From a8d3a3561df98214dbf2559249eacc38335ffe6e Mon Sep 17 00:00:00 2001
From: riverchu <churiver@outlook.com>
Date: Wed, 22 Sep 2021 19:34:58 +0800
Subject: [PATCH] feat: implement relation

---
 do.go                       | 12 ++++++------
 field/export.go             |  2 ++
 field/relation.go           | 17 +++++++++++++++++
 interface.go                |  4 ++--
 internal/template/method.go | 12 ++++++------
 5 files changed, 33 insertions(+), 14 deletions(-)
 create mode 100644 field/relation.go

diff --git a/do.go b/do.go
index bc6d7741..a985ad50 100644
--- a/do.go
+++ b/do.go
@@ -282,10 +282,6 @@ func (d *DO) Unscoped() Dao {
 	return d.getInstance(d.db.Unscoped())
 }
 
-func (d *DO) Joins(table schema.Tabler, on ...field.Expr) Dao {
-	return d.getInstance(d.db.Joins(table.TableName(), toExpressionInterface(on...)...))
-}
-
 func (d *DO) Join(table schema.Tabler, conds ...field.Expr) Dao {
 	return d.join(table, clause.InnerJoin, conds)
 }
@@ -320,8 +316,12 @@ func (d *DO) Assign(attrs ...field.Expr) Dao {
 	return d.getInstance(d.db.Assign(toExpressionInterface(attrs...)...))
 }
 
-func (d *DO) Preload(column field.Expr, on ...field.Expr) Dao {
-	return d.getInstance(d.db.Preload(column.ColumnName().String(), toExpressionInterface(on...)...))
+func (d *DO) Joins(column field.RelationPath, on ...field.Expr) Dao {
+	return d.getInstance(d.db.Joins(string(column.Path()), toExpressionInterface(on...)...))
+}
+
+func (d *DO) Preload(column field.RelationPath, on ...field.Expr) Dao {
+	return d.getInstance(d.db.Preload(string(column.Path()), toExpressionInterface(on...)...))
 }
 
 func getFromClause(db *gorm.DB) *clause.From {
diff --git a/field/export.go b/field/export.go
index 952c82a7..739c6d39 100644
--- a/field/export.go
+++ b/field/export.go
@@ -214,3 +214,5 @@ func ContainsValue(columns []Expr, value Value) Expr {
 }
 
 func EmptyExpr() Expr { return expr{e: clause.Expr{}} }
+
+func NewRelation(varName string) Relation { return Relation{varName: varName} }
diff --git a/field/relation.go b/field/relation.go
new file mode 100644
index 00000000..6930ea74
--- /dev/null
+++ b/field/relation.go
@@ -0,0 +1,17 @@
+package field
+
+type RelationPath interface {
+	Path() relationPath
+}
+
+type relationPath string
+
+func (p relationPath) Path() relationPath { return p }
+
+type Relation struct {
+	varName string
+}
+
+func (r Relation) Path() relationPath {
+	return relationPath(r.varName)
+}
diff --git a/interface.go b/interface.go
index 094f4630..c5bab4bb 100644
--- a/interface.go
+++ b/interface.go
@@ -48,7 +48,6 @@ type Dao interface {
 	Order(columns ...field.Expr) Dao
 	Distinct(columns ...field.Expr) Dao
 	Omit(columns ...field.Expr) Dao
-	Joins(table schema.Tabler, on ...field.Expr) Dao
 	Join(table schema.Tabler, conds ...field.Expr) Dao
 	LeftJoin(table schema.Tabler, conds ...field.Expr) Dao
 	RightJoin(table schema.Tabler, conds ...field.Expr) Dao
@@ -60,7 +59,8 @@ type Dao interface {
 	Unscoped() Dao
 	Attrs(attrs ...field.Expr) Dao
 	Assign(attrs ...field.Expr) Dao
-	Preload(column field.Expr, on ...field.Expr) Dao
+	Joins(column field.RelationPath, on ...field.Expr) Dao
+	Preload(column field.RelationPath, on ...field.Expr) Dao
 
 	Create(value interface{}) error
 	CreateInBatches(value interface{}, batchSize int) error
diff --git a/internal/template/method.go b/internal/template/method.go
index 3ae6c164..bf6d8ba0 100644
--- a/internal/template/method.go
+++ b/internal/template/method.go
@@ -60,11 +60,6 @@ func ({{.S}} {{.NewStructName}}Do) Omit(cols ...field.Expr) *{{.NewStructName}}D
 	return {{.S}}.withDO({{.S}}.DO.Omit(cols...))
 }
 
-// Joins eager preloading
-func ({{.S}} {{.NewStructName}}Do) Joins(table schema.Tabler, on ...field.Expr) *{{.NewStructName}}Do {
-	return {{.S}}.withDO({{.S}}.DO.Joins(table, on...))
-}
-
 func ({{.S}} {{.NewStructName}}Do) Join(table schema.Tabler, on ...field.Expr) *{{.NewStructName}}Do {
 	return {{.S}}.withDO({{.S}}.DO.Join(table, on...))
 }
@@ -165,7 +160,12 @@ func ({{.S}} {{.NewStructName}}Do) Assign(attrs ...field.Expr) *{{.NewStructName
 	return {{.S}}.withDO({{.S}}.DO.Assign(attrs...))
 }
 
-func ({{.S}} {{.NewStructName}}Do) Preload(column field.Expr, on ...field.Expr) *{{.NewStructName}}Do {
+// Joins eager preloading
+func ({{.S}} {{.NewStructName}}Do) Joins(column field.RelationPath, on ...field.Expr) *{{.NewStructName}}Do {
+	return {{.S}}.withDO({{.S}}.DO.Joins(column, on...))
+}
+
+func ({{.S}} {{.NewStructName}}Do) Preload(column field.RelationPath, on ...field.Expr) *{{.NewStructName}}Do {
 	return {{.S}}.withDO({{.S}}.DO.Preload(column, on...))
 }