title	Expressions (CEL)
description	Canonical CEL-based expression language for formulas, predicates, conditions, and dynamic seed values

Expressions

ObjectStack uses a single canonical expression language for every place a piece of metadata needs to compute a value or evaluate a condition:

Formula fields (type: 'formula')
Predicates — validation condition, sharing condition, field conditional rules (visibleWhen, readonlyWhen, requiredWhen), view section/column visibility (visibleWhen), action disabled, hook condition, flow decisions
Dynamic seed values — fixtures whose value depends on the install-time clock or identity context

The language is CEL (Google's Common Expression Language, Apache-2.0), evaluated through @objectstack/formula (thin wrapper over @marcbachmann/cel-js) plus the ObjectStack standard library.

Why CEL? Formal grammar, abundant public training corpus (so AI authors emit it natively), AST-first persistence, and sandboxed execution with bounded cost. ObjectStack does not ship a Salesforce-flavor DSL — the previous custom 22-function engine was deleted in M9. See the north-star principles on typed metadata over custom DSLs.

The `Expression` envelope

Every expression in metadata is persisted as the same envelope:

type Expression = {
  dialect: 'cel' | 'js' | 'cron' | 'template';
  source?: string;          // surface syntax
  ast?: unknown;            // parsed AST (filled by `objectstack compile`)
  meta?: { rationale?: string; generatedBy?: string };
};

ObjectStack ships four registered dialects (M9.9):

Dialect	Use for	Helper
`cel`	computed values, predicates, defaults, formulas	cel`...` / F`...` / P`...`
`cron`	recurring schedules (Job, ETL, sync, exports, jobs)	cron`...`
`template`	text interpolation (`{{path}}`) — notif/prompt/title	tmpl`...`
`js`	sandboxed L2 hook bodies (TypeScript source)	n/a

All dialects share the same variable scope (record, previous, os.user, os.org, os.env, vars for flow steps), so you author once and never have to relearn the syntax across surfaces.

**Predicates are bare CEL — never wrap field references in `{…}` braces.** The most common mistake (and the root cause of issue #1491) is a condition like `{record.rating} >= 4`: in CEL, `{…}` is a **map literal**, so it is a parse error. Write bare CEL: `record.rating >= 4`. Braces belong only in `{{ … }}` text templates. As of 7.6 a malformed expression no longer silently does nothing — it fails `objectstack build` and throws at runtime.

Template formatting (7.6). A template hole is a field path with an optional whitelisted formatter — {{ path | formatter[:arg] }} — with defined value→string semantics (no arbitrary logic; put logic in a CEL field):

tmpl`Deal {{record.name}} — {{record.amount | currency}} closes {{record.close_date | date:long}}`

Formatters: currency[:CODE], number[:decimals], percent[:decimals], date[:short|long|iso], datetime[:…], upper, lower, trim, truncate:N, default:'…', json. Single-brace {x} is not a valid template hole.

At input time you may write a bare string for shorthand — the spec transforms it into the right envelope based on the field type. The compiled artifact always contains the full envelope (and, after M9.2, the AST).

import { F, P, cel, cron, tmpl } from '@objectstack/spec';
import { ObjectSchema, Field } from '@objectstack/spec/data';

export const Invoice = ObjectSchema.create({
  name: 'invoice',
  nameField: 'display_title', // ADR-0079 — the record title is a designated field; composite titles migrate off the deprecated `titleFormat` to a text formula
  fields: {
    // Composite record title as a text formula, surfaced via `nameField` above.
    display_title: Field.formula({
      returnType: 'text',
      expression: F`"Invoice " + string(record.invoice_no) + " – " + record.customer.name`,
    }),
    total: Field.formula({
      returnType: 'number',
      expression: F`record.subtotal + record.subtotal * record.tax_rate`,
    }),
    po_number: Field.text({
      requiredWhen: P`record.amount > 10000`,
    }),
    // M9.9b — declarative default, evaluated at insert time
    issued_date: Field.date({
      defaultValue: cel`today()`,
    }),
  },
});

**A formula field's `type` is always `formula`** — that is the key the runtime evaluates (`objectql` computes a formula virtual field from its `expression` only). Do **not** pass `type: 'currency' | 'number' | …` to `Field.formula` — it is rejected by the typed `FieldInput` and, untyped, would override `type:'formula'` so the field silently never computes. To declare what the formula returns, set **`returnType`** (`'number' | 'text' | 'boolean' | 'date'`); it is inferred and stamped automatically by the AI build path, and consumers (dashboard measures, formatting) read it instead of re-parsing the expression. The CEL source is the **`expression`** key — it is the only key the schema and runtime read for a formula's source; there is no separate `formula` source key.

