Correct implementation of MySQL tables in MongoDB? - mysql

Question

I'm new to mongoDB, and I wonder how I can translate tables relations in MongoDB.
For example in my MySQL base, I have two tables : Manager and Employee.
Manager {
name: String,
ID: Int Primary Key
}
Employee {
name: String,
ID: Int Primary Key,
Manager: int Foreign key (Manager.ID)
}
I would like to know what is the correct way to implement this with MongoDB.

Answer 1

MongoDB is a non-relational document database.
'Document' is a record in a collection and each document can have any number of fields, including arrays, maps, etc. The strength and weakness of this are that two documents in the same collection may hold completely different fields. Normal forms of relational databases do not apply. Also, each document has a unique id.
How to link documents/collections together is completely up to the app logic.
Few options:
Keep everything together in once collection.
//
{
name: "Jon Appleseed",
manager: "Jonh Bosch"
},
{
name:"Another employee",
manager: "Jonh Bosch"
}
Use two collections as suggested by #iprakashv
Use a mixed approach:
// Employees
{
_id: "_234234",
name: "Jon Appleseed",
manager:{
name:"John Bosh",
id: _12321
}
},
{
_id: "_233234",
name: "Another employee",
manager:{
name:"John Bosh",
id: "_12321"
}
}
// Managers
{
_id: _123213,
name:"John Bosh",
subordinates:
[
{name:"Jon Appleseed", id: "_234234" },
{name:"Another employee", id: "_12321" },
]
}
As you see, you gain much more flexibility at the expense of normalization.

Answer 2

As mongodb is a NoSQL database for schema-less and relation-less collections (though you can put validations over a collection), join-less schema and nested objects make more sense here.
Now as per our requirement, each Manager object is linked to its employee so, should ideally have an array containing all its employee objects, but, it is not practical when we need all the employees irrespective of the Manager.
So, we may want to have just the array of employee id's instead of an array of employee objects and employee collection (table) to be maintained separately to fetch employee objects.
The samples documents for the above schema would look like:
//employee collection document
{
"ID": "E12334",
"name": "John Doe"
}
//manager collection document
{
"ID": "M453",
"name": "Jane Doe",
"employeeIDs": ["E12334", "E12343"]
}