feat(generate): preload with offset and limit

README.ZH_CN.md

@@ -115,6 +115,7 @@
           - [`If` 子句](#if-clause)
           - [`Where` 子句](#where-clause)
           - [`Set` 子句](#set-clause)
+          - [`For` 子句](#for-clause)
         - [方法接口示例](#method-interface-example)
       - [单元测试](#unit-test)
       - [智能选择字段](#smart-select-fields)
@@ -1424,7 +1425,7 @@ users, err := u.WithContext(ctx).Preload(u.Orders.OrderItems.Product).Find()
 
 ###### <span id="nested-preloading">根据条件预加载</span>
 
-GORM 允许预加载与条件关联，它的工作原理类似于内联条件。
+GEN 允许预加载与条件关联，它的工作原理类似于内联条件。
 
 ```go
 q := query.Use(db)
@@ -1451,6 +1452,10 @@ users, err := u.WithContext(ctx).Preload(u.Orders.On(o.State.Eq("on")).Order(o.I
 users, err := u.WithContext(ctx).Preload(u.Orders.Clauses(hints.UseIndex("idx_order_id"))).Find()
 // SELECT * FROM users;
 // SELECT * FROM orders WHERE user_id IN (1,2) USE INDEX (`idx_order_id`);
+
+user, err := u.WithContext(ctx).Where(u.ID.Eq(1)).Preload(u.Orders.Offset(100).Limit(20)).Take()
+// SELECT * FROM users WHERE `user_id` = 1 LIMIT 20 OFFSET 100;
+// SELECT * FROM `users` WHERE `users`.`id` = 1 LIMIT 1
 ```
 
 ###### <span id="nested-preloading">嵌套预加载</span>
@@ -1762,7 +1767,7 @@ update @@table
 where id=@id
 ```
 
-###### `For` 子句
+###### <span id="for-clause">`For` 子句</span>
 
 ```
 {{for _,name:=range names}}

README.md

@@ -116,6 +116,7 @@ Gen: Friendly & Safer [GORM](https://github.com/go-gorm/gorm) powered by Code Ge
           - [`If` clause](#if-clause)
           - [`Where` clause](#where-clause)
           - [`Set` clause](#set-clause)
+          - [`For` clause](#for-clause)
         - [Method interface example](#method-interface-example)
       - [Unit Test](#unit-test)
       - [Smart select fields](#smart-select-fields)
@@ -1428,7 +1429,7 @@ users, err := u.WithContext(ctx).Preload(u.Orders.OrderItems.Product).Find()
 
 ###### Preload with conditions
 
-GORM allows Preload associations with conditions, it works similar to Inline Conditions.
+GEN allows Preload associations with conditions, it works similar to Inline Conditions.
 
 ```go
 q := query.Use(db)
@@ -1455,6 +1456,10 @@ users, err := u.WithContext(ctx).Preload(u.Orders.On(o.State.Eq("on")).Order(o.I
 users, err := u.WithContext(ctx).Preload(u.Orders.Clauses(hints.UseIndex("idx_order_id"))).Find()
 // SELECT * FROM users;
 // SELECT * FROM orders WHERE user_id IN (1,2) USE INDEX (`idx_order_id`);
+
+user, err := u.WithContext(ctx).Where(u.ID.Eq(1)).Preload(u.Orders.Offset(100).Limit(20)).Take()
+// SELECT * FROM users WHERE `user_id` = 1 LIMIT 20 OFFSET 100;
+// SELECT * FROM `users` WHERE `users`.`id` = 1 LIMIT 1
 ```
 
 ###### Nested Preloading

do.go

@@ -357,6 +357,11 @@ func (d *DO) Preload(field field.RelationField) Dao {
 			return db.Clauses(clauses...)
 		})
 	}
+	if offset, limit := field.GetPage(); offset|limit != 0 {
+		args = append(args, func(db *gorm.DB) *gorm.DB {
+			return db.Offset(offset).Limit(limit)
+		})
+	}
 	return d.getInstance(d.db.Preload(field.Path(), args...))
 }
 

field/association.go

@@ -27,10 +27,13 @@ type RelationField interface {
 	On(conds ...Expr) RelationField
 	Order(columns ...Expr) RelationField
 	Clauses(hints ...clause.Expression) RelationField
+	Offset(offset int) RelationField
+	Limit(limit int) RelationField
 
 	GetConds() []Expr
 	GetOrderCol() []Expr
 	GetClauses() []clause.Expression
+	GetPage() (offset, limit int)
 }
 
 type Relation struct {
@@ -43,9 +46,10 @@ type Relation struct {
 
 	childRelations []Relation
 
-	conds   []Expr
-	order   []Expr
-	clauses []clause.Expression
+	conds         []Expr
+	order         []Expr
+	clauses       []clause.Expression
+	limit, offset int
 }
 
 func (r Relation) Name() string { return r.fieldName }
@@ -77,22 +81,27 @@ func (r Relation) On(conds ...Expr) RelationField {
 	r.conds = append(r.conds, conds...)
 	return &r
 }
-
 func (r Relation) Order(columns ...Expr) RelationField {
 	r.order = append(r.order, columns...)
 	return &r
 }
-
 func (r Relation) Clauses(hints ...clause.Expression) RelationField {
 	r.clauses = append(r.clauses, hints...)
 	return &r
 }
+func (r Relation) Offset(offset int) RelationField {
+	r.offset = offset
+	return &r
+}
+func (r Relation) Limit(limit int) RelationField {
+	r.limit = limit
+	return &r
+}
 
-func (r *Relation) GetConds() []Expr { return r.conds }
-
-func (r *Relation) GetOrderCol() []Expr { return r.order }
-
+func (r *Relation) GetConds() []Expr                { return r.conds }
+func (r *Relation) GetOrderCol() []Expr             { return r.order }
 func (r *Relation) GetClauses() []clause.Expression { return r.clauses }
+func (r *Relation) GetPage() (offset, limit int)    { return r.offset, r.limit }
 
 func (r *Relation) StructMember() string {
 	var memberStr string