feat: specify dbname in NewAdapter() (#41)

* feat: specify dbname in NewAdapter()

* Update adapter.go

Co-authored-by: Yang Luo <hsluoyz@qq.com>

adapter.go

@@ -13,6 +13,7 @@ import (
 )
 
 const DefaultTableName = "casbin_rule"
+const DefaultDatabaseName = "casbin"
 
 // CasbinRule represents a rule in Casbin.
 type CasbinRule struct {
@@ -43,10 +44,20 @@ type Adapter struct {
 type Option func(a *Adapter)
 
 // NewAdapter is the constructor for Adapter.
-// arg should be a PostgreS URL string or of type *pg.Options
-// The adapter will create a DB named "casbin" if it doesn't exist
-func NewAdapter(arg interface{}) (*Adapter, error) {
-	db, err := createCasbinDatabase(arg)
+// param:arg should be a PostgreS URL string or of type *pg.Options
+// param:dbname is the name of the database to use and can is optional.
+// If no dbname is provided, the default database name is "casbin" which will be created automatically.
+// If arg is *pg.Options, the arg.Database field is omitted and will be modified according to dbname
+func NewAdapter(arg interface{}, dbname ...string) (*Adapter, error) {
+	var db *pg.DB
+	var err error
+
+	if len(dbname) > 0 {
+		db, err = createCasbinDatabase(arg, dbname[0])
+	} else {
+		db, err = createCasbinDatabase(arg, DefaultDatabaseName)
+	}
+
 	if err != nil {
 		return nil, fmt.Errorf("pgadapter.NewAdapter: %v", err)
 	}
@@ -91,7 +102,7 @@ func SkipTableCreate() Option {
 	}
 }
 
-func createCasbinDatabase(arg interface{}) (*pg.DB, error) {
+func createCasbinDatabase(arg interface{}, dbname string) (*pg.DB, error) {
 	var opts *pg.Options
 	var err error
 	if connURL, ok := arg.(string); ok {
@@ -109,10 +120,13 @@ func createCasbinDatabase(arg interface{}) (*pg.DB, error) {
 	db := pg.Connect(opts)
 	defer db.Close()
 
-	_, err = db.Exec("CREATE DATABASE casbin")
+	_, err = db.Exec(fmt.Sprintf("CREATE DATABASE %s", dbname))
+	if err != nil && !strings.Contains(err.Error(), "42P04") {
+		return nil, err
+	}
 	db.Close()
 
-	opts.Database = "casbin"
+	opts.Database = dbname
 	db = pg.Connect(opts)
 
 	return db, nil