Interpolates variables in template strings.

Replaces {{variable}} placeholders with actual values from event data.

Examples

Basic interpolation:

iex> interpolate("Order #{{id}}", %{order: %{id: 123}}, :order)
"Order #123"

Nested attributes (preloaded relationships):

iex> interpolate("Hello {{user.name}}", %{order: %{user: %{name: "Alice"}}}, :order)
"Hello Alice"

Flattened keys (user.name becomes user_name):

iex> interpolate("Hello {{user_name}}", %{order: %{user: %{name: "Alice"}}}, :order)
"Hello Alice"

Missing values become empty string:

iex> interpolate("Value: {{missing}}", %{order: %{}}, :order)
"Value: "

Variable Syntax

Variables use double curly braces: {{variable_name}}

Direct attributes:

• {{id}} → resource.id
• {{status}} → resource.status
• {{total}} → resource.total

Nested attributes (dot notation):

• {{user.name}} → resource.user.name
• {{user.email}} → resource.user.email
• {{organization.name}} → resource.organization.name

Flattened keys (underscore notation):

• {{user_name}} → resource.user.name
• {{user_email}} → resource.user.email
• {{organization_name}} → resource.organization.name

Resource Key

The resource_key parameter specifies which key in the data map contains the main resource record:

data = %{order: %Order{id: 123}, user: %User{name: "Alice"}}

interpolate("Order {{id}}", data, :order)
# Uses data.order for variable lookup

Preloading

For nested attributes to work, relationships must be preloaded:

dispatch do
  event :created,
    load: [:user, :organization],  # Preload relationships
    content: [
      notification_message: "{{user_name}} created order in {{organization_name}}"
    ]
end

Type Conversion

Values are converted to strings:

• Atoms: :active → "active"
• Numbers: 123 → "123"
• Booleans: true → "true"
• DateTime: ~U[2025-01-01 10:00:00Z] → "2025-01-01 10:00:00Z"
• Nil: nil → "" (empty string)

Safety

• Missing variables become empty strings (no errors)
• Nil values become empty strings
• Handles missing relationships gracefully
• Does not execute code (just string replacement)