我是 GOlang 和 GORM 的新手,我对如何使用 GORM 进行多表连接有些困惑。
示例:
表格:
Department - Fields (gorm.Modal, dep_name)
Employee - Fields (gorm.Modal, emp_id, emp_name, department_id) //employee is department table child
EmployeeContact - Fields (gorm.Modal, employee_id, emp_contact_no)//Employee contact table is employee table child
查询
SELECT * FROM department d, employee e, employeeContact ec WHERE d.id = e.department_id and e.id = ec.employee_id
如何使用 GORM 进行上述查询?
我一直在这里寻找解决方案,但由于我已经自己弄清楚了,所以我也想将其发布在这里。我的查询有点不同,我只加入了 2 个表,但我认为这个也应该有效。
if err := db.Table("employee").Select("department.id, employee.department_id, employeeContact.employee_id").Joins("JOIN department on department.id = employee.department_id").Joins("JOIN employeeContact on employeeContact.id = employee.id").Find(&results).Error; err != nil {
return err, ""
}
您可以使用
Preload
但请注意,预加载并未针对此查询进行优化
首先,假设已经定义了模型:
type Department struct{
gorm.Modal
DepName string
Employees *[]Employee
}
type Employee struct{
gorm.Modal
EmpId int
EmpName string
DepartmentId int
Department Department
}
type EmployeeContact struct{
gorm.Modal
EmpId int
EmpContactNo string
}
然后我们可以使用这个例子进行多个连接:
var department Department
db.
Model(&Department{}).
Where("DepName = ?", form.DepName).
Preload("Employees", func(tx *gorm.DB) *gorm.DB {
return tx.Preload("Department")
}).Find(&department)
您可以使用预加载
db.Preload("Department").
Preload("Employee.EmployeeContact").
Where(<condition>).
Find(&variable)
我认为文档非常简单:https://gorm.io/docs/preload.html#Preload.
我希望这有帮助