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Relationship Patterns

Guide for modeling relationships between objects using lookup, master_detail, and junction patterns.

Relationship Types

Type Lifecycle Required Sharing Roll-ups Use Case
lookup Independent Optional by default Independent Supported via summary "Related to"
master_detail Coupled (cascade delete) Forced only under controlled_by_parent; else lint-warned Inherits parent Supported via summary "Owned by"
tree Self-reference Optional N/A Not available Hierarchical

When to Use lookup vs master_detail

Use lookup When:

  • Child record can exist independently
  • Parent deletion should only clear the FK (deleteBehavior: 'set_null', the default)
  • Relationship is optional
  • Example: task.assigned_to → user (task can exist without assignment)

Use master_detail When:

  • Child record is meaningless without parent
  • Parent deletion should cascade to children
  • Relationship is mandatory
  • Example: invoice_line_item.invoice_id → invoice (line items belong to invoice)

Patterns

One-to-Many: lookup

// Parent: Account
export default ObjectSchema.create({
  name: 'account',
  fields: {
    name: { type: 'text', required: true },
  }
});

// Child: Contact (independent lifecycle)
export default ObjectSchema.create({
  name: 'contact',
  fields: {
    first_name: { type: 'text', required: true },
    account_id: {
      type: 'lookup',
      reference: 'account',
      required: false,  // Contact can exist without account
    },
  }
});

One-to-Many: master_detail

// Parent: Invoice
export default ObjectSchema.create({
  name: 'invoice',
  fields: {
    invoice_number: { type: 'text', required: true },
    total: {
      type: 'summary',
      summaryOperations: {
        object: 'invoice_line_item',
        field: 'amount',
        function: 'sum',
      },
    },
  }
});

// Child: Line Item (owned by parent)
export default ObjectSchema.create({
  name: 'invoice_line_item',
  fields: {
    invoice_id: {
      type: 'master_detail',
      reference: 'invoice',
      deleteBehavior: 'cascade',  // Delete line items when invoice deleted
      required: true,
    },
    product: { type: 'text', required: true },
    amount: { type: 'currency', required: true },
  }
});

Many-to-Many: Junction Object

// Side A: Project
export default ObjectSchema.create({
  name: 'project',
  fields: {
    name: { type: 'text', required: true },
  }
});

// Side B: Employee
export default ObjectSchema.create({
  name: 'employee',
  fields: {
    name: { type: 'text', required: true },
  }
});

// Junction: Project Assignment
export default ObjectSchema.create({
  name: 'project_assignment',
  fields: {
    project_id: {
      type: 'lookup',
      reference: 'project',
      required: true,
    },
    employee_id: {
      type: 'lookup',
      reference: 'employee',
      required: true,
    },
    role: { type: 'text' },
    hours_allocated: { type: 'number' },
  },
  indexes: [
    // One assignment per (project, employee) pair.
    { fields: ['project_id', 'employee_id'], unique: 'organization' },
  ],
});

Hierarchical: tree (Self-Reference)

export default ObjectSchema.create({
  name: 'category',
  fields: {
    name: { type: 'text', required: true },
    parent_category: {
      type: 'tree',
      reference: 'category',  // Self-reference
      required: false,
    },
  }
});

Delete Behaviors

Configure deleteBehavior on master_detail — cascade or restrict only; an authored set_null is refused at publish (it would orphan the detail row).

Behavior Effect Use Case
cascade Delete all child records Invoice → Line Items
restrict Prevent parent deletion if children exist Department → Employees 
{
  type: 'master_detail',
  reference: 'parent_object',
  deleteBehavior: 'cascade',  // or 'restrict' — 'set_null' is refused here
}

Roll-up Summaries

A parent summary field aggregates a child collection. The engine recomputes it server-side whenever a child is inserted/updated/deleted (inside the same transaction as the write, so it's consistent and never summed on the client).

