diff --git a/schema/relationship.go b/schema/relationship.go
index 95f56f6d..5081d540 100644
--- a/schema/relationship.go
+++ b/schema/relationship.go
@@ -25,15 +25,15 @@ type Relationships struct {
 }
 
 type Relationship struct {
-	Name                                string
-	Type                                RelationshipType
-	Field                               *Field
-	Polymorphic                         *Polymorphic
-	References                          []Reference
-	Schema                              *Schema
-	FieldSchema                         *Schema
-	JoinTable                           *Schema
-	ForeignKeys, AssociationForeignKeys []string
+	Name                     string
+	Type                     RelationshipType
+	Field                    *Field
+	Polymorphic              *Polymorphic
+	References               []Reference
+	Schema                   *Schema
+	FieldSchema              *Schema
+	JoinTable                *Schema
+	ForeignKeys, PrimaryKeys []string
 }
 
 type Polymorphic struct {
@@ -53,12 +53,11 @@ func (schema *Schema) parseRelation(field *Field) {
 	var (
 		fieldValue = reflect.New(field.FieldType).Interface()
 		relation   = &Relationship{
-			Name:                   field.Name,
-			Field:                  field,
-			Schema:                 schema,
-			Type:                   RelationshipType(strings.ToLower(strings.TrimSpace(field.TagSettings["REL"]))),
-			ForeignKeys:            toColumns(field.TagSettings["FOREIGNKEY"]),
-			AssociationForeignKeys: toColumns(field.TagSettings["ASSOCIATION_FOREIGNKEY"]),
+			Name:        field.Name,
+			Field:       field,
+			Schema:      schema,
+			ForeignKeys: toColumns(field.TagSettings["FOREIGNKEY"]),
+			PrimaryKeys: toColumns(field.TagSettings["PRIMARYKEY"]),
 		}
 	)
 
@@ -66,6 +65,8 @@ func (schema *Schema) parseRelation(field *Field) {
 		return
 	}
 
+	// Parse Polymorphic relations
+	//
 	// User has many Toys, its `Polymorphic` is `Owner`, Pet has one Toy, its `Polymorphic` is `Owner`
 	//     type User struct {
 	//       Toys []Toy `gorm:"polymorphic:Owner;"`
@@ -89,11 +90,11 @@ func (schema *Schema) parseRelation(field *Field) {
 		}
 
 		if relation.Polymorphic.PolymorphicType == nil {
-			schema.err = fmt.Errorf("invalid polymorphic type: %v for %v on field %v, missing field %v", relation.FieldSchema, schema, field.Name, polymorphic+"Type")
+			schema.err = fmt.Errorf("invalid polymorphic type %v for %v on field %v, missing field %v", relation.FieldSchema, schema, field.Name, polymorphic+"Type")
 		}
 
 		if relation.Polymorphic.PolymorphicID == nil {
-			schema.err = fmt.Errorf("invalid polymorphic type: %v for %v on field %v, missing field %v", relation.FieldSchema, schema, field.Name, polymorphic+"ID")
+			schema.err = fmt.Errorf("invalid polymorphic type %v for %v on field %v, missing field %v", relation.FieldSchema, schema, field.Name, polymorphic+"ID")
 		}
 
 		if schema.err == nil {
@@ -105,7 +106,7 @@ func (schema *Schema) parseRelation(field *Field) {
 			primaryKeyField := schema.PrioritizedPrimaryField
 			if len(relation.ForeignKeys) > 0 {
 				if primaryKeyField = schema.LookUpField(relation.ForeignKeys[0]); primaryKeyField == nil || len(relation.ForeignKeys) > 1 {
-					schema.err = fmt.Errorf("invalid polymorphic foreign key: %+v for %v on field %v", relation.ForeignKeys, schema, field.Name)
+					schema.err = fmt.Errorf("invalid polymorphic foreign keys %+v for %v on field %v", relation.ForeignKeys, schema, field.Name)
 				}
 			}
 			relation.References = append(relation.References, Reference{
@@ -115,29 +116,108 @@ func (schema *Schema) parseRelation(field *Field) {
 			})
 		}
 
