New construct method for creating adapter from existing DB connection

adapter.go

@@ -56,6 +56,16 @@ func NewAdapter(arg interface{}) (*Adapter, error) {
 	return a, nil
 }
 
+// NewAdapterByDB creates new Adapter by using existing DB connection
+// creates table from CasbinRule struct if it doesn't exist
+func NewAdapterByDB(db *pg.DB) (*Adapter, error) {
+	a := &Adapter{db: db}
+	if err := a.createTable(); err != nil {
+		return nil, fmt.Errorf("pgadapter.NewAdapter: %v", err)
+	}
+	return a, nil
+}
+
 func createCasbinDatabase(arg interface{}) (*pg.DB, error) {
 	var opts *pg.Options
 	var err error

go.mod

@@ -3,7 +3,6 @@ module github.com/casbin/casbin-pg-adapter
 go 1.12
 
 require (
-	github.com/casbin/casbin v1.9.1
 	github.com/casbin/casbin/v2 v2.1.2
 	github.com/go-pg/pg/v9 v9.1.0
 	github.com/mmcloughlin/meow v0.0.0-20181112033425-871e50784daf

go.sum

 github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible h1:1G1pk05UrOh0NlF1oeaaix1x8XzrfjIDK47TY0Zehcw=
 github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible/go.mod h1:r7JcOSlj0wfOMncg0iLm8Leh48TZaKVeNIfJntJ2wa0=
-github.com/casbin/casbin v1.9.1 h1:ucjbS5zTrmSLtH4XogqOG920Poe6QatdXtz1FEbApeM=
-github.com/casbin/casbin v1.9.1/go.mod h1:z8uPsfBJGUsnkagrt3G8QvjgTKFMBJ32UP8HpZllfog=
 github.com/casbin/casbin/v2 v2.1.2 h1:bTwon/ECRx9dwBy2ewRVr5OiqjeXSGiTUY74sDPQi/g=
 github.com/casbin/casbin/v2 v2.1.2/go.mod h1:YcPU1XXisHhLzuxH9coDNf2FbKpjGlbCg3n9yuLkIJQ=
 github.com/codemodus/kace v0.5.1 h1:4OCsBlE2c/rSJo375ggfnucv9eRzge/U5LrrOZd47HA=