The three CEL tagged-template helpers — cel, F (formula alias), P (predicate alias) — are interchangeable; pick whichever reads best at the call site. cron and tmpl produce their respective envelopes.

CEL primer

CEL is documented at cel-spec. Cheat-sheet of what you'll write daily:

Concept	Syntax
Field on current record	`record.first_name`
Previous (in update hooks)	`previous.status`
Input to a hook	`input.amount`
Equality / inequality	`==` / `!=`
Logical	`&&` / `\|\|` / `!`
Ternary	`cond ? then : else`
String literal	`'single quotes'`
Membership	`record.region in ['us', 'eu']`
Field present	`has(record.foo)` (returns true even when value is `null`)

has() gotcha: has(record.x) is true whenever the key exists, even when its value is null. To check for "not blank" use isBlank(...) or record.x != null — see stdlib below.

ObjectStack CEL standard library

Registered automatically into every Environment by @objectstack/formula. All functions are pure given a pinned now, which is what makes objectstack build artifacts byte-stable across runs.

Function	Returns	Description
`now()`	timestamp	Pinned wall-clock at evaluation start
`today()`	timestamp	Calendar day in the business timezone, as UTC midnight
`daysFromNow(n)` / `daysAgo(n)`	timestamp	`today() ± n` days (calendar-day, not wall-clock)
`addDays(d, n)` / `addMonths(d, n)`	timestamp	Shift a given date; `addMonths` clamps to month end (Jan 31 + 1mo → Feb 28)
`date(s)` / `datetime(s)`	timestamp	Parse an ISO date / date-time string (aliases)
`daysBetween(a, b)`	int	Whole days from `a` to `b` (negative when `b` is earlier)
`isBlank(v)`	bool	True for `null`, `undefined`, `''`, `[]`
`isEmpty(v)`	bool	True for `null` or zero-length string/list/map
`coalesce(v, fallback)`	dyn	`v` when non-null, else `fallback`
`trim(v)`	string	`v` with leading/trailing whitespace removed
`joinNonEmpty(list, sep)`	string	`list` joined by `sep`, skipping blank entries
`upper(s)` / `lower(s)`	string	Case conversion
`contains(s, sub)` / `startsWith(s, p)` / `endsWith(s, p)`	bool	Substring checks (free-function form)
`matches(s, regex)`	bool	Regex test
`len(v)`	int	Length of a string / list / map (mirrors CEL's built-in `size()`)
`abs(x)` / `round(x)`	number	Numeric helpers
`min(a, b)` / `max(a, b)`	dyn	Smaller / larger operand (numeric comparison)

Add new helpers in packages/formula/src/stdlib.ts. Keep them pure, dependency-free, and AI-readable.

Variable scope

@objectstack/formula builds the scope per evaluation:

Binding	Source	Available in
`record`	the row being evaluated	formulas, validation, sharing, visibility
`previous`	row before update	hooks, validation on update
`input`	hook payload	hooks
`os.user`	install / request user	seed, predicates with identity
`os.org`	active organization	seed, predicates
`os.env`	install env (`prod`, `dev`, `test`)	seed, predicates

Build-time validation

objectstack build type-checks every expression against the object schema, so a mistake that would silently evaluate to null at runtime is caught before it ships. The same shared validator also runs when a flow is registered (registerFlow), so a flow authored dynamically gets the same verdict. Findings come at two severities: errors fail the build; warnings are advisory (surfaced, not fatal — promote them with --strict).

Check	Example	Severity
Qualify field references — a formula / validation / predicate binds only the `record` namespace, so a bare `amount` resolves to nothing and evaluates to `null`. Write `record.amount`.	`amount > 100` → `record.amount > 100`	error
Field must exist — a typo'd `record.<field>` is flagged with a did-you-mean.	`record.amont` → `record.amount`	error
Unknown function — a misspelled or nonexistent stdlib call.	`isBlnk(record.x)`	error
Type soundness — a text or boolean field used with an arithmetic (`+ - * / %`) or ordering (`< > <= >=`) operator against a number faults at runtime and evaluates to `null`. Store it as a number field, or drop the arithmetic.	`record.title * 2`	warning

Integer literals in arithmetic are fine. record.amount / 100, record.price * 2, record.total - fee all work — the engine handles mixed double × int arithmetic, so you never need the 100.0 / 2.0 float-literal workaround. Equality against any type is also safe (record.stage == 5 simply returns false), so only arithmetic/ordering on a genuinely text/boolean field is flagged.