+		relation.Type = "has"
+	} else {
+		switch field.FieldType.Kind() {
+		case reflect.Struct:
+			schema.guessRelation(relation, field, true)
+		case reflect.Slice:
+			schema.guessRelation(relation, field, true)
+		default:
+			schema.err = fmt.Errorf("unsupported data type %v for %v on field %v", relation.FieldSchema, schema, field.Name)
+		}
+	}
+
+	if relation.Type == "has" {
 		switch field.FieldType.Kind() {
 		case reflect.Struct:
 			relation.Type = HasOne
 		case reflect.Slice:
 			relation.Type = HasMany
 		}
+	}
+}
+
+func (schema *Schema) guessRelation(relation *Relationship, field *Field, guessHas bool) {
+	var (
+		primaryFields, foreignFields []*Field
+		primarySchema, foreignSchema = schema, relation.FieldSchema
+	)
+
+	if !guessHas {
+		primarySchema, foreignSchema = relation.FieldSchema, schema
+	}
+
+	reguessOrErr := func(err string, args ...interface{}) {
+		if guessHas {
+			schema.guessRelation(relation, field, false)
+		} else {
+			schema.err = fmt.Errorf(err, args...)
+		}
+	}
+
+	if len(relation.ForeignKeys) > 0 {
+		for _, foreignKey := range relation.ForeignKeys {
+			if f := foreignSchema.LookUpField(foreignKey); f != nil {
+				foreignFields = append(foreignFields, f)
+			} else {
+				reguessOrErr("unsupported relations %v for %v on field %v with foreign keys %v", relation.FieldSchema, schema, field.Name, relation.ForeignKeys)
+				return
+			}
+		}
+	} else {
+		for _, primaryField := range primarySchema.PrimaryFields {
+			if f := foreignSchema.LookUpField(field.Name + primaryField.Name); f != nil {
+				foreignFields = append(foreignFields, f)
+				primaryFields = append(primaryFields, primaryField)
+			}
+		}
+	}
+
+	if len(foreignFields) == 0 {
+		reguessOrErr("failed to guess %v's relations with %v's field %v", relation.FieldSchema, schema, field.Name)
 		return
+	} else if len(relation.PrimaryKeys) > 0 {
+		for idx, primaryKey := range relation.PrimaryKeys {
+			if f := primarySchema.LookUpField(primaryKey); f != nil {
+				if len(primaryFields) < idx+1 {
+					primaryFields = append(primaryFields, f)
+				} else if f != primaryFields[idx] {
+					reguessOrErr("unsupported relations %v for %v on field %v with primary keys %v", relation.FieldSchema, schema, field.Name, relation.PrimaryKeys)
+					return
+				}
+			} else {
+				reguessOrErr("unsupported relations %v for %v on field %v with primary keys %v", relation.FieldSchema, schema, field.Name, relation.PrimaryKeys)
+				return
+			}
+		}
+	} else if len(primaryFields) == 0 {
+		if len(foreignFields) == 1 {
+			primaryFields = append(primaryFields, primarySchema.PrioritizedPrimaryField)
+		} else if len(primarySchema.PrimaryFields) == len(foreignFields) {
+			primaryFields = append(primaryFields, primarySchema.PrimaryFields...)
+		} else {
+			reguessOrErr("unsupported relations %v for %v on field %v", relation.FieldSchema, schema, field.Name)
+			return
+		}
 	}
 
-	switch field.FieldType.Kind() {
-	case reflect.Struct:
-		schema.parseStructRelation(relation, field)
-	case reflect.Slice:
-		schema.parseSliceRelation(relation, field)
-	default:
-		schema.err = fmt.Errorf("unsupported data type: %v (in %v#%v ", field.FieldType.PkgPath(), schema, field.Name)
+	// build references
+	for idx, foreignField := range foreignFields {
+		relation.References = append(relation.References, Reference{
+			PriamryKey:    primaryFields[idx],
+			ForeignKey:    foreignField,
+			OwnPriamryKey: schema == primarySchema,
+		})
+	}
+
+	if guessHas {
+		relation.Type = "has"
+	} else {
+		relation.Type = "belongs_to"
 	}
 }
 
-func (schema *Schema) parseStructRelation(relation *Relationship, field *Field) error {
-	return nil
-}
-
-func (schema *Schema) parseSliceRelation(relation *Relationship, field *Field) error {
+func (schema *Schema) parseMany2ManyRelation(relation *Relationship, field *Field) error {
 	return nil
 }