In mongoDB Many-to-Many Relationship Data Modeling by Mark Starkman, he tries to see how many-to-many relationship can be implemented in the MongoDB database.
He suggests the following code will help us implement many-to-many relationship can be implemented in the MongoDB database:
An example of person's collections:
db.person.insert({
"_id": ObjectId("4e54ed9f48dc5922c0094a43"),
"firstName": "Joe",
"lastName": "Mongo",
"groups": [
ObjectId("4e54ed9f48dc5922c0094a42"),
ObjectId("4e54ed9f48dc5922c0094a41")
]
});
db.person.insert({
"_id": ObjectId("4e54ed9f48dc5922c0094a40"),
"firstName": "Sally",
"lastName": "Mongo",
"groups": [
ObjectId("4e54ed9f48dc5922c0094a42")
]
});
An example of Group collection:
db.groups.insert({
"_id": ObjectId("4e54ed9f48dc5922c0094a42"),
"groupName": "mongoDB User",
"persons": [
ObjectId("4e54ed9f48dc5922c0094a43"),
ObjectId("4e54ed9f48dc5922c0094a40")
]
});
db.groups.insert({
"_id": ObjectId("4e54ed9f48dc5922c0094a41"),
"groupName": "mongoDB Administrator",
"persons": [
ObjectId("4e54ed9f48dc5922c0094a43")
]
});
The aforementioned solution is alright if a person can belong to groups on the 100s, and vice versa for groups. However, Array of ObjectIds would Not be practical if a person can belong to 1000000 groups, and vice versa for groups.
What would be a better many-to-many solution in MongoDB of the relationship would number 1000000?
Best Answer
You can add a third collection, named
person_group, being described in that blog picture.