In flow and automation conditions the record's fields are bound bare (stage == "won", not record.stage), so a bare reference is correct there. Instead, a bare identifier that is a near-miss of a real field gets a did-you-mean warning (a genuine flow variable is left alone), and the same type-soundness check applies.

Cookbook

Computed full name (handle nullable parts)

{
  name: 'full_name',
  type: 'formula',
  expression: F`joinNonEmpty([record.salutation, record.first_name, record.last_name], ' ')`,
}

joinNonEmpty skips blank parts, so you avoid the verbose triple-coalesce. Building the string by hand with + would also work, but CEL throws on null + string, so each nullable operand must be wrapped in coalesce(..., '').

Conditional formula

{
  name: 'roi',
  type: 'formula',
  expression: F`coalesce(record.actual_cost, 0) > 0
             ? ((coalesce(record.actual_revenue, 0) - record.actual_cost) * 100.0) / record.actual_cost
             : 0.0`,
}

Predicate (visibility, read-only, conditional required)

{
  name: 'rating',
  type: 'select',
  visibleWhen: P`record.status == 'qualified'`,
}

Field.text({
  visibleWhen: P`record.type == 'business'`,
  readonlyWhen: P`record.status == 'approved'`,
  requiredWhen: P`record.amount > 10000`,
})

Dynamic seed dates

Use CEL inside seed records to defer evaluation to install time. The SeedLoader pins a single now per load run, so the same dataset produces identical SHA-1 across builds while still being "fresh" relative to whoever installs the package.

import { defineSeed } from '@objectstack/spec/data';
import { cel } from '@objectstack/spec';
import { Opportunity } from './objects/opportunity.object';

export const opportunitySeed = defineSeed(Opportunity, {
  records: [
    {
      name: 'Acme Q3 Renewal',
      close_date: cel`daysFromNow(45)`,
      created_at: cel`now()`,
    },
  ],
});

Without CEL, new Date() would be evaluated at compile time — your package would ship with the timestamp from your laptop and every customer would see "stale" demo data. With CEL, the date resolves on the customer's clock at install time.

Validation rule

{
  name: 'amount_positive',
  type: 'script',
  condition: P`record.amount <= 0`,
  message: 'Amount must be positive.',
}

The generic CEL rule is type: 'script'. For script rules, the condition is the failure predicate — when it evaluates TRUE the validation fails, so invert the test (here amount <= 0 rejects non-positive amounts).

Hook condition

{
  name: 'notify_on_escalation',
  object: 'case',
  events: ['afterUpdate'],
  condition: P`previous.status != 'escalated' && record.status == 'escalated'`,
  body: { language: 'js', source: 'await ctx.notifyOpsTeam(record)' },
}

Formula patterns

Complex calculations and logic in formula fields.

Conditional Logic

Formula fields are CEL. Use ternary cond ? a : b for conditionals and &&/||/! for boolean logic. Reference fields via record.<field>:

// Tiered pricing
Field.formula({
  label: 'Discount Tier',
  returnType: 'text',
  expression: `
    record.amount > 1000000 ? "Platinum" :
    record.amount > 500000 ? "Gold" :
    record.amount > 100000 ? "Silver" : "Bronze"
  `,
})

// Status indicator
Field.formula({
  label: 'Health Score',
  returnType: 'text',
  expression: `
    record.is_active && record.days_since_contact < 30 ? "Healthy" :
    record.days_since_contact < 90 ? "At Risk" : "Critical"
  `,
})

Date Calculations

// Days until close
Field.formula({
  label: 'Days to Close',
  returnType: 'number',
  expression: 'daysBetween(record.close_date, today())',
})

// Contract end in 30 days
Field.formula({
  label: 'Expiring Soon',
  returnType: 'boolean',
  expression: 'record.status == "active" && daysBetween(record.end_date, today()) <= 30',
})

// Age in days
Field.formula({
  label: 'Age (Days)',
  returnType: 'number',
  expression: 'daysBetween(today(), record.created_date)',
})

Financial Calculations

// Gross margin (computes a number; a formula's type is always 'formula' —
// declare the value type with returnType, and decimal places with scale)
Field.formula({
  label: 'Gross Margin %',
  returnType: 'number',
  expression: 'record.revenue > 0 ? ((record.revenue - record.cost) / record.revenue) * 100 : 0',
  scale: 2,
})

// Weighted pipeline
Field.formula({
  label: 'Weighted Amount',
  returnType: 'number',
  expression: 'record.amount * (record.probability / 100)',
  scale: 2,
})

