Support deferred constraints

schema/relationship.go

@@ -631,6 +631,7 @@ type Constraint struct {
 	References      []*Field
 	OnDelete        string
 	OnUpdate        string
+	Deferrable      string
 }
 
 func (constraint *Constraint) GetName() string { return constraint.Name }
@@ -645,6 +646,10 @@ func (constraint *Constraint) Build() (sql string, vars []interface{}) {
 		sql += " ON UPDATE " + constraint.OnUpdate
 	}
 
+	if constraint.Deferrable != "" {
+		sql += " DEFERRABLE " + constraint.Deferrable
+	}
+
 	foreignKeys := make([]interface{}, 0, len(constraint.ForeignKeys))
 	for _, field := range constraint.ForeignKeys {
 		foreignKeys = append(foreignKeys, clause.Column{Name: field.DBName})
@@ -700,10 +705,11 @@ func (rel *Relationship) ParseConstraint() *Constraint {
 	}
 
 	constraint := Constraint{
-		Name:     name,
-		Field:    rel.Field,
-		OnUpdate: settings["ONUPDATE"],
-		OnDelete: settings["ONDELETE"],
+		Name:       name,
+		Field:      rel.Field,
+		OnUpdate:   settings["ONUPDATE"],
+		OnDelete:   settings["ONDELETE"],
+		Deferrable: strings.ToUpper(settings["DEFERRABLE"]),
 	}
 
 	for _, ref := range rel.References {

schema/relationship_test.go

@@ -1,6 +1,7 @@
 package schema_test
 
 import (
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -1041,3 +1042,32 @@ func TestDataRace(t *testing.T) {
 		}()
 	}
 }
+
+func TestDeferrable(t *testing.T) {
+	type Profile struct {
+		gorm.Model
+		Name   string
+		User   User
+		UserId uint
+	}
+
+	type User struct {
+		gorm.Model
+		Profile Profile `gorm:"constraint:deferrable:initially deferred"`
+	}
+
+	s, err := schema.Parse(&User{}, &sync.Map{}, schema.NamingStrategy{})
+	if err != nil {
+		t.Fatalf("failed to parse schema")
+	}
+
+	constraint := s.Relationships.Relations["Profile"].ParseConstraint()
+	if constraint.Deferrable != "INITIALLY DEFERRED" {
+		t.Fatalf("expected deferrable INITIALLY DEFERRED, got %v", constraint.Deferrable)
+	}
+
+	sql, _ := constraint.Build()
+	if !strings.Contains(sql, "DEFERRABLE INITIALLY DEFERRED") {
+		t.Fatalf("expected deferrable in sql, got %v", sql)
+	}
+}