Add db.ToSQL method for generate SQL string.

gorm.go

@@ -439,3 +439,18 @@ func (db *DB) Use(plugin Plugin) error {
 	db.Plugins[name] = plugin
 	return nil
 }
+
+// ToSQL for generate SQL string.
+//
+// db.ToSQL(func(tx *gorm.DB) *gorm.DB {
+// 		return tx.Model(&User{}).Where(&User{Name: "foo", Age: 20})
+// 			.Limit(10).Offset(5)
+//			.Order("name ASC")
+//			.First(&User{})
+// })
+func (db *DB) ToSQL(queryFn func(tx *DB) *DB) string {
+	tx := queryFn(db.Session(&Session{DryRun: true}))
+	stmt := tx.Statement
+
+	return db.Dialector.Explain(stmt.SQL.String(), stmt.Vars...)
+}

tests/sql_builder_test.go

@@ -8,6 +8,8 @@ import (
 	"gorm.io/gorm"
 	"gorm.io/gorm/clause"
 	. "gorm.io/gorm/utils/tests"
+	"os"
+	"time"
 )
 
 func TestRow(t *testing.T) {
@@ -287,3 +289,109 @@ func TestFromWithJoins(t *testing.T) {
 		t.Errorf("The first join condition is over written instead of combining")
 	}
 }
+
+func TestToSQL(t *testing.T) {
+	// only test in PostgreSQL
+	var dialect = os.Getenv("GORM_DIALECT")
+	if dialect != "postgres" {
+		t.Skipf("Skipping test for %s database", dialect)
+		return
+	}
+
+	// By default DB.DryRun should false
+	if DB.DryRun {
+		t.Fatal("Failed expect DB.DryRun to be false")
+	}
+
+	date, _ := time.Parse("2006-01-02", "2021-10-18")
+
+	// find
+	sql := DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Where("id = ?", 100).Limit(10).Order("age desc").Find(&[]User{})
+	})
+	assertEqualSQL(t, `SELECT * FROM "users" WHERE id = 100 AND "users"."deleted_at" IS NULL ORDER BY age desc LIMIT 10`, sql)
+
+	// after model chagned
+	if DB.Statement.DryRun || DB.DryRun {
+		t.Fatal("Failed expect DB.DryRun and DB.Statement.ToSQL to be false")
+	}
+
+	if DB.Statement.SQL.String() != "" {
+		t.Fatal("Failed expect DB.Statement.SQL to be empty")
+	}
+
+	// first
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Where(&User{Name: "foo", Age: 20}).Limit(10).Offset(5).Order("name ASC").First(&User{})
+	})
+	assertEqualSQL(t, `SELECT * FROM "users" WHERE "users"."name" = 'foo' AND "users"."age" = 20 AND "users"."deleted_at" IS NULL ORDER BY name ASC,"users"."id" LIMIT 1 OFFSET 5`, sql)
+
+	// last and unscoped
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Unscoped().Where(&User{Name: "bar", Age: 12}).Limit(10).Offset(5).Order("name ASC").Last(&User{})
+	})
+	assertEqualSQL(t, `SELECT * FROM "users" WHERE "users"."name" = 'bar' AND "users"."age" = 12 ORDER BY name ASC,"users"."id" DESC LIMIT 1 OFFSET 5`, sql)
+
+	// create
+	user := &User{Name: "foo", Age: 20}
+	user.CreatedAt = date
+	user.UpdatedAt = date
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Create(user)
+	})
+	assertEqualSQL(t, `INSERT INTO "users" ("created_at","updated_at","deleted_at","name","age","birthday","company_id","manager_id","active") VALUES ('2021-10-18 00:00:00','2021-10-18 00:00:00',NULL,'foo',20,NULL,NULL,NULL,false) RETURNING "id"`, sql)
+
+	// save
+	user = &User{Name: "foo", Age: 20}
+	user.CreatedAt = date
+	user.UpdatedAt = date
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Save(user)
+	})
+	assertEqualSQL(t, `INSERT INTO "users" ("created_at","updated_at","deleted_at","name","age","birthday","company_id","manager_id","active") VALUES ('2021-10-18 00:00:00','2021-10-18 00:00:00',NULL,'foo',20,NULL,NULL,NULL,false) RETURNING "id"`, sql)
+
+	// updates
+	user = &User{Name: "bar", Age: 22}
+	user.CreatedAt = date
+	user.UpdatedAt = date
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Where("id = ?", 100).Updates(user)
+	})
+	assertEqualSQL(t, `UPDATE "users" SET "created_at"='2021-10-18 00:00:00',"updated_at"='2021-10-18 19:50:09.438',"name"='bar',"age"=22 WHERE id = 100 AND "users"."deleted_at" IS NULL`, sql)
+
+	// update
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Where("id = ?", 100).Update("name", "Foo bar")
+	})
+	assertEqualSQL(t, `UPDATE "users" SET "name"='Foo bar',"updated_at"='2021-10-18 19:50:09.438' WHERE id = 100 AND "users"."deleted_at" IS NULL`, sql)
+
+	// UpdateColumn
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Where("id = ?", 100).UpdateColumn("name", "Foo bar")
+	})
+	assertEqualSQL(t, `UPDATE "users" SET "name"='Foo bar' WHERE id = 100 AND "users"."deleted_at" IS NULL`, sql)
+
+	// UpdateColumns
+	sql = DB.ToSQL(func(tx *gorm.DB) *gorm.DB {
+		return tx.Model(&User{}).Where("id = ?", 100).UpdateColumns(User{Name: "Foo", Age: 100})
+	})
+	assertEqualSQL(t, `UPDATE "users" SET "name"='Foo',"age"=100 WHERE id = 100 AND "users"."deleted_at" IS NULL`, sql)
+
+	// after model chagned
+	if DB.Statement.DryRun || DB.DryRun {
+		t.Fatal("Failed expect DB.DryRun and DB.Statement.ToSQL to be false")
+	}
+}
+
+func assertEqualSQL(t *testing.T, expected string, actually string) {
+	t.Helper()
+
+	// ignore updated_at value
+	var updatedAtRe = regexp.MustCompile(`"updated_at"='.+?'`)
+	actually = updatedAtRe.ReplaceAllString(actually, `"updated_at"='?'`)
+	expected = updatedAtRe.ReplaceAllString(expected, `"updated_at"='?'`)
+
+	if actually != expected {
+		t.Fatalf("Failed generate save SQL\nexpected: %s\nactually: %s", expected, actually)
+	}
+}