// Total with tax
Field.formula({
  label: 'Total with Tax',
  returnType: 'number',
  expression: 'record.subtotal * 1.0825', // 8.25% tax
  scale: 2,
})

Text Manipulation

// Uppercase
Field.formula({
  label: 'Code',
  returnType: 'text',
  expression: 'upper(record.sku)',
})

// Has a company email
Field.formula({
  label: 'Internal',
  returnType: 'boolean',
  expression: 'endsWith(lower(record.email), "@example.com")',
})

Lead scoring

// Formula: Lead score
Field.formula({
  label: 'Lead Score',
  returnType: 'number',
  expression: `
    (record.rating == "hot" ? 30 : record.rating == "warm" ? 20 : 10) +
    (record.annual_revenue > 1000000 ? 25 : 0) +
    (record.number_of_employees > 500 ? 20 : 0) +
    (record.industry in ["technology", "finance"] ? 15 : 0)
  `,
})

Best practices

✅ DO:

Keep formulas simple and readable
Add comments for complex logic
Test edge cases (null, zero, empty)
Use appropriate data types

❌ DON'T:

Create circular references
Use formulas for frequently changing data
Nest too many IF statements
Ignore null handling

Determinism contract

Two consecutive objectstack build runs with no source changes must produce byte-identical dist/objectstack.json. CEL plus pinned now is what makes this possible — there are zero compile-time-evaluated Date.now() calls in seed metadata. CI enforces this via SHA-1 comparison; if you add a new dialect or stdlib helper, ensure it preserves determinism.

Migration from the legacy formula DSL

The previous custom recursive-descent engine (packages/objectql/src/formula.ts, deleted in M9.5) had a Salesforce-style function set. Mechanical translation:

Legacy	CEL equivalent
`bare_field`	`record.bare_field`
`=` / `<>`	`==` / `!=`
`AND` / `OR` / `NOT`	`&&` / `\|\|` / `!`
`"text"`	`'text'` (single quotes preferred)
`IF(c, a, b)`	`c ? a : b`
`ISBLANK(x)`	`isBlank(record.x)`
`CONCAT(a, b, …)`	`a + b + …` (with `coalesce(...,'')`)
`TODAY()` / `NOW()`	`today()` / `now()`
`IN (a, b)`	`record.x in [a, b]`
`ISCHANGED(x)` (in update hook)	`previous.x != record.x`
`MONTH_DIFF(a, b)`	not yet — add to stdlib

Salesforce compatibility is not a project goal. Authors targeting Salesforce semantics rewrite their formulas in CEL.

Programmatic API

import { ExpressionEngine } from '@objectstack/formula';

// Compile + cache
const compiled = ExpressionEngine.compile({ dialect: 'cel', source: 'record.x * 2' });

// Evaluate
const result = ExpressionEngine.evaluate(
  { dialect: 'cel', source: 'record.x * 2' },
  { record: { x: 21 } },
);
// => { ok: true, value: 42 }

The low-level engine never throws — evaluate() returns { ok: false, error }. But call sites must not silently swallow that (ADR-0032): objectstack build fails on an invalid expression (with a located, schema-aware message), and at runtime the flow/rule engines throw a loud, attributed error instead of treating a bad expression as false/null. The same validateExpression validator backs objectstack build and metadata registration (and a planned validate_expression agent tool), so an expression is checked before it ships.

Field Metadata — declaring type: 'formula' fields
Seed Data — using cel\...`` for dynamic install-time values
Hook Bodies — when to use a JS hook vs a CEL condition
packages/formula/ — engine + stdlib source
North Star — architecture principles (typed metadata over custom DSLs)

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Expressions

The `Expression` envelope

CEL primer

ObjectStack CEL standard library

Variable scope

Build-time validation

Cookbook

Computed full name (handle nullable parts)

Conditional formula

Predicate (visibility, read-only, conditional required)

Dynamic seed dates

Validation rule

Hook condition

Formula patterns

Conditional Logic

Date Calculations

Financial Calculations

Text Manipulation

Lead scoring

Best practices

Determinism contract

Migration from the legacy formula DSL

Programmatic API

Related

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Expressions

The Expression envelope

CEL primer

ObjectStack CEL standard library

Variable scope

Build-time validation

Cookbook

Computed full name (handle nullable parts)

Conditional formula

Predicate (visibility, read-only, conditional required)

Dynamic seed dates

Validation rule

Hook condition

Formula patterns

Conditional Logic

Date Calculations

Financial Calculations

Text Manipulation

Lead scoring

Best practices

Determinism contract

Migration from the legacy formula DSL

Programmatic API

Related

The `Expression` envelope