How to Perform Multiple Table Joins in GORM?

Multiple Table Joins with GORM

In GORM, performing multiple table joins is a convenient and straightforward process. Consider the following scenario:

You have three tables: Department, Employee, and EmployeeContact, with the following fields:

• Department: (gorm.Model, dep_name)
• Employee: (gorm.Model, emp_id, emp_name, department_id)
• EmployeeContact: (gorm.Model, employee_id, emp_contact_no)

To query these tables using GORM with a multi-table join, follow these steps:

<code class="go">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, ""
}</code>

By specifying the joined table names and their respective relationships, GORM automatically generates the necessary SQL query. In this example, the following SQL query is generated:

<code class="sql">SELECT * FROM department d, employee e, employeeContact ec WHERE d.id = e.department_id and e.id = ec.employee_id</code>

The Find method fills the results slice with instances of the relevant Go structs, making it easy to access the joined data.

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