0Graph lookup helps find connected data that links to itself, like family trees or company hierarchies.
db.collection.aggregate([
{
$graphLookup: {
from: "collectionName",
startWith: "$fieldToStart",
connectFromField: "fieldToFollow",
connectToField: "fieldToMatch",
as: "outputArray",
maxDepth: <number>, // optional
depthField: "depthFieldName" // optional
}
}
])from is the collection to search recursively.
startWith is the value to start the search from.
db.employees.aggregate([
{
$graphLookup: {
from: "employees",
startWith: "$managerId",
connectFromField: "employeeId",
connectToField: "managerId",
as: "subordinates"
}
}
])db.categories.aggregate([
{
$graphLookup: {
from: "categories",
startWith: "$_id",
connectFromField: "_id",
connectToField: "parentId",
as: "allSubcategories",
maxDepth: 3,
depthField: "level"
}
}
])db.products.aggregate([
{
$graphLookup: {
from: "products",
startWith: "$componentId",
connectFromField: "_id",
connectToField: "componentId",
as: "allComponents"
}
}
])This inserts employees with managers and finds all subordinates for each employee recursively.
db.employees.insertMany([
{ employeeId: 1, name: "Alice", managerId: null },
{ employeeId: 2, name: "Bob", managerId: 1 },
{ employeeId: 3, name: "Charlie", managerId: 1 },
{ employeeId: 4, name: "David", managerId: 2 },
{ employeeId: 5, name: "Eve", managerId: 2 }
])
// Find all subordinates under each employee
const result = db.employees.aggregate([
{
$graphLookup: {
from: "employees",
startWith: "$managerId",
connectFromField: "employeeId",
connectToField: "managerId",
as: "subordinates"
}
}
]).toArray()
printjson(result)Time complexity depends on the size and depth of the graph.
Space complexity grows with the number of connected documents found.
Common mistake: mixing up connectFromField and connectToField causes no results.
Use $graphLookup when you need recursive search; use $lookup for simple joins.
$graphLookup helps find connected data recursively in the same collection.
It is useful for hierarchical or network data like employees or categories.
Remember to set correct fields for starting point and connections.
$graphLookup stage in MongoDB aggregation?$graphLookup stage in a MongoDB aggregation pipeline?startWith uses the field to start recursion, usually a reference like "$managerId". The connectToField is the field in the foreign documents to match against the start value, here "_id". The connectFromField is the field in the foreign document used for the next recursion, here "managerId".startWith: "$managerId", connectFromField: "managerId", and connectToField: "_id". Others swap these or use incorrect field names.categories with documents:{"_id": 1, "name": "Electronics", "parent": null}{"_id": 2, "name": "Computers", "parent": 1}{"_id": 3, "name": "Laptops", "parent": 2}[ { "$graphLookup": { "from": "categories", "startWith": "$parent", "connectFromField": "parent", "connectToField": "_id", "as": "ancestors" } } ]_id: 3?startWith uses its parent field which is 2. Then it finds documents where _id matches 2, then recursively finds parents of 2, which is 1.{ "$graphLookup": { "from": "employees", "startWith": "$managerId", "connectFromField": "managerId", "connectToField": "_id", "as": "team" } }managerId field?managerId field, startWith evaluates to null or undefined, so the recursion has no starting point.startWith is null or missing, recursion cannot start -> Option Cemployees where each document has _id and managerId. You want to find all employees under a manager recursively, including the manager. Which $graphLookup configuration correctly achieves this?_id. Then find employees whose managerId matches this _id, recursively.startWith should be $_id (the manager's id). connectToField is managerId (field in employees to match), and connectFromField is _id (field to match against for next level).$managerId are wrong for this use case.Pass the test and this pattern moves unknown strong while earning +1 Grip toward your certificate.