feat: support inner join (#5583)

* feat: support inner join

* test: mixed inner join and left join

* chore: code comment

* Update statement.go

Co-authored-by: Jinzhu <wosmvp@gmail.com>

callbacks/query.go

@@ -185,7 +185,7 @@ func BuildQuerySQL(db *gorm.DB) {
 					}
 
 					fromClause.Joins = append(fromClause.Joins, clause.Join{
-						Type:  clause.LeftJoin,
+						Type:  join.JoinType,
 						Table: clause.Table{Name: relation.FieldSchema.Table, Alias: tableAliasName},
 						ON:    clause.Where{Exprs: exprs},
 					})

chainable_api.go

@@ -235,6 +235,16 @@ func (db *DB) Or(query interface{}, args ...interface{}) (tx *DB) {
 //	db.Joins("JOIN emails ON emails.user_id = users.id AND emails.email = ?", "jinzhu@example.org").Find(&user)
 //	db.Joins("Account", DB.Select("id").Where("user_id = users.id AND name = ?", "someName").Model(&Account{}))
 func (db *DB) Joins(query string, args ...interface{}) (tx *DB) {
+	return joins(db, clause.LeftJoin, query, args...)
+}
+
+// InnerJoins specify inner joins conditions
+// db.InnerJoins("Account").Find(&user)
+func (db *DB) InnerJoins(query string, args ...interface{}) (tx *DB) {
+	return joins(db, clause.InnerJoin, query, args...)
+}
+
+func joins(db *DB, joinType clause.JoinType, query string, args ...interface{}) (tx *DB) {
 	tx = db.getInstance()
 
 	if len(args) == 1 {
@@ -248,7 +258,7 @@ func (db *DB) Joins(query string, args ...interface{}) (tx *DB) {
 		}
 	}
 
-	tx.Statement.Joins = append(tx.Statement.Joins, join{Name: query, Conds: args})
+	tx.Statement.Joins = append(tx.Statement.Joins, join{Name: query, Conds: args, JoinType: joinType})
 	return
 }
 

statement.go

@@ -54,6 +54,7 @@ type join struct {
 	On       *clause.Where
 	Selects  []string
 	Omits    []string
+	JoinType clause.JoinType
 }
 
 // StatementModifier statement modifier interface

tests/joins_test.go

@@ -230,6 +230,28 @@ func TestJoinWithSoftDeleted(t *testing.T) {
 	}
 }
 
+func TestInnerJoins(t *testing.T) {
+	user := *GetUser("inner-joins-1", Config{Company: true, Manager: true, Account: true, NamedPet: false})
+
+	DB.Create(&user)
+
+	var user2 User
+	var err error
+	err = DB.InnerJoins("Company").InnerJoins("Manager").InnerJoins("Account").First(&user2, "users.name = ?", user.Name).Error
+	AssertEqual(t, err, nil)
+	CheckUser(t, user2, user)
+
+	// inner join and NamedPet is nil
+	err = DB.InnerJoins("NamedPet").InnerJoins("Company").InnerJoins("Manager").InnerJoins("Account").First(&user2, "users.name = ?", user.Name).Error
+	AssertEqual(t, err, gorm.ErrRecordNotFound)
+
+	// mixed inner join and left join
+	var user3 User
+	err = DB.Joins("NamedPet").InnerJoins("Company").InnerJoins("Manager").InnerJoins("Account").First(&user3, "users.name = ?", user.Name).Error
+	AssertEqual(t, err, nil)
+	CheckUser(t, user3, user)
+}
+
 func TestJoinWithSameColumnName(t *testing.T) {
 	user := GetUser("TestJoinWithSameColumnName", Config{
 		Languages: 1,