From 5fb8c081f357091732f4d76f0bf95a8809fc397a Mon Sep 17 00:00:00 2001
From: Ariel Mashraki <mashraki@fb.com>
Date: Mon, 9 Sep 2019 01:18:52 -0700
Subject: [PATCH] ent/doc: add documentation and exmples to offline migrate

Summary: https://pxl.cl/Knr4

Reviewed By: alexsn

Differential Revision: D17253380

fbshipit-source-id: 517985f1b912c68e379da3412863b5d14927aedc
---
 doc/md/migrate.md | 71 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 70 insertions(+), 1 deletion(-)

diff --git a/doc/md/migrate.md b/doc/md/migrate.md
index e7d6f6c01..27adff220 100755
--- a/doc/md/migrate.md
+++ b/doc/md/migrate.md
@@ -112,4 +112,73 @@ func main() {
 and store this information in a table named `ent_types`. For example, type `A` will have the range
 of `[1,4294967296)` for its IDs, and type `B` will have the range of `[4294967296,8589934592)`, etc.
 
-Note that if this option is enabled, the maximum number of possible tables is **65535**. 
\ No newline at end of file
+Note that if this option is enabled, the maximum number of possible tables is **65535**. 
+
+## Offline Mode
+
+Offline mode allows you to write the schema changes to an `io.Writer` before executing them on the database.
+It's useful for verifying the SQL commands before they're executed on the database, or to get an SQL script
+to run manually. 
+
+**Print changes**
+```go
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+	
+	"<project>/ent"
+	"<project>/ent/migrate"
+	
+	"github.com/facebookincubator/ent/dialect/sql"
+)
+
+func main() {
+	db, err := sql.Open("mysql", "root:pass@tcp(localhost:3306)/test")
+	if err != nil {
+		log.Fatalf("failed connecting to mysql: %v", err)
+	}
+	ctx := context.Background()
+	client := ent.NewClient(ent.Driver(db))
+	// Dump migration changes to stdout.
+	if err := client.Schema.WriteTo(ctx, os.Stdout); err != nil {
+		log.Fatalf("failed printing schema changes: %v", err)
+	}
+}
+```
+
+**Write changes to file**
+```go
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+	
+	"<project>/ent"
+	"<project>/ent/migrate"
+	
+	"github.com/facebookincubator/ent/dialect/sql"
+)
+
+func main() {
+	db, err := sql.Open("mysql", "root:pass@tcp(localhost:3306)/test")
+	if err != nil {
+		log.Fatalf("failed connecting to mysql: %v", err)
+	}
+	ctx := context.Background()
+	client := ent.NewClient(ent.Driver(db))
+	// Dump migration changes to an SQL script.
+	f, err := os.Create("migrate.sql")
+	if err != nil {
+		log.Fatalf("create migrate file: %v", err)
+	}
+	defer f.Close()
+	if err := client.Schema.WriteTo(ctx, f); err != nil {
+		log.Fatalf("failed printing schema changes: %v", err)
+	}
+}
+```
\ No newline at end of file