add to FAQ how to use custom types

README.md

@@ -216,6 +216,77 @@ The provider supports the following databases:
  ).Load(&Models.Address{}, &Models.Person{})
  ```
 
+* **How to handle enums and custom types?** -
+ The recommended way to handle custom types that are not supported by GORM such as postgres enums is to use [composite schemas](https://atlasgo.io/atlas-schema/projects#data-source-composite_schema). 
+
+ First you need to define your custom type inside state file, lets call it `schema.sql`:
+ ```sql
+ CREATE TYPE "status" AS ENUM ('active', 'inactive', 'deleted');
+ ```
+
+ Next, you need to add the custom type to your GORM model using [type field tag](https://gorm.io/docs/models.html#Fields-Tags): 
+ ```diff filename ="models/player.go"
+ package models
+
+ import (
+ "gorm.io/gorm"
+ )
+
+ type Player struct {
+ gorm.Model
+ ID int `gorm:"primaryKey"`
+ + Status string `gorm:"type:status"`
+ }
+
+ ```
+ Next, you need to use schema composed of your GORM schema and `schema.sql` file, you can do it by using the next `atlas.hcl` config file:
+
+ ```hcl
+ data "external_schema" "gorm" {
+ program = [
+ "go",
+ "run",
+ "-mod=mod",
+ "ariga.io/atlas-provider-gorm",
+ "load",
+ "--path", "./models",
+ "--dialect", "postgres",
+ ]
+ }
+
+ data "composite_schema" "app" {
+ schema "public" {
+ url = "file://schema.sql"
+ }
+ schema "public" {
+ url = data.external_schema.gorm.url
+ }
+ }
+
+ env "composed" {
+ src = data.composite_schema.app.url
+ dev = "docker://postgres/15/dev?search_path=public"
+ migration {
+ dir = "file://migrations"
+ }
+ format {
+ migrate {
+ diff = "{{ sql . \" \" }}"
+ }
+ }
+ }
+
+ ```
+ Now, when running: `atlas migrate diff --env composed` new migration file should be created, containing the custom enum type:
+
+ ```sql filename ="20240623142238.sql"
+ -- Create enum type "status"
+ CREATE TYPE "status" AS ENUM ('active', 'inactive', 'deleted');
+ -- Modify "players" table
+ ALTER TABLE "players" ADD COLUMN "status" "status" NULL;
+ ```
+
+
 ### License
 
 This project is licensed under the [Apache License 2.0](LICENSE).