// On the PARENT object:
{
  type: 'summary',
  summaryOperations: {
    object: 'invoice_line',        // child object to aggregate
    field: 'amount',               // child field to aggregate (ignored for count)
    function: 'sum',               // 'count' | 'sum' | 'min' | 'max' | 'avg'
    // relationshipField: 'invoice' // optional; auto-detected from the child's
                                     // master_detail/lookup field referencing
                                     // this parent when omitted
    // filter: { status: 'received' } // optional; only children matching this
                                       // `where` predicate are aggregated
  },
}

Empty collections roll up to 0 for count/sum, null for min/max/avg. Pairs naturally with inline editing (below): the parent total updates atomically as line items are saved.

Add filter (a query where FilterCondition) to aggregate only a subset of the children — this is how a single child object feeds several different totals. For example one engagement child yields total_signups (filter: { type: 'signup' }) and total_clicks (filter: { type: 'click' }), and a procurement_receipt child yields received_amount (function: 'sum', filter: { status: 'received' }). The predicate is ANDed with the parent-FK match; a child moving in or out of it (e.g. a status change) recomputes the parent on its next write like any other child update. Operator and compound forms work too (filter: { type: { $in: ['signup','trial'] } }).

Inline Editing (Master-Detail Entry)

Declare inline editing on the relationship, in the data model — not in a form view. Set inlineEdit: true on the child's master_detail (or lookup) field that points back to the parent. The parent's standard create/edit form then renders an editable grid for these children and saves parent + children in one atomic transaction — with no form-view config and no bespoke page. The UI is derived from metadata (relationship FK + child fields → grid columns).

// On the CHILD object's FK field:
export default ObjectSchema.create({
  name: 'invoice_line',
  fields: {
    invoice: {
      type: 'master_detail',
      reference: 'invoice',
      inlineEdit: true,            // ← edited inline within the Invoice form
      inlineTitle: 'Line Items',   // optional grid title
      // inlineColumns / inlineAmountField — optional overrides; columns are
      // otherwise derived from this object's fields.
    },
    quantity: { type: 'number' },
    amount:   { type: 'currency' },
  },
});

Set inlineEdit only for true line-item / composition children (invoice lines, order items, expense lines) — the things a user enters together with the parent. Leave it off for associations (comments, attachments, activity, audit): those are also master_detail (cascade delete) but should NOT clutter the parent's entry form — surface them as related lists on the detail page.

A form view may still set subforms to override the derived columns/order, but the relationship inlineEdit is the primary, zero-config path. See the objectstack-ui skill (Master-Detail Forms) for the rendering side.

Inline-edit form factor (grid vs form)

inlineEdit also picks how the children are entered:

inlineEdit: true       // auto — pick grid/form from the child's shape (default)
inlineEdit: 'grid'     // editable line-item grid (fast bulk entry; thin children)
inlineEdit: 'form'     // read-only list; "Add" / per-row edit opens the FULL form
  • 'grid' — spreadsheet-like editable grid. Best for thin line items (invoice/order lines): few columns, high volume, keyboard-fast.
  • 'form' — compact read-only list; Add / per-row edit opens the child's complete form. Best for fat children (long text, attachments, many fields) that don't fit a narrow grid cell.
  • true / omitted — smart default: picks form when the child has rich/form-only fields (textarea, file, image, json, location…) or more than ~8 editable fields, else grid. Set the string to override.

Modeling a 'grid' line item for the full editor. The grid lights up extra behaviors purely from how you model the child + parent (no UI config — details in the objectstack-ui skill → Master-Detail Forms):

