diff --git a/engine.go b/engine.go
index e1a9946e..146b2ee0 100644
--- a/engine.go
+++ b/engine.go
@@ -157,6 +157,20 @@ func (engine *Engine) MapOne(bean interface{}) Table {
 	return engine.MapType(t)
 }
 
+func (engine *Engine) AutoMapType(t reflect.Type) *Table {
+	table, ok := engine.Tables[t]
+	if !ok {
+		table = engine.MapType(t)
+		engine.Tables[t] = table
+	}
+	return &table
+}
+
+func (engine *Engine) AutoMap(bean interface{}) *Table {
+	t := Type(bean)
+	return engine.AutoMapType(t)
+}
+
 func (engine *Engine) MapType(t reflect.Type) Table {
 	table := Table{Name: engine.Mapper.Obj2Table(t.Name()), Type: t}
 	table.Columns = make(map[string]Column)
@@ -183,6 +197,7 @@ func (engine *Engine) MapType(t reflect.Type) Table {
 					switch {
 					case k == "pk":
 						col.IsPrimaryKey = true
+						col.Nullable = false
 						pkCol = &col
 					case k == "null":
 						col.Nullable = (tags[j-1] != "not")
diff --git a/session.go b/session.go
index 96fa79cc..70ae825d 100644
--- a/session.go
+++ b/session.go
@@ -211,7 +211,8 @@ func (session *Session) Get(bean interface{}) error {
 	statement := session.Statement
 	defer session.Statement.Init()
 	statement.Limit(1)
-	table := session.Engine.Bean2Table(bean)
+
+	table := session.Engine.AutoMap(bean)
 	statement.Table = table
 
 	colNames, args := session.BuildConditions(table, bean)
@@ -241,7 +242,7 @@ func (session *Session) Get(bean interface{}) error {
 func (session *Session) Count(bean interface{}) (int64, error) {
 	statement := session.Statement
 	defer session.Statement.Init()
-	table := session.Engine.Bean2Table(bean)
+	table := session.Engine.AutoMap(bean)
 	statement.Table = table
 
 	colNames, args := session.BuildConditions(table, bean)
@@ -271,12 +272,11 @@ func (session *Session) Find(rowsSlicePtr interface{}, condiBean ...interface{})
 	}
 
 	sliceElementType := sliceValue.Type().Elem()
-
-	table := session.Engine.Tables[sliceElementType]
-	statement.Table = &table
+	table := session.Engine.AutoMapType(sliceElementType)
+	statement.Table = table
 
 	if len(condiBean) > 0 {
-		colNames, args := session.BuildConditions(&table, condiBean[0])
+		colNames, args := session.BuildConditions(table, condiBean[0])
 		statement.ColumnStr = strings.Join(colNames, " and ")
 		statement.BeanArgs = args
 	}
@@ -428,8 +428,8 @@ func (session *Session) InsertMulti(rowsSlicePtr interface{}) (int64, error) {
 	bean := sliceValue.Index(0).Interface()
 	sliceElementType := Type(bean)
 
-	table := session.Engine.Tables[sliceElementType]
-	session.Statement.Table = &table
+	table := session.Engine.AutoMapType(sliceElementType)
+	session.Statement.Table = table
 
 	size := sliceValue.Len()
 
@@ -490,7 +490,7 @@ func (session *Session) InsertMulti(rowsSlicePtr interface{}) (int64, error) {
 }
 
 func (session *Session) InsertOne(bean interface{}) (int64, error) {
-	table := session.Engine.Bean2Table(bean)
+	table := session.Engine.AutoMap(bean)
 	session.Statement.Table = table
 	colNames := make([]string, 0)
 	colPlaces := make([]string, 0)
@@ -561,7 +561,7 @@ func (session *Session) BuildConditions(table *Table, bean interface{}) ([]strin
 }
 
 func (session *Session) Update(bean interface{}, condiBean ...interface{}) (int64, error) {
-	table := session.Engine.Bean2Table(bean)
+	table := session.Engine.AutoMap(bean)
 	session.Statement.Table = table
 	colNames, args := session.BuildConditions(table, bean)
 	var condiColNames []string
@@ -610,7 +610,7 @@ func (session *Session) Update(bean interface{}, condiBean ...interface{}) (int6
 }
 
 func (session *Session) Delete(bean interface{}) (int64, error) {
-	table := session.Engine.Bean2Table(bean)
+	table := session.Engine.AutoMap(bean)
 	session.Statement.Table = table
 	colNames, args := session.BuildConditions(table, bean)