Refactor template lookup to eliminate duplication and improve type safety

Changes:
- Added MailingService.renderTemplateDocument() method to render from template document
- Created renderTemplateWithId() helper that combines lookup and rendering in one operation
- Updated sendEmail() to use renderTemplateWithId() instead of separate lookup and render
- Added runtime validation to ensure template collection exists before querying
- Eliminated duplicate template lookup (previously looked up twice per email send)

Benefits:
- Improved performance by reducing database queries from 2 to 1 per template-based email
- Better error messages when template collection is misconfigured
- Runtime validation complements TypeScript type assertions for safer code
- Cleaner separation of concerns in sendEmail() function

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/sendEmail.ts

@@ -1,5 +1,5 @@
 import { Payload } from 'payload'
-import { getMailing, renderTemplate, parseAndValidateEmails, sanitizeFromName } from './utils/helpers.js'
+import { getMailing, renderTemplateWithId, parseAndValidateEmails, sanitizeFromName } from './utils/helpers.js'
 import { BaseEmailDocument } from './types/index.js'
 import { processJobById } from './utils/emailProcessor.js'
 import { createContextLogger } from './utils/logger.js'
@@ -50,23 +50,8 @@ export const sendEmail = async <TEmail extends BaseEmailDocument = BaseEmailDocu
   let emailData: Partial<TEmail> = { ...options.data } as Partial<TEmail>
 
   if (options.template) {
-    // Find the template document to get its ID for the relationship field
-    const templatesCollection = mailingConfig.collections.templates || 'email-templates'
-    const { docs: templateDocs } = await payload.find({
-      collection: templatesCollection as any,
-      where: {
-        slug: {
-          equals: options.template.slug,
-        },
-      },
-      limit: 1,
-    })
-
-    if (!templateDocs || templateDocs.length === 0) {
-      throw new Error(`Template not found: ${options.template.slug}`)
-    }
-
-    const { html, text, subject } = await renderTemplate(
+    // Look up and render the template in a single operation to avoid duplicate lookups
+    const { html, text, subject, templateId } = await renderTemplateWithId(
       payload,
       options.template.slug,
       options.template.variables || {}
@@ -74,7 +59,7 @@ export const sendEmail = async <TEmail extends BaseEmailDocument = BaseEmailDocu
 
     emailData = {
       ...emailData,
-      template: templateDocs[0].id,
+      template: templateId,
       subject,
       html,
       text,

src/services/MailingService.ts

@@ -127,6 +127,17 @@ export class MailingService implements IMailingService {
       throw new Error(`Email template not found: ${templateSlug}`)
     }
 
+    return this.renderTemplateDocument(template, variables)
+  }
+
+  /**
+   * Render a template document (for when you already have the template loaded)
+   * This avoids duplicate template lookups
+   * @internal
+   */
+  async renderTemplateDocument(template: BaseEmailTemplateDocument, variables: TemplateVariables): Promise<{ html: string; text: string; subject: string }> {
+    this.ensureInitialized()
+
     const emailContent = await this.renderEmailTemplate(template, variables)
     const subject = await this.renderTemplateString(template.subject || '', variables)
 

src/utils/helpers.ts

@@ -130,6 +130,53 @@ export const renderTemplate = async (payload: Payload, templateSlug: string, var
   return mailing.service.renderTemplate(templateSlug, variables)
 }
 
+/**
+ * Render a template and return both rendered content and template ID
+ * This is used by sendEmail to avoid duplicate template lookups
+ * @internal
+ */
+export const renderTemplateWithId = async (
+  payload: Payload,
+  templateSlug: string,
+  variables: TemplateVariables
+): Promise<{ html: string; text: string; subject: string; templateId: PayloadID }> => {
+  const mailing = getMailing(payload)
+  const templatesCollection = mailing.config.collections?.templates || 'email-templates'
+
+  // Runtime validation: Ensure the collection exists in Payload
+  if (!payload.collections[templatesCollection]) {
+    throw new Error(
+      `Templates collection '${templatesCollection}' not found. ` +
+      `Available collections: ${Object.keys(payload.collections).join(', ')}`
+    )
+  }
+
+  // Look up the template document once
+  const { docs: templateDocs } = await payload.find({
+    collection: templatesCollection as any,
+    where: {
+      slug: {
+        equals: templateSlug,
+      },
+    },
+    limit: 1,
+  })
+
+  if (!templateDocs || templateDocs.length === 0) {
+    throw new Error(`Template not found: ${templateSlug}`)
+  }
+
+  const templateDoc = templateDocs[0]
+
+  // Render using the document directly to avoid duplicate lookup
+  const rendered = await mailing.service.renderTemplateDocument(templateDoc, variables)
+
+  return {
+    ...rendered,
+    templateId: templateDoc.id,
+  }
+}
+
 export const processEmails = async (payload: Payload): Promise<void> => {
   const mailing = getMailing(payload)
   return mailing.service.processEmails()