shift during expansion.

Common pitfalls

List source must be a comma-separated string or a slice. formula1="Red,Green,Blue" works; so does a slice value in your data. Excel rejects spaces around commas — keep it tight.
Validation doesn’t block existing values. If the cell already has a value that violates the rule, Excel keeps it. Validation only fires on new user input.
Validation rules are dropped in streaming mode. Use sequential or auto mode if validations are critical.
Custom validations need an Excel formula, not a Go expression. type="custom" formula1 is an Excel formula (e.g. LEN(A1)<=10), evaluated by Excel — not by xlfill.

What’s next?

Add structured Excel tables with auto-filter and banded rows:

jx:table →