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---
id: migrate
title: Database Migration
---
The migration support for `ent` provides the option for keeping the database schema
aligned with the schema objects defined in `ent/migrate/schema.go` under the root of your project.
## Auto Migration
Run the auto-migration logic in the initialization of the application:
```go
if err := client.Schema.Create(ctx); err != nil {
log.Fatalf("failed creating schema resources: %v", err)
}
```
`Create` creates all database resources needed for your `ent` project. By default, `Create` works
in an *"append-only"* mode; which means, it only creates new tables and indexes, appends columns to tables or
extends column types. For example, changing `int` to `bigint`.
What about dropping columns or indexes?
## Drop Resources
`WithDropIndex` and `WithDropColumn` are 2 options for dropping table columns and indexes.
```go
package main
import (
"context"
"log"
"<project>/ent"
"<project>/ent/migrate"
)
func main() {
client, err := ent.Open("mysql", "root:pass@tcp(localhost:3306)/test")
if err != nil {
log.Fatalf("failed connecting to mysql: %v", err)
}
defer client.Close()
ctx := context.Background()
// Run migration.
err = client.Schema.Create(
ctx,
migrate.WithDropIndex(true),
migrate.WithDropColumn(true),
)
if err != nil {
log.Fatalf("failed creating schema resources: %v", err)
}
}
```
In order to run the migration in debug mode (printing all SQL queries), run:
```go
err := client.Debug().Schema.Create(
ctx,
migrate.WithDropIndex(true),
migrate.WithDropColumn(true),
)
if err != nil {
log.Fatalf("failed creating schema resources: %v", err)
}
```
## Universal IDs
By default, SQL primary-keys start from 1 for each table; which means that multiple entities of different types
can share the same ID. Unlike AWS Neptune, where node IDs are UUIDs.
This does not work well if you work with [GraphQL](https://graphql.org/learn/schema/#scalar-types), which requires
the object ID to be unique.
To enable the Universal-IDs support for your project, pass the `WithGlobalUniqueID` option to the migration.
```go
package main
import (
"context"
"log"
"<project>/ent"
"<project>/ent/migrate"
)
func main() {
client, err := ent.Open("mysql", "root:pass@tcp(localhost:3306)/test")
if err != nil {
log.Fatalf("failed connecting to mysql: %v", err)
}
defer client.Close()
ctx := context.Background()
// Run migration.
if err := client.Schema.Create(ctx, migrate.WithGlobalUniqueID(true)); err != nil {
log.Fatalf("failed creating schema resources: %v", err)
}
}
```
**How does it work?** `ent` migration allocates a 1<<32 range for the IDs of each entity (table),
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**.
## 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"
)
func main() {
client, err := ent.Open("mysql", "root:pass@tcp(localhost:3306)/test")
if err != nil {
log.Fatalf("failed connecting to mysql: %v", err)
}
defer client.Close()
ctx := context.Background()
// 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 a file**
```go
package main
import (
"context"
"log"
"os"
"<project>/ent"
"<project>/ent/migrate"
)
func main() {
client, err := ent.Open("mysql", "root:pass@tcp(localhost:3306)/test")
if err != nil {
log.Fatalf("failed connecting to mysql: %v", err)
}
defer client.Close()
ctx := context.Background()
// 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)
}
}
```
## Foreign Keys
By default, `ent` uses foreign-keys when defining relationships (edges) to enforce correctness and consistency on the
database side.
However, `ent` also provide an option to disable this functionality using the `WithForeignKeys` option.
You should note that setting this option to `false`, will tell the migration to not create foreign-keys in the
schema DDL and the edges validation and clearing must be handled manually by the developer.
We expect to provide a set of hooks for implementing the foreign-key constraints in the application level in the near future.
```go
package main
import (
"context"
"log"
"<project>/ent"
"<project>/ent/migrate"
)
func main() {
client, err := ent.Open("mysql", "root:pass@tcp(localhost:3306)/test")
if err != nil {
log.Fatalf("failed connecting to mysql: %v", err)
}
defer client.Close()
ctx := context.Background()
// Run migration.
err = client.Schema.Create(
ctx,
migrate.WithForeignKeys(false), // Disable foreign keys.
)
if err != nil {
log.Fatalf("failed creating schema resources: %v", err)
}
}
```
|
