Configure File Reaction

The File Reaction Reaction A component that receives query result changes and takes action on them. Learn more writes query result changes Result Change Event A notification from a Continuous Query describing changes to its result set. Learn more to local or mounted filesystem paths. Each diff can be formatted with Handlebars templates and persisted with append, overwrite, or per-change behavior.

Basic Configuration

reactions:
  - kind: file
    id: output-diffs
    queries: [my-query]
    outputPath: /data/drasi-out
    writeMode: append

Configuration Reference

Write Modes

Handlebars Templates

Use templates to control the content written for each change type.

Per-Query Templates

reactions:
  - kind: file
    id: order-log
    queries: [orders-query]
    outputPath: /data/drasi-out
    writeMode: append
    filenameTemplate: "{{query_name}}.ndjson"
    routes:
      orders-query:
        added:
          template: '{"op":"add","order":{{json after}}}'
        updated:
          template: '{"op":"update","before":{{json before}},"after":{{json after}}}'
        deleted:
          template: '{"op":"delete","order":{{json before}}}'

Default Template

Apply a fallback template to all queries that don’t have a specific route:

reactions:
  - kind: file
    id: default-log
    queries: [query-a, query-b]
    outputPath: /data/output
    writeMode: append
    defaultTemplate:
      added:
        template: '{"op":"add","data":{{json after}}}'
      updated:
        template: '{"op":"update","before":{{json before}},"after":{{json after}}}'
      deleted:
        template: '{"op":"delete","data":{{json before}}}'

Raw JSON Fallback

When no templates are configured, each diff is serialized as a JSON object containing operation, query_name, timestamp, and the relevant data fields.

Template Variables

JSON Helper

Use {{json value}} to serialize any value as JSON:

defaultTemplate:
  added:
    template: '{"item":{{json after}}}'

Aggregation Diffs

Aggregation diffs use the updated template and populate before, after, and data (equivalent to after). The operation variable is set to "AGGREGATION".

Filename Templating

The filenameTemplate field supports Handlebars, including payload fields:

filenameTemplate: "item_{{after.id}}.json"

Filename Safety

Rendered filenames are sanitized before write. The following characters are replaced with _:

/ \ : * ? " < > | and null bytes

This allows payload-derived filenames while preventing invalid or unsafe file names.

Examples

NDJSON Append Log

Write all changes as newline-delimited JSON to a single file per query:

reactions:
  - kind: file
    id: ndjson-log
    queries: [orders, inventory]
    outputPath: /data/logs
    writeMode: append
    filenameTemplate: "{{query_name}}.ndjson"
    routes:
      orders:
        added:
          template: '{"event":"order_created","order":{{json after}}}'
        updated:
          template: '{"event":"order_updated","before":{{json before}},"after":{{json after}}}'
        deleted:
          template: '{"event":"order_cancelled","order":{{json before}}}'
      inventory:
        updated:
          template: '{"event":"stock_changed","sku":"{{after.sku}}","qty":{{after.quantity}}}'

Overwrite Latest State

Keep only the most recent state in a single file:

reactions:
  - kind: file
    id: latest-state
    queries: [dashboard-query]
    outputPath: /data/state
    writeMode: overwrite
    filenameTemplate: "dashboard.json"
    defaultTemplate:
      added:
        template: '{{json after}}'
      updated:
        template: '{{json after}}'

Per-Change Unique Files

Create a separate file for each change with a payload-derived filename:

reactions:
  - kind: file
    id: change-files
    queries: [events]
    outputPath: /data/events
    writeMode: per_change
    filenameTemplate: "{{query_name}}_{{operation}}_{{uuid}}.json"
    defaultTemplate:
      added:
        template: '{{json after}}'
      updated:
        template: '{"before":{{json before}},"after":{{json after}}}'
      deleted:
        template: '{{json before}}'

Payload-Derived Filenames

Use fields from the result data in filenames:

reactions:
  - kind: file
    id: item-files
    queries: [products]
    outputPath: /data/products
    writeMode: overwrite
    filenameTemplate: "product_{{after.id}}.json"
    defaultTemplate:
      added:
        template: '{{json after}}'
      updated:
        template: '{{json after}}'

Complete Example

host: 0.0.0.0
port: 8080
logLevel: info

sources:
  - kind: postgres
    id: orders-db
    host: ${DB_HOST}
    database: ecommerce
    user: ${DB_USER}
    password: ${DB_PASSWORD}
    tables:
      - public.orders

queries:
  - id: all-orders
    query: |
      MATCH (o:orders)
      RETURN o.id, o.customer, o.total, o.status
    sources:
      - sourceId: orders-db

reactions:
  - kind: file
    id: order-audit
    queries: [all-orders]
    outputPath: /data/audit
    writeMode: append
    filenameTemplate: "orders.ndjson"
    routes:
      all-orders:
        added:
          template: '{"ts":"{{timestamp}}","op":"add","id":"{{after.id}}","customer":"{{after.customer}}","total":{{after.total}}}'
        updated:
          template: '{"ts":"{{timestamp}}","op":"update","id":"{{after.id}}","status":"{{before.status}}->{{after.status}}"}'
        deleted:
          template: '{"ts":"{{timestamp}}","op":"delete","id":"{{before.id}}"}'

Documentation resources

Next steps

• Configure Log Reaction
• Configure HTTP Reaction
• Configure gRPC Reaction