Definition
$objectToArrayConverts a document to an array. The return array contains an element for each field/value pair in the original document. Each element in the return array is a document that contains two fields
kandv:The
kfield contains the field name in the original document.The
vfield contains the value of the field in the original document.
$objectToArrayhas the following syntax:{ $objectToArray: <object> }The
<object>expression can be any valid expression as long as it resolves to a document object.$objectToArrayapplies to the top-level fields of its argument. If the argument is a document that itself contains embedded document fields, the$objectToArraydoes not recursively apply to the embedded document fields.For more information on expressions, see Expressions.
Behavior
For more information on expressions, see Expressions.
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Examples
$objectToArray Example
Consider a inventory collection with the following documents:
db.inventory.insertMany( [ { _id: 1, item: "ABC1", dimensions: { l: 25, w: 10, uom: "cm" } }, { _id: 2, item: "ABC2", dimensions: { l: 50, w: 25, uom: "cm" } }, { _id: 3, item: "XYZ1", dimensions: { l: 70, w: 75, uom: "cm" } }] )The following aggregation pipeline operation use the $objectToArray to return the dimensions field as an array:
db.inventory.aggregate( [ { $project: { item: 1, dimensions: { $objectToArray: "$dimensions" } } } ])The operation returns the following:
{ _id: 1, item: "ABC1", dimensions: [ { "k" : "l", "v" : 25 }, { "k" : "w", "v" : 10 }, { "k" : "uom", "v" : "cm" } ] }{ _id: 2, item: "ABC2", dimensions: [ { "k" : "l", "v" : 50 }, { "k" : "w", "v" : 25 }, { "k" : "uom", "v" : "cm" } ] }{ _id: 3, item: "XYZ1", dimensions: [ { "k" : "l", "v" : 70 }, { "k" : "w", "v" : 75 }, { "k" : "uom", "v" : "cm" } ] }$objectToArray to Sum Nested Fields
Consider a inventory collection with the following documents:
db.inventory.insertMany( [ { _id: 1, item: "ABC1", instock: { warehouse1: 2500, warehouse2: 500 } } { _id: 2, item: "ABC2", instock: { warehouse2: 500, warehouse3: 200} }] )The following aggregation pipeline operation uses the $objectToArray along with $unwind and $group to calculate the total items in stock per warehouse.
db.inventory.aggregate([ { $project: { warehouses: { $objectToArray: "$instock" } } }, { $unwind: "$warehouses" }, { $group: { _id: "$warehouses.k", total: { $sum: "$warehouses.v" } } }])The operation returns the following:
{ _id: "warehouse3", total: 200 }{ _id: "warehouse2", total: 1000 }{ _id: "warehouse1", total: 2500 }$objectToArray + $arrayToObject Example
Consider an inventory collection with the following documents:
db.inventory.insertMany( [ { _id: 1, item: "ABC1", instock: { warehouse1: 2500, warehouse2: 500 } }, { _id: 2, item: "ABC2", instock: { warehouse2: 500, warehouse3: 200}, }] )The following aggregation pipeline operation calculates the total in stock for each item and adds to the instock document:
db.inventory.aggregate( [ { $addFields: { instock: { $objectToArray: "$instock" } } }, { $addFields: { instock: { $concatArrays: [ "$instock", [ { "k": "total", "v": { $sum: "$instock.v" } } ] ] } } } , { $addFields: { instock: { $arrayToObject: "$instock" } } }] )The operation returns the following:
{ _id: 1, item: "ABC1", instock: { warehouse1: 2500, warehouse2: 500, total: 3000 } }{ _id: 2, item: "ABC2", instock: { warehouse2: 500, warehouse3: 200, total: 700 } }