Resolver

Resolvers are custom GraphQL endpoints with business logic that execute on the Tailor Platform.

Overview

Resolvers provide:

• Custom GraphQL queries and mutations
• Type-safe input/output schemas
• Access to TailorDB via Kysely query builder
• User context for authentication/authorization

Comparison with Tailor Platform Pipeline Resolver

The SDK's Resolver is a simplified version of Tailor Platform's Pipeline Resolver.

Pipeline Resolver	SDK Resolver
Multiple steps with different operations	Single body function
Declarative step configuration	Imperative TypeScript code
Built-in TailorDB/GraphQL steps	Direct database access via Kysely
CEL expressions for data transformation	Native TypeScript transformations

Example Comparison

Pipeline Resolver (Tailor Platform native):

steps:
  - name: getUser
    operation: tailordb.query
    params:
      type: User
      filter:
        email: { eq: "{{ input.email }}" }
  - name: updateAge
    operation: tailordb.mutation
    params:
      type: User
      id: "{{ steps.getUser.id }}"
      input:
        age: "{{ steps.getUser.age + 1 }}"

Resolver (SDK):

createResolver({
  name: "incrementUserAge",
  operation: "mutation",
  input: { email: t.string() },
  body: async (context) => {
    const db = getDB("tailordb");
    const user = await db
      .selectFrom("User")
      .selectAll()
      .where("email", "=", context.input.email)
      .executeTakeFirstOrThrow();

    await db
      .updateTable("User")
      .set({ age: user.age + 1 })
      .where("id", "=", user.id)
      .execute();

    return { oldAge: user.age, newAge: user.age + 1 };
  },
  output: t.object({ oldAge: t.int(), newAge: t.int() }),
});

Creating a Resolver

Define resolvers in files matching glob patterns specified in tailor.config.ts.

Definition Rules:

• One resolver per file: Each file must contain exactly one resolver definition
• Export method: Must use export default
• Uniqueness: Resolver names must be unique per namespace

import { createResolver, t } from "@tailor-platform/sdk";

export default createResolver({
  name: "add",
  operation: "query",
  input: {
    left: t.int(),
    right: t.int(),
  },
  body: (context) => {
    return {
      result: context.input.left + context.input.right,
    };
  },
  output: t.object({
    result: t.int(),
  }),
});

Input/Output Schemas

Define input/output schemas using methods of t object. Basic usage and supported field types are the same as TailorDB. TailorDB-specific options (e.g., index, relation) are not supported.

You can reuse fields defined with db object, but note that unsupported options will be ignored:

const user = db.type("User", {
  name: db.string().unique(),
  age: db.int(),
});

createResolver({
  input: {
    name: user.fields.name,
  },
});

Custom Type Name (typeName)

Enum and nested object fields in input/output schemas generate protobuf type names automatically (e.g., {ResolverName}{FieldName}). Use typeName() to set a custom name:

createResolver({
  name: "createOrder",
  operation: "mutation",
  input: {
    address: t
      .object({
        street: t.string(),
        city: t.string(),
        zip: t.string(),
      })
      .typeName("ShippingAddress"),
    status: t.enum(["pending", "confirmed", "shipped"]).typeName("OrderStatus"),
  },
  // ...
});

Constraints:

• Only available on enum() and object() fields — calling on scalar types is a compile error
• Cannot be called twice on the same field
• Can be chained with description()

This is useful when the same logical type appears in multiple resolvers or when you want a predictable, human-readable name in the generated GraphQL schema.

Warning: Do not set typeName to an existing TailorDB type name on an object() that contains enum or nested fields. Child fields without an explicit typeName auto-generate names using {parentTypeName}{FieldName}, which can collide with the TailorDB type's own enum/nested type names.

// Collision — "Item" + "status" auto-generates "ItemStatus",
//   which collides with the TailorDB Item type's status enum
output: t
  .object({
    id: t.uuid(),
    status: t.enum(["ACTIVE", "INACTIVE"]),
  })
  .typeName("Item"),

// OK — use a distinct name that won't collide
output: t
  .object({
    id: t.uuid(),
    status: t.enum(["ACTIVE", "INACTIVE"]),
  })
  .typeName("DeactivateItemOutput"),

// OK — explicitly set typeName on child enum too
output: t
  .object({
    id: t.uuid(),
    status: t.enum(["ACTIVE", "INACTIVE"]).typeName("DeactivateItemStatus"),
  })
  .typeName("Item"),