// Parent
Invoice = {
  fields: {
    tax_rate: Field.number({ label: 'Tax Rate (%)' }),          // → live Subtotal/Tax/Total stack
    total: Field.summary({ summaryOperations: {                  // server roll-up of the line subtotal
      object: 'invoice_line', field: 'amount', function: 'sum' } }),
  },
}
// Child line
InvoiceLine = {
  fields: {
    invoice:  Field.masterDetail('invoice', { inlineEdit: 'grid' }),
    position: Field.number({ defaultValue: 0 }),                 // → drag-reorder, persisted (auto-hidden col)
    product:  Field.lookup('product', { required: true }),       // → catalog typeahead
    description: Field.text(),                                    // ← auto-filled from product.description
    quantity: Field.number({ required: true, defaultValue: 1 }),
    unit_price: Field.currency(),                                // ← auto-filled from product.unit_price
    amount:   Field.currency({ expression: 'record.quantity * record.unit_price' }), // computed, read-only, live
  },
}
  • Computed column — a stored currency/number field with an expression renders read-only and recomputes live in the grid, then persists. Keep it stored (NOT a formula field) so the parent summary can roll it up; the server only treats type: 'formula' as computed, so on a stored field the expression is a client compute hint and the sent value is stored verbatim.
  • Catalog auto-fill — a lookup line field + sibling columns whose names match fields on the referenced record (e.g. unit_price, description) → picking a record fills those cells.
  • Sort field — a numeric position / sort_order / sequence field is auto-detected, hidden from the grid, and stamped on drag-reorder.

Detail-page related lists (the read-side mirror)

Where inlineEdit is the write side (child pulled into the parent's entry form), the related list on the parent's record detail page is the read side. You usually don't declare it: every child relationship (master_detail and lookup) is shown as a related list on the parent's detail page by default — owned (master_detail) children first. The relationship flags exist to refine that:

// On the CHILD object's FK field:
project: {
  type: 'master_detail',
  reference: 'project',
  inlineEdit: true,                 // write side: edit inline in the Project form
  relatedList: 'primary',           // read side: promote to its OWN detail-page tab
  relatedListTitle: 'Tasks',        // title of the detail-page list
  relatedListColumns: ['title', 'status', 'priority', 'due_date'],
},

// Suppress a noisy association from the detail page entirely:
audit_ref: { type: 'master_detail', reference: 'invoice', relatedList: false },

relatedList is tri-state — a prominence hint, not a layout switch (ADR-0085):

  • 'primary' — CORE relationship: the detail page gives it its own tab. Every non-primary related list stacks under a single shared Related tab, so 'primary' is the one-word way to promote a child table to a first-class tab without a custom page.
  • false — suppress this child from the parent's detail page (chatty association/log children you don't want surfaced).
  • true / omitted — shown in the shared Related tab.

relatedListTitle / relatedListColumns override the derived title / columns; both are optional — when omitted, columns auto-derive from the child object's highlightFields (the same source the lookup picker uses). Audit FKs (created_by/updated_by/owner_id) never become related lists. A child that references the parent through several FKs (e.g. primary_account + partner_account) yields one related list per FK; a self-referential FK (a hierarchy) surfaces a "children" list. See the objectstack-ui skill for the rendering side.

Incorrect vs Correct

❌ Incorrect — Using lookup When master_detail is Needed

// Invoice line items should NOT be independent
export default ObjectSchema.create({
  name: 'invoice_line_item',
  fields: {
    invoice_id: {
      type: 'lookup',  // ❌ Child can exist without parent — wrong!
      reference: 'invoice',
    },
  }
});

✅ Correct — Using master_detail for Owned Children

export default ObjectSchema.create({
  name: 'invoice_line_item',
  fields: {
    invoice_id: {
      type: 'master_detail',  // ✅ Child owned by parent
      reference: 'invoice',
      deleteBehavior: 'cascade',
      required: true,
    },
  }
});

❌ Incorrect — Native Many-to-Many

// ObjectStack does not have native many-to-many type
{
  type: 'many_to_many',  // ❌ Not a valid field type
  reference: 'tag',
}

✅ Correct — Junction Object Pattern

// Create explicit junction object with two lookup fields
export default ObjectSchema.create({
  name: 'post_tag',
  fields: {
    post_id: { type: 'lookup', reference: 'post', required: true },
    tag_id: { type: 'lookup', reference: 'tag', required: true },
  },
});