Replace all use of *sql.DB with sqlCommon

Exporting sqlCommon as SQLCommon.

This allows passing alternate implementations of the database connection, or wrapping the connection with middleware.  This change didn't change any usages of the database variables.  All usages were already only using the functions defined in SQLCommon.

This does cause a breaking change in Dialect, since *sql.DB was referenced in the interface.

dialect.go

@@ -14,7 +14,7 @@ type Dialect interface {
 	GetName() string
 
 	// SetDB set db for dialect
-	SetDB(db *sql.DB)
+	SetDB(db SQLCommon)
 
 	// BindVar return the placeholder for actual values in SQL statements, in many dbs it is "?", Postgres using $1
 	BindVar(i int) string
@@ -50,7 +50,7 @@ type Dialect interface {
 
 var dialectsMap = map[string]Dialect{}
 
-func newDialect(name string, db *sql.DB) Dialect {
+func newDialect(name string, db SQLCommon) Dialect {
 	if value, ok := dialectsMap[name]; ok {
 		dialect := reflect.New(reflect.TypeOf(value).Elem()).Interface().(Dialect)
 		dialect.SetDB(db)

dialect_common.go

@@ -1,7 +1,6 @@
 package gorm
 
 import (
-	"database/sql"
 	"fmt"
 	"reflect"
 	"regexp"
@@ -15,7 +14,7 @@ type DefaultForeignKeyNamer struct {
 }
 
 type commonDialect struct {
-	db *sql.DB
+	db SQLCommon
 	DefaultForeignKeyNamer
 }
 
@@ -27,7 +26,7 @@ func (commonDialect) GetName() string {
 	return "common"
 }
 
-func (s *commonDialect) SetDB(db *sql.DB) {
+func (s *commonDialect) SetDB(db SQLCommon) {
 	s.db = db
 }
 

dialects/mssql/mssql.go

@@ -1,7 +1,6 @@
 package mssql
 
 import (
-	"database/sql"
 	"fmt"
 	"reflect"
 	"strconv"
@@ -24,15 +23,15 @@ func init() {
 }
 
 type mssql struct {
-	db *sql.DB
+	db gorm.SQLCommon
 	gorm.DefaultForeignKeyNamer
 }
 
 func (mssql) GetName() string {
 	return "mssql"
 }
 
-func (s *mssql) SetDB(db *sql.DB) {
+func (s *mssql) SetDB(db gorm.SQLCommon) {
 	s.db = db
 }
 

interface.go

@@ -2,7 +2,8 @@ package gorm
 
 import "database/sql"
 
-type sqlCommon interface {
+// SQLCommon is the minimal database connection functionality gorm requires.  Implemented by *sql.DB.
+type SQLCommon interface {
 	Exec(query string, args ...interface{}) (sql.Result, error)
 	Prepare(query string) (*sql.Stmt, error)
 	Query(query string, args ...interface{}) (*sql.Rows, error)

main.go

@@ -16,7 +16,7 @@ type DB struct {
 	RowsAffected int64
 
 	// single db
-	db                sqlCommon
+	db                SQLCommon
 	blockGlobalUpdate bool
 	logMode           int
 	logger            logger
@@ -47,7 +47,7 @@ func Open(dialect string, args ...interface{}) (db *DB, err error) {
 		return nil, err
 	}
 	var source string
-	var dbSQL *sql.DB
+	var dbSQL SQLCommon
 
 	switch value := args[0].(type) {
 	case string:
@@ -59,8 +59,7 @@ func Open(dialect string, args ...interface{}) (db *DB, err error) {
 			source = args[1].(string)
 		}
 		dbSQL, err = sql.Open(driver, source)
-	case *sql.DB:
-		source = reflect.Indirect(reflect.ValueOf(value)).FieldByName("dsn").String()
+	case SQLCommon:
 		dbSQL = value
 	}
 
@@ -90,21 +89,27 @@ func (s *DB) New() *DB {
 	return clone
 }
 
-// Close close current db connection
+type closer interface {
+	Close() error
+}
+
+// Close close current db connection.  If database connection is not an io.Closer, returns an error.
 func (s *DB) Close() error {
-	if db, ok := s.parent.db.(*sql.DB); ok {
+	if db, ok := s.parent.db.(closer); ok {
 		return db.Close()
 	}
 	return errors.New("can't close current db")
 }
 
 // DB get `*sql.DB` from current connection
+// If the underlying database connection is not a *sql.DB, returns nil
 func (s *DB) DB() *sql.DB {
-	return s.db.(*sql.DB)
+	db, _ := s.db.(*sql.DB)
+	return db
 }
 
 // CommonDB return the underlying `*sql.DB` or `*sql.Tx` instance, mainly intended to allow coexistence with legacy non-GORM code.
-func (s *DB) CommonDB() sqlCommon {
+func (s *DB) CommonDB() SQLCommon {
 	return s.db
 }
 
@@ -449,7 +454,7 @@ func (s *DB) Begin() *DB {
 	c := s.clone()
 	if db, ok := c.db.(sqlDb); ok {
 		tx, err := db.Begin()
-		c.db = interface{}(tx).(sqlCommon)
+		c.db = interface{}(tx).(SQLCommon)
 		c.AddError(err)
 	} else {
 		c.AddError(ErrCantStartTransaction)

scope.go

@@ -58,7 +58,7 @@ func (scope *Scope) NewDB() *DB {
 }
 
 // SQLDB return *sql.DB
-func (scope *Scope) SQLDB() sqlCommon {
+func (scope *Scope) SQLDB() SQLCommon {
 	return scope.db.db
 }
 
@@ -391,7 +391,7 @@ func (scope *Scope) InstanceGet(name string) (interface{}, bool) {
 func (scope *Scope) Begin() *Scope {
 	if db, ok := scope.SQLDB().(sqlDb); ok {
 		if tx, err := db.Begin(); err == nil {
-			scope.db.db = interface{}(tx).(sqlCommon)
+			scope.db.db = interface{}(tx).(SQLCommon)
 			scope.InstanceSet("gorm:started_transaction", true)
 		}
 	}