Input Validation

Add validation rules to input fields using the validate method:

createResolver({
  name: "createUser",
  operation: "mutation",
  input: {
    email: t
      .string()
      .validate(
        ({ value }) => value.includes("@"),
        [({ value }) => value.length <= 255, "Email must be 255 characters or less"],
      ),
    age: t.int().validate(({ value }) => value >= 0 && value <= 150),
  },
  body: (context) => {
    // Input is validated before body executes
    return { email: context.input.email };
  },
  output: t.object({ email: t.string() }),
});

Validation functions receive:

• value - The field value being validated
• data - The entire input object
• user - The user performing the operation

You can specify validation as:

• A function returning boolean (uses default error message)
• A tuple of [function, errorMessage] for custom error messages
• Multiple validators (pass multiple arguments to validate)

Validation runs automatically before the body function executes. When validation fails, individual errors are returned in the GraphQL errors array with field-level paths:

{
  "errors": [
    {
      "message": "Value must be non-negative",
      "path": ["createUser", "age"]
    }
  ]
}

Body Function

Define actual resolver logic in the body function. Function arguments include:

• input - Input data from GraphQL request
• user - The user who called this resolver; unaffected by authInvoker
• invoker - The principal running this function; equals user by default, or the machine user set by authInvoker. null for anonymous calls.
• env - Environment variables declared in tailor.config.ts

Using Kysely for Database Access

If you're generating Kysely types with a generator, you can use getDB to execute typed queries:

import { getDB } from "../generated/tailordb";

createResolver({
  name: "getUser",
  operation: "query",
  input: {
    name: t.string(),
  },
  body: async (context) => {
    const db = getDB("tailordb");
    const result = await db
      .selectFrom("User")
      .select("id")
      .where("name", "=", context.input.name)
      .limit(1)
      .executeTakeFirstOrThrow();
    return {
      result: result.id,
    };
  },
  output: t.object({
    result: t.uuid(),
  }),
});

Query vs Mutation

Use operation: "query" for read operations and operation: "mutation" for write operations:

// Query - for reading data
createResolver({
  name: "getUsers",
  operation: "query",
  // ...
});

// Mutation - for creating, updating, or deleting data
createResolver({
  name: "createUser",
  operation: "mutation",
  // ...
});

Event Publishing

Enable event publishing for a resolver to trigger executors on resolver execution:

createResolver({
  name: "processOrder",
  operation: "mutation",
  publishEvents: true,
  // ...
});

Behavior:

• When publishEvents: true, resolver execution events are published
• When not specified, it is automatically set to true if an executor uses this resolver with resolverExecutedTrigger
• When explicitly set to false while an executor uses this resolver, an error is thrown during tailor apply

Use cases:

1. Auto-detection (recommended): Don't set publishEvents - the SDK automatically enables it when needed by executors

   // publishEvents is automatically enabled because an executor uses this resolver
   export default createResolver({
     name: "processPayment",
     operation: "mutation",
     // publishEvents not set - auto-detected
     // ...
   });
   
   // In executor file:
   export default createExecutor({
     trigger: resolverExecutedTrigger("processPayment"),
     // ...
   });

2. Manual enable: Enable event publishing for external consumers or debugging

   createResolver({
     name: "auditAction",
     operation: "mutation",
     publishEvents: true, // Enable even without executor triggers
     // ...
   });

3. Explicit disable: Disable event publishing for a resolver that doesn't need it (error if executor uses it)

   createResolver({
     name: "internalHelper",
     operation: "query",
     publishEvents: false, // Explicitly disable
     // ...
   });

Authentication

Specify an authInvoker to execute the resolver with machine user credentials. Pass the machine user name as a plain string — it is type-narrowed to the names you defined in your auth config:

import { createResolver, t } from "@tailor-platform/sdk";

export default createResolver({
  name: "adminQuery",
  operation: "query",
  output: t.object({ result: t.string() }),
  body: async () => {
    // Executes as "batch-processor" machine user
    return { result: "ok" };
  },
  authInvoker: "batch-processor",
});

The machine user name is looked up in the auth service configured on your app (machineUsers in defineAuth). The namespace is resolved automatically — no need to import auth from tailor.config.ts in resolver files.

Deprecated: auth.invoker("batch-processor") still works, but is deprecated. Importing auth into runtime files pulls config-layer (Node-only) dependencies into the bundle.

Note: authInvoker controls the permissions for database operations and other platform actions. The user object passed to body still reflects the original caller, while invoker reflects the principal actually running the body.