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Now the core: a logic function that loads a template and a record, fills the placeholders, and saves a new document. We’ll write the business logic once as a handler, then expose it through several triggers. This chapter wires up two of them — an AI tool and a workflow action.

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The rendering helper

Keep pure logic in its own file so it’s easy to unit-test. This flattens a record into {{dot.path}} tokens and substitutes them. 
const PLACEHOLDER_PATTERN = /\{\{\s*([\w.]+)\s*\}\}/g;

export const renderTemplate = (body: string, values: Record<string, string>) => {
  const missingTokens = new Set<string>();
  const content = body.replace(PLACEHOLDER_PATTERN, (_m, token: string) => {
    const value = values[token];
    if (value === undefined || value === '') { missingTokens.add(token); return ''; }
    return value;
  });
  return { content, missingTokens: [...missingTokens] };
};
Because this file has no side effects, you can cover it with fast unit tests (yarn test:unit). See Testing.

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The handler

The handler uses the generated CoreApiClient to read and write CRM data. It loads the template, loads the target record, fills the body, and creates a document. 
import { CoreApiClient } from 'twenty-client-sdk/core';
import { loadRecordValues } from 'src/logic-functions/utils/load-record-values';
import { renderTemplate } from 'src/logic-functions/utils/render-template';

export const generateDocumentHandler = async (
  input: { templateId: string; recordId: string },
) => {
  const client = new CoreApiClient();

  // Use a filtered list query, not the singular lookup: the singular query
  // throws when nothing matches, which would become a 500 instead of a 404.
  const { documentTemplates } = await client.query({
    documentTemplates: {
      __args: { filter: { id: { eq: input.templateId } }, first: 1 },
      edges: { node: { id: true, name: true, body: true, target: true } },
    },
  });
  const documentTemplate = documentTemplates?.edges?.[0]?.node;
  if (!documentTemplate?.id) return { success: false, status: 404, message: 'Template not found.' };

  const record = await loadRecordValues(client, documentTemplate.target, input.recordId);
  if (!record.found) return { success: false, status: 404, message: 'Record not found.' };

  const { content, missingTokens } = renderTemplate(documentTemplate.body ?? '', record.values);

  const { createDocument } = await client.mutation({
    createDocument: {
      __args: { data: {
        name: `${documentTemplate.name} — ${record.displayName}`,
        content, status: 'GENERATED', templateId: documentTemplate.id,
      } },
      id: true, name: true,
    },
  });

  return { success: true, documentId: createDocument.id, content, missingTokens };
};
loadRecordValues runs a different query for a Person vs. a Company and flattens the result — see load-record-values.ts.

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Expose it as a tool and a workflow action

A single defineLogicFunction can carry several triggers. Here, toolTriggerSettings makes it callable by AI agents, and workflowActionTriggerSettings turns it into a step in the visual workflow builder. Both describe their input with a JSON schema. 
import { defineLogicFunction } from 'twenty-sdk/define';
import { jsonSchemaToInputSchema } from 'twenty-sdk/logic-function';
import { GENERATE_DOCUMENT_LOGIC_FUNCTION_UNIVERSAL_IDENTIFIER } from 'src/constants/universal-identifiers';
import { generateDocumentHandler } from 'src/logic-functions/handlers/generate-document-handler';
import { generateDocumentInputSchema } from 'src/logic-functions/schemas/generate-document-input.schema';

export default defineLogicFunction({
  universalIdentifier: GENERATE_DOCUMENT_LOGIC_FUNCTION_UNIVERSAL_IDENTIFIER,
  name: 'generate-document',
  description: 'Generate a document from a template and a CRM record.',
  timeoutSeconds: 30,
  toolTriggerSettings: {
    inputSchema: generateDocumentInputSchema,
  },
  workflowActionTriggerSettings: {
    label: 'Generate Document',
    icon: 'IconFileText',
    inputSchema: jsonSchemaToInputSchema(generateDocumentInputSchema),
    outputSchema: [{ type: 'object', properties: {
      success: { type: 'boolean' }, documentId: { type: 'string' },
    } }],
  },
  handler: generateDocumentHandler,
});
The input schema is a plain JSON schema describing templateId and recordId — see generate-document-input.schema.ts.

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Grant it access

Logic functions run as the app’s role. It needs to read templates and records and create documents, so allow that in src/roles/default-role.ts: 
export default defineApplicationRole({
  universalIdentifier: DEFAULT_ROLE_UNIVERSAL_IDENTIFIER,
  label: 'Document Generator default role',
  canReadAllObjectRecords: true,
  canUpdateAllObjectRecords: true,
  canAccessAllTools: true,
  canBeAssignedToAgents: true,
  permissionFlagUniversalIdentifiers: [SystemPermissionFlag.UPLOAD_FILE],
});
UPLOAD_FILE lets the function upload the generated PDF in the next section. See Roles for finer-grained permissions.

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Attach a real PDF file

A rendered text field is useful, but users want a real document. Let’s generate a PDF and store it on the record as a downloadable file. First, give the document object a FILES field to hold the PDF. Apps upload into their own files fields, so this field is what routes the upload: 
{
  universalIdentifier: DOCUMENT_FILE_FIELD_UNIVERSAL_IDENTIFIER,
  type: FieldType.FILES,
  name: 'file',
  label: 'File',
  icon: 'IconFileTypePdf',
  universalSettings: { maxNumberOfValues: 1 },
}
Now render that PDF. An app is a real Node project, so you can add any npm package you need and import it like anywhere else. We use pdf-lib to draw the PDF and marked to parse the Markdown body — the CLI installs them into the function’s runtime for you: 
yarn add pdf-lib marked
The full helper is generate-document-pdf.ts. It parses the Markdown into tokens with marked.lexer, then lays them out with pdf-lib: real headings, bold/italic runs, bullet and numbered lists, blockquotes and rules — a polished, multi-page A4 rendering of the template itself, rather than a wall of text.
A polished, marketable generated PDF
pdf-lib’s built-in fonts use WinAnsi encoding, so Western-European accents render out of the box; the helper maps smart quotes and dashes and drops characters it can’t encode. Rendering non-Latin scripts (Chinese, Arabic, Cyrillic) would mean embedding a Unicode font.
Then upload it and store the reference on the record. uploadFile routes bytes to your app-owned files field; the returned id is what you save: 
import { MetadataApiClient } from 'twenty-client-sdk/metadata';
import { generateDocumentPdf } from 'src/logic-functions/utils/generate-document-pdf';

const documentName = `${documentTemplate.name} — ${record.displayName}`;
const bytes = await generateDocumentPdf(documentName, content);
const fileName = 'proposal.pdf';

const uploaded = await new MetadataApiClient().uploadFile(
  Buffer.from(bytes),
  fileName,
  'application/pdf',
  DOCUMENT_FILE_FIELD_UNIVERSAL_IDENTIFIER,
);

await client.mutation({
  updateDocument: {
    __args: {
      id: documentId,
      data: { file: [{ fileId: uploaded.id, label: fileName }] },
    },
    id: true,
  },
});
The generated document now carries a downloadable PDF:
A document record with a generated PDF file
uploadFile only targets app-owned files fields (so uploads always require an app that owns the field, plus the UPLOAD_FILE role flag). That’s why the PDF lands on the record’s own file field — the same pattern the call-recorder app uses for recordings.
After this step: each generated document has a real, downloadable PDF. But nothing can call the generator from the UI yet — for that we need an HTTP route.

Next: HTTP routes →

Serve the function over HTTP and render documents as web pages.