Fix: Unexpected OR Conditions force converted to AND

[Riseif]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

Fix a bug I found.

User Case Description

• When there is only one OR clause inside a where clause, we want ignore the OR condition and just make it AND.

However, current implementation didn't check when actually there are multi expressions inside OR condition, these expressions are not expected to be modified to AND.

Check the demo below.

package main

import (
	"fmt"

	"gorm.io/driver/sqlite"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

type User struct {
	ID   uint
	Name string
	Age  int
}

func main() {
	db, _ := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
	db.AutoMigrate(&User{})

	// insert data
	db.Create(&User{Name: "Alice", Age: 30})
	db.Create(&User{Name: "Bob", Age: 25})

	sub := db.Clauses(clause.Where{
		Exprs: []clause.Expression{
			clause.OrConditions{
				Exprs: []clause.Expression{
					clause.Expr{SQL: "name = ?", Vars: []interface{}{"Alice"}},
					clause.Expr{SQL: "age = ?", Vars: []interface{}{25}},
				},
			},
		},
	})

	db = db.Debug().Model(&User{})
	var users []User
	db.Where(sub).Find(&users)

	fmt.Println("result：")
	for _, u := range users {
		fmt.Printf("ID=%d Name=%s Age=%d\n", u.ID, u.Name, u.Age)
	}
}

Before

[0.012ms] [rows:0] SELECT * FROM `users` WHERE name = "Alice" AND age = 25
result：

After

[0.018ms] [rows:2] SELECT * FROM `users` WHERE (name = "Alice" OR age = 25)
result：
ID=1 Name=Alice Age=30
ID=2 Name=Bob Age=25