Don't load in all drivers by default #40

Requires activating drivers with a _ style import, e.g.
import "_ github.com/mattes/migrate/driver/postgres"

README.md

@@ -78,6 +78,9 @@ See GoDoc here: http://godoc.org/github.com/mattes/migrate/migrate
 ```go
 import "github.com/mattes/migrate/migrate"
 
+// Import any required drivers so that they are registered and available
+import _ "github.com/mattes/migrate/drivers/mysql"
+
 // use synchronous versions of migration functions ...
 allErrors, ok := migrate.UpSync("driver://url", "./path")
 if !ok {

driver/bash/bash.go

@@ -2,6 +2,7 @@
 package bash
 
 import (
+	"github.com/mattes/migrate/driver/registry"
 	"github.com/mattes/migrate/file"
 	_ "github.com/mattes/migrate/migrate/direction"
 )
@@ -30,3 +31,7 @@ func (driver *Driver) Migrate(f file.File, pipe chan interface{}) {
 func (driver *Driver) Version() (uint64, error) {
 	return uint64(0), nil
 }
+
+func init() {
+	registry.RegisterDriver("bash", Driver{})
+}

driver/cassandra/cassandra.go

@@ -4,6 +4,7 @@ package cassandra
 import (
 	"fmt"
 	"github.com/gocql/gocql"
+	"github.com/mattes/migrate/driver/registry"
 	"github.com/mattes/migrate/file"
 	"github.com/mattes/migrate/migrate/direction"
 	"net/url"
@@ -153,3 +154,7 @@ func (driver *Driver) Version() (uint64, error) {
 	err := driver.session.Query("SELECT version FROM "+tableName+" WHERE versionRow = ?", versionRow).Scan(&version)
 	return uint64(version) - 1, err
 }
+
+func init() {
+	registry.RegisterDriver("cassandra", Driver{})
+}

driver/driver.go

@@ -5,12 +5,9 @@ import (
 	"errors"
 	"fmt"
 	neturl "net/url" // alias to allow `url string` func signature in New
+	"reflect"
 
-	"github.com/mattes/migrate/driver/bash"
-	"github.com/mattes/migrate/driver/cassandra"
-	"github.com/mattes/migrate/driver/mysql"
-	"github.com/mattes/migrate/driver/postgres"
-	"github.com/mattes/migrate/driver/sqlite3"
+	"github.com/mattes/migrate/driver/registry"
 	"github.com/mattes/migrate/file"
 )
 
@@ -47,51 +44,26 @@ func New(url string) (Driver, error) {
 		return nil, err
 	}
 
-	switch u.Scheme {
-	case "postgres":
-		d := &postgres.Driver{}
-		verifyFilenameExtension("postgres", d)
-		if err := d.Initialize(url); err != nil {
-			return nil, err
-		}
-		return d, nil
-
-	case "mysql":
-		d := &mysql.Driver{}
-		verifyFilenameExtension("mysql", d)
-		if err := d.Initialize(url); err != nil {
+	driver := registry.GetDriver(u.Scheme)
+	if driver != nil {
+		blankDriver := reflect.New(reflect.TypeOf(driver)).Interface()
+		d, ok := blankDriver.(Driver)
+		if !ok {
+			err := errors.New(fmt.Sprintf("Driver '%s' does not implement the Driver interface"))
 			return nil, err
 		}
-		return d, nil
-
-	case "bash":
-		d := &bash.Driver{}
-		verifyFilenameExtension("bash", d)
+		verifyFilenameExtension(u.Scheme, d)
 		if err := d.Initialize(url); err != nil {
 			return nil, err
 		}
-		return d, nil
 
-	case "cassandra":
-		d := &cassandra.Driver{}
-		verifyFilenameExtension("cassanda", d)
-		if err := d.Initialize(url); err != nil {
-			return nil, err
-		}
-		return d, nil
-	case "sqlite3":
-		d := &sqlite3.Driver{}
-		verifyFilenameExtension("sqlite3", d)
-		if err := d.Initialize(url); err != nil {
-			return nil, err
-		}
 		return d, nil
-	default:
+	} else {
 		return nil, errors.New(fmt.Sprintf("Driver '%s' not found.", u.Scheme))
 	}
 }
 
-// verifyFilenameExtension panics if the drivers filename extension
+// verifyFilenameExtension panics if the driver's filename extension
 // is not correct or empty.
 func verifyFilenameExtension(driverName string, d Driver) {
 	f := d.FilenameExtension()

driver/mysql/mysql.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"fmt"
 	"github.com/go-sql-driver/mysql"
+	"github.com/mattes/migrate/driver/registry"
 	"github.com/mattes/migrate/file"
 	"github.com/mattes/migrate/migrate/direction"
 	"regexp"
@@ -177,3 +178,7 @@ func (driver *Driver) Version() (uint64, error) {
 		return version, nil
 	}
 }
+
+func init() {
+	registry.RegisterDriver("mysql", Driver{})
+}

driver/postgres/postgres.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"github.com/lib/pq"
+	"github.com/mattes/migrate/driver/registry"
 	"github.com/mattes/migrate/file"
 	"github.com/mattes/migrate/migrate/direction"
 	"strconv"
@@ -119,3 +120,7 @@ func (driver *Driver) Version() (uint64, error) {
 		return version, nil
 	}
 }
+
+func init() {
+	registry.RegisterDriver("postgres", Driver{})
+}

driver/registry/registry.go

@@ -0,0 +1,20 @@
+// Package registry maintains a map of imported and available drivers
+package registry
+
+var driverRegistry map[string]interface{}
+
+// Registers a driver so it can be created from its name. Drivers should
+// call this from an init() function so that they registers themselvse on
+// import
+func RegisterDriver(name string, driver interface{}) {
+	driverRegistry[name] = driver
+}
+
+// Retrieves a registered driver by name
+func GetDriver(name string) interface{} {
+	return driverRegistry[name]
+}
+
+func init() {
+	driverRegistry = make(map[string]interface{})
+}

driver/sqlite3/sqlite3.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"github.com/mattes/migrate/driver/registry"
 	"github.com/mattes/migrate/file"
 	"github.com/mattes/migrate/migrate/direction"
 	"github.com/mattn/go-sqlite3"
@@ -123,3 +124,7 @@ func (driver *Driver) Version() (uint64, error) {
 		return version, nil
 	}
 }
+
+func init() {
+	registry.RegisterDriver("sqlite3", Driver{})
+}

migrate/migrate_test.go

@@ -3,6 +3,8 @@ package migrate
 import (
 	"io/ioutil"
 	"testing"
+	// Ensure imports for each driver we wish to test
+	_ "github.com/mattes/migrate/driver/postgres"
 )
 
 // Add Driver URLs here to test basic Up, Down, .. functions.